HAProxy version 1.5.18 – Configuration Manual

May 4, 2021

Configuration Manual

version 1.5.18


willy tarreau
2016/05/10

This document covers the configuration language as implemented in the version specified above. It does not provide any hint, example or advice. For such documentation, please refer to the Reference Manual or the Architecture Manual. The summary below is meant to help you search sections by name and navigate through the document. Note to documentation contributors : This document is formatted with 80 columns per line, with even number of spaces for indentation and without tabs. Please follow these rules strictly so that it remains easily printable everywhere. If a line needs to be printed verbatim and does not fit, please end each line with a backslash (”) and continue on next line, indented by two characters. It is also sometimes useful to prefix all output lines (logs, console outs) with 3 closing angle brackets (‘>>>’) in order to help get the difference between inputs and outputs when it can become ambiguous. If you add sections, please update the summary below for easier searching. When haproxy is running in HTTP mode, both the request and the response are fully analyzed and indexed, thus it becomes possible to build matching criteria on almost anything found in the contents. However, it is important to understand how HTTP requests and responses are formed, and how HAProxy decomposes them. It will then become easier to write correct rules and to debug existing configurations.

1.1. The HTTP transaction model

The HTTP protocol is transaction-driven. This means that each request will lead to one and only one response. Traditionally, a TCP connection is established from the client to the server, a request is sent by the client on the connection, the server responds and the connection is closed. A new request will involve a new connection : [CON1] [REQ1] … [RESP1] [CLO1] [CON2] [REQ2] … [RESP2] [CLO2] … In this mode, called the “HTTP close” mode, there are as many connection establishments as there are HTTP transactions. Since the connection is closed by the server after the response, the client does not need to know the content length. Due to the transactional nature of the protocol, it was possible to improve it to avoid closing a connection between two subsequent transactions. In this mode however, it is mandatory that the server indicates the content length for each response so that the client does not wait indefinitely. For this, a special header is used: “Content-length”. This mode is called the “keep-alive” mode : [CON] [REQ1] … [RESP1] [REQ2] … [RESP2] [CLO] … Its advantages are a reduced latency between transactions, and less processing power required on the server side. It is generally better than the close mode, but not always because the clients often limit their concurrent connections to a smaller value. A last improvement in the communications is the pipelining mode. It still uses keep-alive, but the client does not wait for the first response to send the second request. This is useful for fetching large number of images composing a page : [CON] [REQ1] [REQ2] … [RESP1] [RESP2] [CLO] … This can obviously have a tremendous benefit on performance because the network latency is eliminated between subsequent requests. Many HTTP agents do not correctly support pipelining since there is no way to associate a response with the corresponding request in HTTP. For this reason, it is mandatory for the server to reply in the exact same order as the requests were received. By default HAProxy operates in keep-alive mode with regards to persistent connections: for each connection it processes each request and response, and leaves the connection idle on both sides between the end of a response and the start of a new request. HAProxy supports 5 connection modes : – keep alive : all requests and responses are processed (default) – tunnel : only the first request and response are processed, everything else is forwarded with no analysis. – passive close : tunnel with “Connection: close” added in both directions. – server close : the server-facing connection is closed after the response. – forced close : the connection is actively closed after end of response.

1.2. HTTP request

First, let’s consider this HTTP request : Line Contents number 1 GET /serv/login.php?lang=en&profile=2 HTTP/1.1 2 Host: www.mydomain.com 3 User-agent: my small browser 4 Accept: image/jpeg, image/gif 5 Accept: image/png

1.2.1. The Request line

Line 1 is the “request line”. It is always composed of 3 fields : – a METHOD : GET – a URI : /serv/login.php?lang=en&profile=2 – a version tag : HTTP/1.1 All of them are delimited by what the standard calls LWS (linear white spaces), which are commonly spaces, but can also be tabs or line feeds/carriage returns followed by spaces/tabs. The method itself cannot contain any colon (‘:’) and is limited to alphabetic letters. All those various combinations make it desirable that HAProxy performs the splitting itself rather than leaving it to the user to write a complex or inaccurate regular expression. The URI itself can have several forms : – A “relative URI” : /serv/login.php?lang=en&profile=2 It is a complete URL without the host part. This is generally what is received by servers, reverse proxies and transparent proxies. – An “absolute URI”, also called a “URL” : http://192.168.0.12:8080/serv/login.php?lang=en&profile=2 It is composed of a “scheme” (the protocol name followed by ‘://’), a host name or address, optionally a colon (‘:’) followed by a port number, then a relative URI beginning at the first slash (‘/’) after the address part. This is generally what proxies receive, but a server supporting HTTP/1.1 must accept this form too. – a star (‘*’) : this form is only accepted in association with the OPTIONS method and is not relayable. It is used to inquiry a next hop’s capabilities. – an address:port combination : 192.168.0.12:80 This is used with the CONNECT method, which is used to establish TCP tunnels through HTTP proxies, generally for HTTPS, but sometimes for other protocols too. In a relative URI, two sub-parts are identified. The part before the question mark is called the “path“. It is typically the relative path to static objects on the server. The part after the question mark is called the “query string”. It is mostly used with GET requests sent to dynamic scripts and is very specific to the language, framework or application in use.

1.2.2. The request headers

The headers start at the second line. They are composed of a name at the beginning of the line, immediately followed by a colon (‘:’). Traditionally, an LWS is added after the colon but that’s not required. Then come the values. Multiple identical headers may be folded into one single line, delimiting the values with commas, provided that their order is respected. This is commonly encountered in the “Cookie:” field. A header may span over multiple lines if the subsequent lines begin with an LWS. In the example in 1.2, lines 4 and 5 define a total of 3 values for the “Accept:” header. Contrary to a common mis-conception, header names are not case-sensitive, and their values are not either if they refer to other header names (such as the “Connection:” header). The end of the headers is indicated by the first empty line. People often say that it’s a double line feed, which is not exact, even if a double line feed is one valid form of empty line. Fortunately, HAProxy takes care of all these complex combinations when indexing headers, checking values and counting them, so there is no reason to worry about the way they could be written, but it is important not to accuse an application of being buggy if it does unusual, valid things. Important note: As suggested by RFC2616, HAProxy normalizes headers by replacing line breaks in the middle of headers by LWS in order to join multi-line headers. This is necessary for proper analysis and helps less capable HTTP parsers to work correctly and not to be fooled by such complex constructs.

1.3. HTTP response

An HTTP response looks very much like an HTTP request. Both are called HTTP messages. Let’s consider this HTTP response : Line Contents number 1 HTTP/1.1 200 OK 2 Content-length: 350 3 Content-Type: text/html As a special case, HTTP supports so called “Informational responses” as status codes 1xx. These messages are special in that they don’t convey any part of the response, they’re just used as sort of a signaling message to ask a client to continue to post its request for instance. In the case of a status 100 response the requested information will be carried by the next non-100 response message following the informational one. This implies that multiple responses may be sent to a single request, and that this only works when keep-alive is enabled (1xx messages are HTTP/1.1 only). HAProxy handles these messages and is able to correctly forward and skip them, and only process the next non-100 response. As such, these messages are neither logged nor transformed, unless explicitly state otherwise. Status 101 messages indicate that the protocol is changing over the same connection and that haproxy must switch to tunnel mode, just as if a CONNECT had occurred. Then the Upgrade header would contain additional information about the type of protocol the connection is switching to.

1.3.1. The Response line

Line 1 is the “response line”. It is always composed of 3 fields : – a version tag : HTTP/1.1 – a status code : 200 – a reason : OK The status code is always 3-digit. The first digit indicates a general status : – 1xx = informational message to be skipped (eg: 100, 101) – 2xx = OK, content is following (eg: 200, 206) – 3xx = OK, no content following (eg: 302, 304) – 4xx = error caused by the client (eg: 401, 403, 404) – 5xx = error caused by the server (eg: 500, 502, 503) Please refer to RFC2616 for the detailed meaning of all such codes. The “reason” field is just a hint, but is not parsed by clients. Anything can be found there, but it’s a common practice to respect the well-established messages. It can be composed of one or multiple words, such as “OK”, “Found”, or “Authentication Required”. Haproxy may emit the following status codes by itself : Code When / reason 200 access to stats page, and when replying to monitoring requests 301 when performing a redirection, depending on the configured code 302 when performing a redirection, depending on the configured code 303 when performing a redirection, depending on the configured code 307 when performing a redirection, depending on the configured code 308 when performing a redirection, depending on the configured code 400 for an invalid or too large request 401 when an authentication is required to perform the action (when accessing the stats page) 403 when a request is forbidden by a “block” ACL or “reqdeny” filter 408 when the request timeout strikes before the request is complete 500 when haproxy encounters an unrecoverable internal error, such as a memory allocation failure, which should never happen 502 when the server returns an empty, invalid or incomplete response, or when an “rspdeny” filter blocks the response. 503 when no server was available to handle the request, or in response to monitoring requests which match the “monitor fail” condition 504 when the response timeout strikes before the server responds The error 4xx and 5xx codes above may be customized (see “errorloc” in section 4.2).

1.3.2. The response headers

Response headers work exactly like request headers, and as such, HAProxy uses the same parsing function for both. Please refer to paragraph 1.2.2 for more details.

2.1. Configuration file format

HAProxy’s configuration process involves 3 major sources of parameters : – the arguments from the command-line, which always take precedence – the “global” section, which sets process-wide parameters – the proxies sections which can take form of “defaults”, “listen”, “frontend” and “backend”. The configuration file syntax consists in lines beginning with a keyword referenced in this manual, optionally followed by one or several parameters delimited by spaces. If spaces have to be entered in strings, then they must be preceded by a backslash (”) to be escaped. Backslashes also have to be escaped by doubling them.

2.2. Time format

Some parameters involve values representing time, such as timeouts. These values are generally expressed in milliseconds (unless explicitly stated otherwise) but may be expressed in any other unit by suffixing the unit to the numeric value. It is important to consider this because it will not be repeated for every keyword. Supported units are : – us : microseconds. 1 microsecond = 1/1000000 second – ms : milliseconds. 1 millisecond = 1/1000 second. This is the default. – s : seconds. 1s = 1000ms – m : minutes. 1m = 60s = 60000ms – h : hours. 1h = 60m = 3600s = 3600000ms – d : days. 1d = 24h = 1440m = 86400s = 86400000ms

2.3. Examples

# Simple configuration for an HTTP proxy listening on port 80 on all # interfaces and forwarding requests to a single backend “servers” with a # single server “server1” listening on 127.0.0.1:8000 global daemon maxconn 256 defaults mode http timeout connect 5000ms timeout client 50000ms timeout server 50000ms frontend http-in bind *:80 default_backend servers backend servers server server1 127.0.0.1:8000 maxconn 32 # The same configuration defined with a single listen block. Shorter but # less expressive, especially in HTTP mode. global daemon maxconn 256 defaults mode http timeout connect 5000ms timeout client 50000ms timeout server 50000ms listen http-in bind *:80 server server1 127.0.0.1:8000 maxconn 32 Assuming haproxy is in $PATH, test these configurations in a shell with: $ sudo haproxy -f configuration.conf -c

3.1. Process management and security

Assigns a default directory to fetch SSL CA certificates and CRLs from when a relative path is used with “ca-file” or “crl-file” directives. Absolute locations specified in “ca-file” and “crl-file” prevail and ignore “ca-base“. Changes current directory to and performs a chroot() there before dropping privileges. This increases the security level in case an unknown vulnerability would be exploited, since it would make it very hard for the attacker to exploit the system. This only works when the process is started with superuser privileges. It is important to ensure that is both empty and unwritable to anyone. cpu-map <"all"|"odd"|"even"|process_num> …On Linux 2.6 and above, it is possible to bind a process to a specific CPU set. This means that the process will never run on other CPUs. The “cpu-map” directive specifies CPU sets for process sets. The first argument is the process number to bind. This process must have a number between 1 and 32 or 64, depending on the machine’s word size, and any process IDs above nbproc are ignored. It is possible to specify all processes at once using “all”, only odd numbers using “odd” or even numbers using “even”, just like with the “bind-process” directive. The second and forthcoming arguments are CPU sets. Each CPU set is either a unique number between 0 and 31 or 63 or a range with two such numbers delimited by a dash (‘-‘). Multiple CPU numbers or ranges may be specified, and the processes will be allowed to bind to all of them. Obviously, multiple “cpu-map” directives may be specified. Each “cpu-map” directive will replace the previous ones when they overlap. Assigns a default directory to fetch SSL certificates from when a relative path is used with “crtfile” directives. Absolute locations specified after “crtfile” prevail and ignore “crt-base“. Makes the process fork into background. This is the recommended mode of operation. It is equivalent to the command line “-D” argument. It can be disabled by the command line “-db” argument. Changes the process’ group ID to . It is recommended that the group ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must be started with a user belonging to this group, or with superuser privileges. Note that if haproxy is started from a user having supplementary groups, it will only be able to drop these groups if started with superuser privileges. See also “group” and “uid“. Similar to “gid” but uses the GID of group name from /etc/group. See also “gid” and “user“. log

[len ] [max level [min level]]Adds a global syslog server. Up to two global servers can be defined. They will receive logs for startups and exits, as well as all logs from proxies configured with “log global“.

can be one of: – An IPv4 address optionally followed by a colon and a UDP port. If no port is specified, 514 is used by default (the standard syslog port). – An IPv6 address followed by a colon and optionally a UDP port. If no port is specified, 514 is used by default (the standard syslog port). – A filesystem path to a UNIX domain socket, keeping in mind considerations for chroot (be sure the path is accessible inside the chroot) and uid/gid (be sure the path is appropriately writeable). Any part of the address string may reference any number of environment variables by preceding their name with a dollar sign (‘$’) and optionally enclosing them with braces (‘{}’), similarly to what is done in Bourne shell. is an optional maximum line length. Log lines larger than this value will be truncated before being sent. The reason is that syslog servers act differently on log line length. All servers support the default value of 1024, but some servers simply drop larger lines while others do log them. If a server supports long lines, it may make sense to set this value here in order to avoid truncating long lines. Similarly, if a server drops long lines, it is preferable to truncate them before sending them. Accepted values are 80 to 65535 inclusive. The default value of 1024 is generally fine for all standard usages. Some specific cases of long captures or JSON-formated logs may require larger values. must be one of the 24 standard syslog facilities : kern user mail daemon auth syslog lpr news uucp cron auth2 ftp ntp audit alert cron2 local0 local1 local2 local3 local4 local5 local6 local7 An optional level can be specified to filter outgoing messages. By default, all messages are sent. If a maximum level is specified, only messages with a severity at least as important as this level will be sent. An optional minimum level can be specified. If it is set, logs emitted with a more severe level than this one will be capped to this level. This is used to avoid sending “emerg” messages on all terminals on some default syslog configurations. Eight levels are known : emerg alert crit err warning notice info debug Sets the hostname field in the syslog header. If optional “string” parameter is set the header is set to the string contents, otherwise uses the hostname of the system. Generally used if one is not relaying logs through an intermediate syslog server or for simply customizing the hostname printed in the logs. Sets the tag field in the syslog header to this string. It defaults to the program name as launched from the command line, which usually is “haproxy”. Sometimes it can be useful to differentiate between multiple processes running on the same host. Creates processes when going daemon. This requires the “daemon” mode. By default, only one process is created, which is the recommended mode of operation. For systems limited to small sets of file descriptors per process, it may be needed to fork multiple daemons. USING MULTIPLE PROCESSES IS HARDER TO DEBUG AND IS REALLY DISCOURAGED. See also “daemon“. Writes pids of all daemons into file . This option is equivalent to the “-p” command line argument. The file must be accessible to the user starting the process. See also “daemon“. Limits the stats socket to a certain set of processes numbers. By default the stats socket is bound to all processes, causing a warning to be emitted when nbproc is greater than 1 because there is no way to select the target process when connecting. However, by using this setting, it becomes possible to pin the stats socket to a specific set of processes, typically the first one. The warning will automatically be disabled when this setting is used, whatever the number of processes used. The maximum process ID depends on the machine’s word size (32 or 64). A better option consists in using the “process” setting of the “stats socket” line to force the process on each line. This setting is only available when support for OpenSSL was built in. It sets the default string describing the list of cipher algorithms (“cipher suite”) that are negotiated during the SSL/TLS handshake for all “bind” lines which do not explicitly define theirs. The format of the string is defined in “man 1 ciphers” from OpenSSL man pages, and can be for instance a string such as “AES:ALL:!aNULL:!eNULL:+RC4:@STRENGTH” (without quotes). Please check the “bind” keyword for more information. This setting is only available when support for OpenSSL was built in. It sets default ssl-options to force on all “bind” lines. Please check the “bind” keyword to see available options. Example: global ssl-default-bind-options no-sslv3 no-tls-tickets This setting is only available when support for OpenSSL was built in. It sets the default string describing the list of cipher algorithms that are negotiated during the SSL/TLS handshake with the server, for all “server” lines which do not explicitly define theirs. The format of the string is defined in “man 1 ciphers”. Please check the “server” keyword for more information. This setting is only available when support for OpenSSL was built in. It sets default ssl-options to force on all “server” lines. Please check the “server” keyword to see available options. The default behavior for SSL verify on servers side. If specified to ‘none’, servers certificates are not verified. The default is ‘required’ except if forced using cmdline option ‘-dV’. Binds a UNIX socket to or a TCPv4/v6 address to . Connections to this socket will return various statistics outputs and even allow some commands to be issued to change some runtime settings. Please consult section 9.2 “Unix Socket commands” for more details. All parameters supported by “bind” lines are supported, for instance to restrict access to some users or their access rights. Please consult section 5.1 for more information. The default timeout on the stats socket is set to 10 seconds. It is possible to change this value with “stats timeout“. The value must be passed in milliseconds, or be suffixed by a time unit among { us, ms, s, m, h, d }. By default, the stats socket is limited to 10 concurrent connections. It is possible to change this value with “stats maxconn“. Changes the process’ user ID to . It is recommended that the user ID is dedicated to HAProxy or to a small set of similar daemons. HAProxy must be started with superuser privileges in order to be able to switch to another one. See also “gid” and “user“. Sets the maximum number of per-process file-descriptors to . By default, it is automatically computed, so it is recommended not to use this option. unix-bind [ prefix ] [ mode ] [ user ] [ uid ] [ group ] [ gid ]Fixes common settings to UNIX listening sockets declared in “bind” statements. This is mainly used to simplify declaration of those UNIX sockets and reduce the risk of errors, since those settings are most commonly required but are also process-specific. The setting can be used to force all socket path to be relative to that directory. This might be needed to access another component’s chroot. Note that those paths are resolved before haproxy chroots itself, so they are absolute. The , , , and all have the same meaning as their homonyms used by the “bind” statement. If both are specified, the “bind” statement has priority, meaning that the “unix-bind” settings may be seen as process-wide default settings. Similar to “uid” but uses the UID of user name from /etc/passwd. See also “uid” and “group“. Only letters, digits, hyphen and underscore are allowed, like in DNS names. This statement is useful in HA configurations where two or more processes or servers share the same IP address. By setting a different node-name on all nodes, it becomes easy to immediately spot what server is handling the traffic. Add a text that describes the instance. Please note that it is required to escape certain characters (# for example) and this text is inserted into a html page so you should avoid using “<" and ">” characters.

3.2. Performance tuning

By default, haproxy tries to spread the start of health checks across the smallest health check interval of all the servers in a farm. The principle is to avoid hammering services running on the same server. But when using large check intervals (10 seconds or more), the last servers in the farm take some time before starting to be tested, which can be a problem. This parameter is used to enforce an upper bound on delay between the first and the last check, even if the servers’ check intervals are larger. When servers run with shorter intervals, their intervals will be respected though. Sets the maximum per-process number of concurrent connections to . It is equivalent to the command-line argument “-n”. Proxies will stop accepting connections when this limit is reached. The “ulimit-n” parameter is automatically adjusted according to this value. See also “ulimit-n“. Note: the “select” poller cannot reliably use more than 1024 file descriptors on some platforms. If your platform only supports select and reports “select FAILED” on startup, you need to reduce maxconn until it works (slightly below 500 in general). Sets the maximum per-process number of connections per second to . Proxies will stop accepting connections when this limit is reached. It can be used to limit the global capacity regardless of each frontend capacity. It is important to note that this can only be used as a service protection measure, as there will not necessarily be a fair share between frontends when the limit is reached, so it’s a good idea to also limit each frontend to some value close to its expected share. Also, lowering tune.maxaccept can improve fairness. Sets the maximum per-process input compression rate to kilobytes per second. For each session, if the maximum is reached, the compression level will be decreased during the session. If the maximum is reached at the beginning of a session, the session will not compress at all. If the maximum is not reached, the compression level will be increased up to tune.comp.maxlevel. A value of zero means there is no limit, this is the default value. Sets the maximum CPU usage HAProxy can reach before stopping the compression for new requests or decreasing the compression level of current requests. It works like ‘maxcomprate’ but measures CPU usage instead of incoming data bandwidth. The value is expressed in percent of the CPU used by haproxy. In case of multiple processes (nbproc > 1), each process manages its individual usage. A value of 100 disable the limit. The default value is 100. Setting a lower value will prevent the compression work from slowing the whole process down and from introducing high latencies. Sets the maximum per-process number of pipes to . Currently, pipes are only used by kernel-based tcp splicing. Since a pipe contains two file descriptors, the “ulimit-n” value will be increased accordingly. The default value is maxconn/4, which seems to be more than enough for most heavy usages. The splice code dynamically allocates and releases pipes, and can fall back to standard copy, so setting this value too low may only impact performance. Sets the maximum per-process number of sessions per second to . Proxies will stop accepting connections when this limit is reached. It can be used to limit the global capacity regardless of each frontend capacity. It is important to note that this can only be used as a service protection measure, as there will not necessarily be a fair share between frontends when the limit is reached, so it’s a good idea to also limit each frontend to some value close to its expected share. Also, lowering tune.maxaccept can improve fairness. Sets the maximum per-process number of concurrent SSL connections to . By default there is no SSL-specific limit, which means that the global maxconn setting will apply to all connections. Setting this limit avoids having openssl use too much memory and crash when malloc returns NULL (since it unfortunately does not reliably check for such conditions). Note that the limit applies both to incoming and outgoing connections, so one connection which is deciphered then ciphered accounts for 2 SSL connections. Sets the maximum per-process number of SSL sessions per second to . SSL listeners will stop accepting connections when this limit is reached. It can be used to limit the global SSL CPU usage regardless of each frontend capacity. It is important to note that this can only be used as a service protection measure, as there will not necessarily be a fair share between frontends when the limit is reached, so it’s a good idea to also limit each frontend to some value close to its expected share. It is also important to note that the sessions are accounted before they enter the SSL stack and not after, which also protects the stack against bad handshakes. Also, lowering tune.maxaccept can improve fairness. Sets the maximum amount of RAM in megabytes per process usable by the zlib. When the maximum amount is reached, future sessions will not compress as long as RAM is unavailable. When sets to 0, there is no limit. The default value is 0. The value is available in bytes on the UNIX socket with “show info” on the line “MaxZlibMemUsage”, the memory used by zlib is “ZlibMemUsage” in bytes. Disables the use of the “epoll” event polling system on Linux. It is equivalent to the command-line argument “-de”. The next polling system used will generally be “poll”. See also “nopoll“. Disables the use of the “kqueue” event polling system on BSD. It is equivalent to the command-line argument “-dk”. The next polling system used will generally be “poll”. See also “nopoll“. Disables the use of the “poll” event polling system. It is equivalent to the command-line argument “-dp”. The next polling system used will be “select”. It should never be needed to disable “poll” since it’s available on all platforms supported by HAProxy. See also “nokqueue” and “noepoll“. Disables the use of kernel tcp splicing between sockets on Linux. It is equivalent to the command line argument “-dS”. Data will then be copied using conventional and more portable recv/send calls. Kernel tcp splicing is limited to some very recent instances of kernel 2.6. Most versions between 2.6.25 and 2.6.28 are buggy and will forward corrupted data, so they must not be used. This option makes it easier to globally disable kernel splicing in case of doubt. See also “option splice-auto“, “option splice-request” and “option splice-response“. Disables the use of getaddrinfo(3) for name resolving. It is equivalent to the command line argument “-dG”. Deprecated gethostbyname(3) will be used. Sometimes it is desirable to avoid sending agent and health checks to servers at exact intervals, for instance when many logical servers are located on the same physical server. With the help of this parameter, it becomes possible to add some randomness in the check interval between 0 and +/- 50%. A value between 2 and 5 seems to show good results. The default value remains at 0. Sets the buffer size to this size (in bytes). Lower values allow more sessions to coexist in the same amount of RAM, and higher values allow some applications with very large cookies to work. The default value is 16384 and can be changed at build time. It is strongly recommended not to change this from the default value, as very low values will break some services such as statistics, and values larger than default size will increase memory usage, possibly causing the system to run out of memory. At least the global maxconn parameter should be decreased by the same factor as this one is increased. If HTTP request is larger than (tune.bufsize – tune.maxrewrite), haproxy will return HTTP 400 (Bad Request) error. Similarly if an HTTP response is larger than this size, haproxy will return HTTP 502 (Bad Gateway). Sets the check buffer size to this size (in bytes). Higher values may help find string or regex patterns in very large pages, though doing so may imply more memory and CPU usage. The default value is 16384 and can be changed at build time. It is not recommended to change this value, but to use better checks whenever possible. Sets the maximum compression level. The compression level affects CPU usage during compression. This value affects CPU usage during compression. Each session using compression initializes the compression algorithm with this value. The default value is 1. Sets the maximum length of captured cookies. This is the maximum value that the “capture cookie xxx len yyy” will be allowed to take, and any upper value will automatically be truncated to this one. It is important not to set too high a value because all cookie captures still allocate this size whatever their configured value (they share a same pool). This value is per request per response, so the memory allocated is twice this value per connection. When not specified, the limit is set to 63 characters. It is recommended not to change this value. Sets the maximum number of headers in a request. When a request comes with a number of headers greater than this value (including the first line), it is rejected with a “400 Bad Request” status code. Similarly, too large responses are blocked with “502 Bad Gateway”. The default value is 101, which is enough for all usages, considering that the widely deployed Apache server uses the same limit. It can be useful to push this limit further to temporarily allow a buggy application to work by the time it gets fixed. Keep in mind that each new header consumes 32bits of memory for each session, so don’t push this limit too high. Sets the duration after which haproxy will consider that an empty buffer is probably associated with an idle stream. This is used to optimally adjust some packet sizes while forwarding large and small data alternatively. The decision to use splice() or to send large buffers in SSL is modulated by this parameter. The value is in milliseconds between 0 and 65535. A value of zero means that haproxy will not try to detect idle streams. The default is 1000, which seems to correctly detect end user pauses (eg: read a page before clicking). There should be not reason for changing this value. Please check tune.ssl.maxrecord below. Sets the maximum number of consecutive connections a process may accept in a row before switching to other work. In single process mode, higher numbers give better performance at high connection rates. However in multi-process modes, keeping a bit of fairness between processes generally is better to increase performance. This value applies individually to each listener, so that the number of processes a listener is bound to is taken into account. This value defaults to 64. In multi-process mode, it is divided by twice the number of processes the listener is bound to. Setting this value to -1 completely disables the limitation. It should normally not be needed to tweak this value. Sets the maximum amount of events that can be processed at once in a call to the polling system. The default value is adapted to the operating system. It has been noticed that reducing it below 200 tends to slightly decrease latency at the expense of network bandwidth, and increasing it above 200 tends to trade latency for slightly increased bandwidth. Sets the reserved buffer space to this size in bytes. The reserved space is used for header rewriting or appending. The first reads on sockets will never fill more than bufsize-maxrewrite. Historically it has defaulted to half of bufsize, though that does not make much sense since there are rarely large numbers of headers to add. Setting it too high prevents processing of large requests or responses. Setting it too low prevents addition of new headers to already large requests or to POST requests. It is generally wise to set it to about 1024. It is automatically readjusted to half of bufsize if it is larger than that. This means you don’t have to worry about it when changing bufsize. Sets the kernel pipe buffer size to this size (in bytes). By default, pipes are the default size for the system. But sometimes when using TCP splicing, it can improve performance to increase pipe sizes, especially if it is suspected that pipes are not filled and that many calls to splice() are performed. This has an impact on the kernel’s memory footprint, so this must not be changed if impacts are not understood. Forces the kernel socket receive buffer size on the client or the server side to the specified value in bytes. This value applies to all TCP/HTTP frontends and backends. It should normally never be set, and the default size (0) lets the kernel autotune this value depending on the amount of available memory. However it can sometimes help to set it to very low values (eg: 4096) in order to save kernel memory by preventing it from buffering too large amounts of received data. Lower values will significantly increase CPU usage though. Forces the kernel socket send buffer size on the client or the server side to the specified value in bytes. This value applies to all TCP/HTTP frontends and backends. It should normally never be set, and the default size (0) lets the kernel autotune this value depending on the amount of available memory. However it can sometimes help to set it to very low values (eg: 4096) in order to save kernel memory by preventing it from buffering too large amounts of received data. Lower values will significantly increase CPU usage though. Another use case is to prevent write timeouts with extremely slow clients due to the kernel waiting for a large part of the buffer to be read before notifying haproxy again. Sets the size of the global SSL session cache, in a number of blocks. A block is large enough to contain an encoded session without peer certificate. An encoded session with peer certificate is stored in multiple blocks depending on the size of the peer certificate. A block uses approximately 200 bytes of memory. The default value may be forced at build time, otherwise defaults to 20000. When the cache is full, the most idle entries are purged and reassigned. Higher values reduce the occurrence of such a purge, hence the number of CPU-intensive SSL handshakes by ensuring that all users keep their session as long as possible. All entries are pre-allocated upon startup and are shared between all processes if “nbproc” is greater than 1. Setting this value to 0 disables the SSL session cache. This boolean disables SSL session cache sharing between all processes. It should normally not be used since it will force many renegotiations due to clients hitting a random process. But it may be required on some operating systems where none of the SSL cache synchronization method may be used. In this case, adding a first layer of hash-based load balancing before the SSL layer might limit the impact of the lack of session sharing. Sets how long a cached SSL session may remain valid. This time is expressed in seconds and defaults to 300 (5 min). It is important to understand that it does not guarantee that sessions will last that long, because if the cache is full, the longest idle sessions will be purged despite their configured lifetime. The real usefulness of this setting is to prevent sessions from being used for too long. Sets the maximum amount of bytes passed to SSL_write() at a time. Default value 0 means there is no limit. Over SSL/TLS, the client can decipher the data only once it has received a full record. With large records, it means that clients might have to download up to 16kB of data before starting to process them. Limiting the value can improve page load times on browsers located over high latency or low bandwidth networks. It is suggested to find optimal values which fit into 1 or 2 TCP segments (generally 1448 bytes over Ethernet with TCP timestamps enabled, or 1460 when timestamps are disabled), keeping in mind that SSL/TLS add some overhead. Typical values of 1419 and 2859 gave good results during tests. Use “strace -e trace=write” to find the best value. Haproxy will automatically switch to this setting after an idle stream has been detected (see tune.idletimer above). Sets the maximum size of the Diffie-Hellman parameters used for generating the ephemeral/temporary Diffie-Hellman key in case of DHE key exchange. The final size will try to match the size of the server’s RSA (or DSA) key (e.g, a 2048 bits temporary DH key for a 2048 bits RSA key), but will not exceed this maximum value. Default value if 1024. Only 1024 or higher values are allowed. Higher values will increase the CPU load, and values greater than 1024 bits are not supported by Java 7 and earlier clients. This value is not used if static Diffie-Hellman parameters are supplied via the certificate file. Sets the memLevel parameter in zlib initialization for each session. It defines how much memory should be allocated for the internal compression state. A value of 1 uses minimum memory but is slow and reduces compression ratio, a value of 9 uses maximum memory for optimal speed. Can be a value between 1 and 9. The default value is 8. Sets the window size (the size of the history buffer) as a parameter of the zlib initialization for each session. Larger values of this parameter result in better compression at the expense of memory usage. Can be a value between 8 and 15. The default value is 15.

3.3. Debugging

Enables debug mode which dumps to stdout all exchanges, and disables forking into background. It is the equivalent of the command-line argument “-d”. It should never be used in a production configuration since it may prevent full system startup. Do not display any message during startup. It is equivalent to the command- line argument “-q”.

3.4. Userlists

It is possible to control access to frontend/backend/listen sections or to http stats by allowing only authenticated and authorized users. To do this, it is required to create at least one userlist and to define users. Creates new userlist with name . Many independent userlists can be used to store authentication & authorization data for independent customers. group [users ,,(…)]Adds group to the current userlist. It is also possible to attach users to this group by using a comma separated list of names proceeded by “users” keyword. user [password|insecure-password ] [groups ,,(…)]Adds user to the current userlist. Both secure (encrypted) and insecure (unencrypted) passwords can be used. Encrypted passwords are evaluated using the crypt(3) function so depending of the system’s capabilities, different algorithms are supported. For example modern Glibc based Linux system supports MD5, SHA-256, SHA-512 and of course classic, DES-based method of encrypting passwords. Example: userlist L1 group G1 users tiger,scott group G2 users xdb,scott user tiger password $6$k6y3o.eP$JlKBx9za9667qe4(…)xHSwRv6J.C0/D7cV91 user scott insecure-password elgato user xdb insecure-password hello userlist L2 group G1 group G2 user tiger password $6$k6y3o.eP$JlKBx(…)xHSwRv6J.C0/D7cV91 groups G1 user scott insecure-password elgato groups G1,G2 user xdb insecure-password hello groups G2 Please note that both lists are functionally identical. It is possible to synchronize server entries in stick tables between several haproxy instances over TCP connections in a multi-master fashion. Each instance pushes its local updates and insertions to remote peers. Server IDs are used to identify servers remotely, so it is important that configurations look similar or at least that the same IDs are forced on each server on all participants. Interrupted exchanges are automatically detected and recovered from the last known point. In addition, during a soft restart, the old process connects to the new one using such a TCP connection to push all its entries before the new process tries to connect to other peers. That ensures very fast replication during a reload, it typically takes a fraction of a second even for large tables. Creates a new peer list with name . It is an independent section, which is referenced by one or more stick-tables. Disables a peers section. It disables both listening and any synchronization related to this section. This is provided to disable synchronization of stick tables without having to comment out all “peers” references. This re-enables a disabled peers section which was previously disabled. peer :Defines a peer inside a peers section. If is set to the local peer name (by default hostname, or forced using “-L” command line option), haproxy will listen for incoming remote peer connection on :. Otherwise, : defines where to connect to to join the remote peer, and is used at the protocol level to identify and validate the remote peer on the server side. During a soft restart, local peer : is used by the old instance to connect the new one and initiate a complete replication (teaching process). It is strongly recommended to have the exact same peers declaration on all peers and to only rely on the “-L” command line argument to change the local peer name. This makes it easier to maintain coherent configuration files across all peers. Any part of the address string may reference any number of environment variables by preceding their name with a dollar sign (‘$’) and optionally enclosing them with braces (‘{}’), similarly to what is done in Bourne shell. Example: peers mypeers peer haproxy1 192.168.0.1:1024 peer haproxy2 192.168.0.2:1024 peer haproxy3 10.2.0.1:1024 backend mybackend mode tcp balance roundrobin stick-table type ip size 20k peers mypeers stick on src server srv1 192.168.0.30:80 server srv2 192.168.0.31:80 Proxy configuration can be located in a set of sections : – defaults – frontend – backend – listen A “defaults” section sets default parameters for all other sections following its declaration. Those default parameters are reset by the next “defaults” section. See below for the list of parameters which can be set in a “defaults” section. The name is optional but its use is encouraged for better readability. A “frontend” section describes a set of listening sockets accepting client connections. A “backend” section describes a set of servers to which the proxy will connect to forward incoming connections. A “listen” section defines a complete proxy with its frontend and backend parts combined in one section. It is generally useful for TCP-only traffic. All proxy names must be formed from upper and lower case letters, digits, ‘-‘ (dash), ‘_’ (underscore) , ‘.’ (dot) and ‘:’ (colon). ACL names are case-sensitive, which means that “www” and “WWW” are two different proxies. Historically, all proxy names could overlap, it just caused troubles in the logs. Since the introduction of content switching, it is mandatory that two proxies with overlapping capabilities (frontend/backend) have different names. However, it is still permitted that a frontend and a backend share the same name, as this configuration seems to be commonly encountered. Right now, two major proxy modes are supported : “tcp”, also known as layer 4, and “http”, also known as layer 7. In layer 4 mode, HAProxy simply forwards bidirectional traffic between two sides. In layer 7 mode, HAProxy analyzes the protocol, and can interact with it by allowing, blocking, switching, adding, modifying, or removing arbitrary contents in requests or responses, based on arbitrary criteria. In HTTP mode, the processing applied to requests and responses flowing over a connection depends in the combination of the frontend’s HTTP options and the backend’s. HAProxy supports 5 connection modes : – KAL : keep alive (“option http-keep-alive“) which is the default mode : all requests and responses are processed, and connections remain open but idle between responses and new requests. – TUN: tunnel (“option http-tunnel“) : this was the default mode for versions 1.0 to 1.5-dev21 : only the first request and response are processed, and everything else is forwarded with no analysis at all. This mode should not be used as it creates lots of trouble with logging and HTTP processing. – PCL: passive close (“option httpclose“) : exactly the same as tunnel mode, but with “Connection: close” appended in both directions to try to make both ends close after the first request/response exchange. – SCL: server close (“option http-server-close“) : the server-facing connection is closed after the end of the response is received, but the client-facing connection remains open. – FCL: forced close (“option forceclose“) : the connection is actively closed after the end of the response. The effective mode that will be applied to a connection passing through a frontend and a backend can be determined by both proxy modes according to the following matrix, but in short, the modes are symmetric, keep-alive is the weakest option and force close is the strongest. Backend mode | KAL | TUN | PCL | SCL | FCL —-+—–+—–+—–+—–+—- KAL | KAL | TUN | PCL | SCL | FCL —-+—–+—–+—–+—–+—- TUN | TUN | TUN | PCL | SCL | FCL Frontend —-+—–+—–+—–+—–+—- mode PCL | PCL | PCL | PCL | FCL | FCL —-+—–+—–+—–+—–+—- SCL | SCL | SCL | FCL | SCL | FCL —-+—–+—–+—–+—–+—- FCL | FCL | FCL | FCL | FCL | FCL

4.1. Proxy keywords matrix

The following list of keywords is supported. Most of them may only be used in a limited set of section types. Some of them are marked as “deprecated” because they are inherited from an old syntax which may be confusing or functionally limited, and there are new recommended keywords to replace them. Keywords marked with “(*)” can be optionally inverted using the “no” prefix, eg. “no option contstats”. This makes sense when the option has been enabled by default and must be disabled for a specific instance. Such options may also be prefixed with “default” in order to restore default settings regardless of what has been specified in a previous “defaults” section.

4.2. Alphabetically sorted keywords reference

This section provides a description of each keyword and its usage. acl [flags] [operator] …Declare or complete an access list.

May be used in sections :

defaults frontend listen backend

Example: acl invalid_src src 0.0.0.0/7 224.0.0.0/3 acl invalid_src src_port 0:1023 acl local_dst hdr(host) -i localhost See section 7 about ACL usage. appsession len timeout [request-learn] [prefix] [mode ]Define session stickiness on an existing application cookie.

May be used in sections :

defaults frontend listen backend

Arguments : this is the name of the cookie used by the application and which HAProxy will have to learn for each new session. this is the max number of characters that will be memorized and checked in each cookie value. this is the time after which the cookie will be removed from memory if unused. If no unit is specified, this time is in milliseconds. request-learn If this option is specified, then haproxy will be able to learn the cookie found in the request in case the server does not specify any in response. This is typically what happens with PHPSESSID cookies, or when haproxy’s session expires before the application’s session and the correct server is selected. It is recommended to specify this option to improve reliability. prefix When this option is specified, haproxy will match on the cookie prefix (or URL parameter prefix). The appsession value is the data following this prefix. Example : appsession ASPSESSIONID len 64 timeout 3h prefix This will match the cookie ASPSESSIONIDXXXX=XXXXX, the appsession value will be XXXX=XXXXX. mode This option allows to change the URL parser mode. 2 modes are currently supported : – path-parameters : The parser looks for the appsession in the path parameters part (each parameter is separated by a semi-colon), which is convenient for JSESSIONID for example. This is the default mode if the option is not set. – query-string : In this mode, the parser will look for the appsession in the query string. When an application cookie is defined in a backend, HAProxy will check when the server sets such a cookie, and will store its value in a table, and associate it with the server’s identifier. Up to characters from the value will be retained. On each connection, haproxy will look for this cookie both in the “Cookie:” headers, and as a URL parameter (depending on the mode used). If a known value is found, the client will be directed to the server associated with this value. Otherwise, the load balancing algorithm is applied. Cookies are automatically removed from memory when they have been unused for a duration longer than . The definition of an application cookie is limited to one per backend. Note : Consider not using this feature in multi-process mode (nbproc > 1) unless you know what you do : memory is not shared between the processes, which can result in random behaviours. Example : appsession JSESSIONID len 52 timeout 3h Give hints to the system about the approximate listen backlog desired size

May be used in sections :

defaults frontend listen backend

Arguments : is the number of pending connections. Depending on the operating system, it may represent the number of already acknowledged connections, of non-acknowledged ones, or both. In order to protect against SYN flood attacks, one solution is to increase the system’s SYN backlog size. Depending on the system, sometimes it is just tunable via a system parameter, sometimes it is not adjustable at all, and sometimes the system relies on hints given by the application at the time of the listen() syscall. By default, HAProxy passes the frontend’s maxconn value to the listen() syscall. On systems which can make use of this value, it can sometimes be useful to be able to specify a different value, hence this backlog parameter. On Linux 2.4, the parameter is ignored by the system. On Linux 2.6, it is used as a hint and the system accepts up to the smallest greater power of two, and never more than some limits (usually 32768). balance [ ]Define the load balancing algorithm to be used in a backend.

May be used in sections :

defaults frontend listen backend

Arguments : is the algorithm used to select a server when doing load balancing. This only applies when no persistence information is available, or when a connection is redispatched to another server. may be one of the following : roundrobin Each server is used in turns, according to their weights. This is the smoothest and fairest algorithm when the server’s processing time remains equally distributed. This algorithm is dynamic, which means that server weights may be adjusted on the fly for slow starts for instance. It is limited by design to 4095 active servers per backend. Note that in some large farms, when a server becomes up after having been down for a very short time, it may sometimes take a few hundreds requests for it to be re-integrated into the farm and start receiving traffic. This is normal, though very rare. It is indicated here in case you would have the chance to observe it, so that you don’t worry. static-rr Each server is used in turns, according to their weights. This algorithm is as similar to roundrobin except that it is static, which means that changing a server’s weight on the fly will have no effect. On the other hand, it has no design limitation on the number of servers, and when a server goes up, it is always immediately reintroduced into the farm, once the full map is recomputed. It also uses slightly less CPU to run (around -1%). leastconn The server with the lowest number of connections receives the connection. Round-robin is performed within groups of servers of the same load to ensure that all servers will be used. Use of this algorithm is recommended where very long sessions are expected, such as LDAP, SQL, TSE, etc… but is not very well suited for protocols using short sessions such as HTTP. This algorithm is dynamic, which means that server weights may be adjusted on the fly for slow starts for instance. first The first server with available connection slots receives the connection. The servers are chosen from the lowest numeric identifier to the highest (see server parameter “id“), which defaults to the server’s position in the farm. Once a server reaches its maxconn value, the next server is used. It does not make sense to use this algorithm without setting maxconn. The purpose of this algorithm is to always use the smallest number of servers so that extra servers can be powered off during non-intensive hours. This algorithm ignores the server weight, and brings more benefit to long session such as RDP or IMAP than HTTP, though it can be useful there too. In order to use this algorithm efficiently, it is recommended that a cloud controller regularly checks server usage to turn them off when unused, and regularly checks backend queue to turn new servers on when the queue inflates. Alternatively, using “http-check send-state” may inform servers on the load. source The source IP address is hashed and divided by the total weight of the running servers to designate which server will receive the request. This ensures that the same client IP address will always reach the same server as long as no server goes down or up. If the hash result changes due to the number of running servers changing, many clients will be directed to a different server. This algorithm is generally used in TCP mode where no cookie may be inserted. It may also be used on the Internet to provide a best-effort stickiness to clients which refuse session cookies. This algorithm is static by default, which means that changing a server’s weight on the fly will have no effect, but this can be changed using “hash-type“. uri This algorithm hashes either the left part of the URI (before the question mark) or the whole URI (if the “whole” parameter is present) and divides the hash value by the total weight of the running servers. The result designates which server will receive the request. This ensures that the same URI will always be directed to the same server as long as no server goes up or down. This is used with proxy caches and anti-virus proxies in order to maximize the cache hit rate. Note that this algorithm may only be used in an HTTP backend. This algorithm is static by default, which means that changing a server’s weight on the fly will have no effect, but this can be changed using “hash-type“. This algorithm supports two optional parameters “len” and “depth”, both followed by a positive integer number. These options may be helpful when it is needed to balance servers based on the beginning of the URI only. The “len” parameter indicates that the algorithm should only consider that many characters at the beginning of the URI to compute the hash. Note that having “len” set to 1 rarely makes sense since most URIs start with a leading “/”. The “depth” parameter indicates the maximum directory depth to be used to compute the hash. One level is counted for each slash in the request. If both parameters are specified, the evaluation stops when either is reached. url_param The URL parameter specified in argument will be looked up in the query string of each HTTP GET request. If the modifier “check_post” is used, then an HTTP POST request entity will be searched for the parameter argument, when it is not found in a query string after a question mark (‘?’) in the URL. The message body will only start to be analyzed once either the advertised amount of data has been received or the request buffer is full. In the unlikely event that chunked encoding is used, only the first chunk is scanned. Parameter values separated by a chunk boundary, may be randomly balanced if at all. This keyword used to support an optional parameter which is now ignored. If the parameter is found followed by an equal sign (‘=’) and a value, then the value is hashed and divided by the total weight of the running servers. The result designates which server will receive the request. This is used to track user identifiers in requests and ensure that a same user ID will always be sent to the same server as long as no server goes up or down. If no value is found or if the parameter is not found, then a round robin algorithm is applied. Note that this algorithm may only be used in an HTTP backend. This algorithm is static by default, which means that changing a server’s weight on the fly will have no effect, but this can be changed using “hash-type“. hdr() The HTTP header will be looked up in each HTTP request. Just as with the equivalent ACL ‘hdr()’ function, the header name in parenthesis is not case sensitive. If the header is absent or if it does not contain any value, the roundrobin algorithm is applied instead. An optional ‘use_domain_only’ parameter is available, for reducing the hash algorithm to the main domain part with some specific headers such as ‘Host’. For instance, in the Host value “haproxy.1wt.eu”, only “1wt” will be considered. This algorithm is static by default, which means that changing a server’s weight on the fly will have no effect, but this can be changed using “hash-type“. rdp-cookie rdp-cookie() The RDP cookie (or “mstshash” if omitted) will be looked up and hashed for each incoming TCP request. Just as with the equivalent ACL ‘req_rdp_cookie()’ function, the name is not case-sensitive. This mechanism is useful as a degraded persistence mode, as it makes it possible to always send the same user (or the same session ID) to the same server. If the cookie is not found, the normal roundrobin algorithm is used instead. Note that for this to work, the frontend must ensure that an RDP cookie is already present in the request buffer. For this you must use ‘tcp-request content accept’ rule combined with a ‘req_rdp_cookie_cnt’ ACL. This algorithm is static by default, which means that changing a server’s weight on the fly will have no effect, but this can be changed using “hash-type“. See also the rdp_cookie pattern fetch function. is an optional list of arguments which may be needed by some algorithms. Right now, only “url_param” and “uri” support an optional argument. The load balancing algorithm of a backend is set to roundrobin when no other algorithm, mode nor option have been set. The algorithm may only be set once for each backend. Examples : balance roundrobin balance url_param userid balance url_param session_id check_post 64 balance hdr(User-Agent) balance hdr(host) balance hdr(Host) use_domain_only Note: the following caveats and limitations on using the “check_post” extension with “url_param” must be considered : – all POST requests are eligible for consideration, because there is no way to determine if the parameters will be found in the body or entity which may contain binary data. Therefore another method may be required to restrict consideration of POST requests that have no URL parameters in the body. (see acl reqideny http_end) – using a value larger than the request buffer size does not make sense and is useless. The buffer size is set at build time, and defaults to 16 kB. – Content-Encoding is not supported, the parameter search will probably fail; and load balancing will fall back to Round Robin. – Expect: 100-continue is not supported, load balancing will fall back to Round Robin. – Transfer-Encoding (RFC2616 3.6.1) is only supported in the first chunk. If the entire parameter value is not present in the first chunk, the selection of server is undefined (actually, defined by how little actually appeared in the first chunk). – This feature does not support generation of a 100, 411 or 501 response. – In some cases, requesting “check_post” MAY attempt to scan the entire contents of a message body. Scanning normally terminates when linear white space or control characters are found, indicating the end of what might be a URL parameter list. This is probably not a concern with SGML type message bodies. bind [

]: [, …] [param*]bind / [, …] [param*]Define one or several listening addresses and/or ports in a frontend.

May be used in sections :

defaults frontend listen backend

Arguments :

is optional and can be a host name, an IPv4 address, an IPv6 address, or ‘*’. It designates the address the frontend will listen on. If unset, all IPv4 addresses of the system will be listened on. The same will apply for ‘*’ or the system’s special address “0.0.0.0”. The IPv6 equivalent is ‘::’. Optionally, an address family prefix may be used before the address to force the family regardless of the address format, which can be useful to specify a path to a unix socket with no slash (‘/’). Currently supported prefixes are : – ‘ipv4@’ -> address is always IPv4 – ‘ipv6@’ -> address is always IPv6 – ‘unix@’ -> address is a path to a local unix socket – ‘abns@’ -> address is in abstract namespace (Linux only). Note: since abstract sockets are not “rebindable”, they do not cope well with multi-process mode during soft-restart, so it is better to avoid them if nbproc is greater than 1. The effect is that if the new process fails to start, only one of the old ones will be able to rebind to the socket. – ‘fd@‘ -> use file descriptor inherited from the parent. The fd must be bound and may or may not already be listening. Any part of the address string may reference any number of environment variables by preceding their name with a dollar sign (‘$’) and optionally enclosing them with braces (‘{}’), similarly to what is done in Bourne shell. is either a unique TCP port, or a port range for which the proxy will accept connections for the IP address specified above. The port is mandatory for TCP listeners. Note that in the case of an IPv6 address, the port is always the number after the last colon (‘:’). A range can either be : – a numerical port (ex: ’80’) – a dash-delimited ports range explicitly stating the lower and upper bounds (ex: ‘2000-2100’) which are included in the range. Particular care must be taken against port ranges, because every couple consumes one socket (= a file descriptor), so it’s easy to consume lots of descriptors with a simple range, and to run out of sockets. Also, each couple must be used only once among all instances running on a same system. Please note that binding to ports lower than 1024 generally require particular privileges to start the program, which are independent of the ‘uid’ parameter. is a UNIX socket path beginning with a slash (‘/’). This is alternative to the TCP listening port. Haproxy will then receive UNIX connections on the socket located at this place. The path must begin with a slash and by default is absolute. It can be relative to the prefix defined by “unix-bind” in the global section. Note that the total length of the prefix followed by the socket path cannot exceed some system limits for UNIX sockets, which commonly are set to 107 characters. is a list of parameters common to all sockets declared on the same line. These numerous parameters depend on OS and build options and have a complete section dedicated to them. Please refer to section 5 to for more details. It is possible to specify a list of address:port combinations delimited by commas. The frontend will then listen on all of these addresses. There is no fixed limit to the number of addresses and ports which can be listened on in a frontend, as well as there is no limit to the number of “bind” statements in a frontend. Example : listen http_proxy bind :80,:443 bind 10.0.0.1:10080,10.0.0.1:10443 bind /var/run/ssl-frontend.sock user root mode 600 accept-proxy listen http_https_proxy bind :80 bind :443 ssl crt /etc/haproxy/site.pem listen http_https_proxy_explicit bind ipv6@:80 bind ipv4@public_ssl:443 ssl crt /etc/haproxy/site.pem bind unix@ssl-frontend.sock user root mode 600 accept-proxy listen external_bind_app1 bind fd@${FD_APP1} Note: regarding Linux’s abstract namespace sockets, HAProxy uses the whole sun_path length is used for the address length. Some other programs such as socat use the string length only by default. Pass the option “,unix-tightsocklen=0” to any abstract socket definition in socat to make it compatible with HAProxy’s. bind-process [ all | odd | even | [-] ] …Limit visibility of an instance to a certain set of processes numbers.

May be used in sections :

defaults frontend listen backend

Arguments :all All process will see this instance. This is the default. It may be used to override a default value. odd This instance will be enabled on processes 1,3,5,…63. This option may be combined with other numbers. even This instance will be enabled on processes 2,4,6,…64. This option may be combined with other numbers. Do not use it with less than 2 processes otherwise some instances might be missing from all processes. number The instance will be enabled on this process number or range, whose values must all be between 1 and 32 or 64 depending on the machine’s word size. If a proxy is bound to process numbers greater than the configured global.nbproc, it will either be forced to process #1 if a single process was specified, or to all processes otherwise. This keyword limits binding of certain instances to certain processes. This is useful in order not to have too many processes listening to the same ports. For instance, on a dual-core machine, it might make sense to set ‘nbproc 2’ in the global section, then distributes the listeners among ‘odd’ and ‘even’ instances. At the moment, it is not possible to reference more than 32 or 64 processes using this keyword, but this should be more than enough for most setups. Please note that ‘all’ really means all processes regardless of the machine’s word size, and is not limited to the first 32 or 64. Each “bind” line may further be limited to a subset of the proxy’s processes, please consult the “process” bind keyword in section 5.1. When a frontend has no explicit “bind-process” line, it tries to bind to all the processes referenced by its “bind” lines. That means that frontends can easily adapt to their listeners’ processes. If some backends are referenced by frontends bound to other processes, the backend automatically inherits the frontend’s processes. Example : listen app_ip1 bind 10.0.0.1:80 bind-process odd listen app_ip2 bind 10.0.0.2:80 bind-process even listen management bind 10.0.0.3:80 bind-process 1 2 3 4 listen management bind 10.0.0.4:80 bind-process 1-4 block { if | unless } Block a layer 7 request if/unless a condition is matched

May be used in sections :

defaults frontend listen backend

The HTTP request will be blocked very early in the layer 7 processing if/unless is matched. A 403 error will be returned if the request is blocked. The condition has to reference ACLs (see section 7). This is typically used to deny access to certain sensitive resources if some conditions are met or not met. There is no fixed limit to the number of “block” statements per instance. Example: acl invalid_src src 0.0.0.0/7 224.0.0.0/3 acl invalid_src src_port 0:1023 acl local_dst hdr(host) -i localhost block if invalid_src || local_dst See section 7 about ACL usage. Capture and log a cookie in the request and in the response.

May be used in sections :

defaults frontend listen backend

Arguments : is the beginning of the name of the cookie to capture. In order to match the exact name, simply suffix the name with an equal sign (‘=’). The full name will appear in the logs, which is useful with application servers which adjust both the cookie name and value (eg: ASPSESSIONXXXXX). is the maximum number of characters to report in the logs, which include the cookie name, the equal sign and the value, all in the standard “name=value” form. The string will be truncated on the right if it exceeds . Only the first cookie is captured. Both the “cookie” request headers and the “set-cookie” response headers are monitored. This is particularly useful to check for application bugs causing session crossing or stealing between users, because generally the user’s cookies can only change on a login page. When the cookie was not presented by the client, the associated log column will report “-“. When a request does not cause a cookie to be assigned by the server, a “-” is reported in the response column. The capture is performed in the frontend only because it is necessary that the log format does not change for a given frontend depending on the backends. This may change in the future. Note that there can be only one “capture cookie” statement in a frontend. The maximum capture length is set by the global “tune.http.cookielen” setting and defaults to 63 characters. It is not possible to specify a capture in a “defaults” section. Example: capture cookie ASPSESSION len 32 Capture and log the last occurrence of the specified request header.

May be used in sections :

defaults frontend listen backend

Arguments : is the name of the header to capture. The header names are not case-sensitive, but it is a common practice to write them as they appear in the requests, with the first letter of each word in upper case. The header name will not appear in the logs, only the value is reported, but the position in the logs is respected. is the maximum number of characters to extract from the value and report in the logs. The string will be truncated on the right if it exceeds . The complete value of the last occurrence of the header is captured. The value will be added to the logs between braces (‘{}’). If multiple headers are captured, they will be delimited by a vertical bar (‘|’) and will appear in the same order they were declared in the configuration. Non-existent headers will be logged just as an empty string. Common uses for request header captures include the “Host” field in virtual hosting environments, the “Content-length” when uploads are supported, “User-agent” to quickly differentiate between real users and robots, and “X-Forwarded-For” in proxied environments to find where the request came from. Note that when capturing headers such as “User-agent”, some spaces may be logged, making the log analysis more difficult. Thus be careful about what you log if you know your log parser is not smart enough to rely on the braces. There is no limit to the number of captured request headers nor to their length, though it is wise to keep them low to limit memory usage per session. In order to keep log format consistent for a same frontend, header captures can only be declared in a frontend. It is not possible to specify a capture in a “defaults” section. Example: capture request header Host len 15 capture request header X-Forwarded-For len 15 capture request header Referer len 15 Capture and log the last occurrence of the specified response header.

May be used in sections :

defaults frontend listen backend

Arguments : is the name of the header to capture. The header names are not case-sensitive, but it is a common practice to write them as they appear in the response, with the first letter of each word in upper case. The header name will not appear in the logs, only the value is reported, but the position in the logs is respected. is the maximum number of characters to extract from the value and report in the logs. The string will be truncated on the right if it exceeds . The complete value of the last occurrence of the header is captured. The result will be added to the logs between braces (‘{}’) after the captured request headers. If multiple headers are captured, they will be delimited by a vertical bar (‘|’) and will appear in the same order they were declared in the configuration. Non-existent headers will be logged just as an empty string. Common uses for response header captures include the “Content-length” header which indicates how many bytes are expected to be returned, the “Location” header to track redirections. There is no limit to the number of captured response headers nor to their length, though it is wise to keep them low to limit memory usage per session. In order to keep log format consistent for a same frontend, header captures can only be declared in a frontend. It is not possible to specify a capture in a “defaults” section. Example: capture response header Content-length len 9 capture response header Location len 15 Set the maximum inactivity time on the client side.

May be used in sections :

defaults frontend listen backend

Arguments : is the timeout value is specified in milliseconds by default, but can be in any other unit if the number is suffixed by the unit, as explained at the top of this document. The inactivity timeout applies when the client is expected to acknowledge or send data. In HTTP mode, this timeout is particularly important to consider during the first phase, when the client sends the request, and during the response while it is reading data sent by the server. The value is specified in milliseconds by default, but can be in any other unit if the number is suffixed by the unit, as specified at the top of this document. In TCP mode (and to a lesser extent, in HTTP mode), it is highly recommended that the client timeout remains equal to the server timeout in order to avoid complex situations to debug. It is a good practice to cover one or several TCP packet losses by specifying timeouts that are slightly above multiples of 3 seconds (eg: 4 or 5 seconds). This parameter is specific to frontends, but can be specified once for all in “defaults” sections. This is in fact one of the easiest solutions not to forget about it. An unspecified timeout results in an infinite timeout, which is not recommended. Such a usage is accepted and works but reports a warning during startup because it may results in accumulation of expired sessions in the system if the system’s timeouts are not configured either. This parameter is provided for compatibility but is currently deprecated. Please use “timeout client” instead. Enable HTTP compression.

May be used in sections :

defaults frontend listen backend

Arguments :algo is followed by the list of supported compression algorithms. type is followed by the list of MIME types that will be compressed. offload makes haproxy work as a compression offloader only (see notes). The currently supported algorithms are : identity this is mostly for debugging, and it was useful for developing the compression feature. Identity does not apply any change on data. gzip applies gzip compression. This setting is only available when support for zlib was built in. deflate same as gzip, but with deflate algorithm and zlib format. Note that this algorithm has ambiguous support on many browsers and no support at all from recent ones. It is strongly recommended not to use it for anything else than experimentation. This setting is only available when support for zlib was built in. Compression will be activated depending on the Accept-Encoding request header. With identity, it does not take care of that header. If backend servers support HTTP compression, these directives will be no-op: haproxy will see the compressed response and will not compress again. If backend servers do not support HTTP compression and there is Accept-Encoding header in request, haproxy will compress the matching response. The “offload” setting makes haproxy remove the Accept-Encoding header to prevent backend servers from compressing responses. It is strongly recommended not to do this because this means that all the compression work will be done on the single point where haproxy is located. However in some deployment scenarios, haproxy may be installed in front of a buggy gateway with broken HTTP compression implementation which can’t be turned off. In that case haproxy can be used to prevent that gateway from emitting invalid payloads. In this case, simply removing the header in the configuration does not work because it applies before the header is parsed, so that prevents haproxy from compressing. The “offload” setting should then be used for such scenarios. Note: for now, the “offload” setting is ignored when set in a defaults section. Compression is disabled when: * the request does not advertise a supported compression algorithm in the “Accept-Encoding” header * the response message is not HTTP/1.1 * HTTP status code is not 200 * response header “Transfer-Encoding” contains “chunked” (Temporary Workaround) * response contain neither a “Content-Length” header nor a “Transfer-Encoding” whose last value is “chunked” * response contains a “Content-Type” header whose first value starts with “multipart” * the response contains the “no-transform” value in the “Cache-control” header * User-Agent matches “Mozilla/4” unless it is MSIE 6 with XP SP2, or MSIE 7 and later * The response contains a “Content-Encoding” header, indicating that the response is already compressed (see compression offload) Note: The compression does not rewrite Etag headers, and does not emit the Warning header. Examples : compression algo gzip compression type text/html text/plain Set the maximum time to wait for a connection attempt to a server to succeed.

May be used in sections :

defaults frontend listen backend

Arguments : is the timeout value is specified in milliseconds by default, but can be in any other unit if the number is suffixed by the unit, as explained at the top of this document. If the server is located on the same LAN as haproxy, the connection should be immediate (less than a few milliseconds). Anyway, it is a good practice to cover one or several TCP packet losses by specifying timeouts that are slightly above multiples of 3 seconds (eg: 4 or 5 seconds). By default, the connect timeout also presets the queue timeout to the same value if this one has not been specified. Historically, the contimeout was also used to set the tarpit timeout in a listen section, which is not possible in a pure frontend. This parameter is specific to backends, but can be specified once for all in “defaults” sections. This is in fact one of the easiest solutions not to forget about it. An unspecified timeout results in an infinite timeout, which is not recommended. Such a usage is accepted and works but reports a warning during startup because it may results in accumulation of failed sessions in the system if the system’s timeouts are not configured either. This parameter is provided for backwards compatibility but is currently deprecated. Please use “timeout connect“, “timeout queue” or “timeout tarpit” instead. cookie [ rewrite | insert | prefix ] [ indirect ] [ nocache ] [ postonly ] [ preserve ] [ httponly ] [ secure ] [ domain ]* [ maxidle ] [ maxlife ]Enable cookie-based persistence in a backend.

May be used in sections :

defaults frontend listen backend

Arguments : is the name of the cookie which will be monitored, modified or inserted in order to bring persistence. This cookie is sent to the client via a “Set-Cookie” header in the response, and is brought back by the client in a “Cookie” header in all requests. Special care should be taken to choose a name which does not conflict with any likely application cookie. Also, if the same backends are subject to be used by the same clients (eg: HTTP/HTTPS), care should be taken to use different cookie names between all backends if persistence between them is not desired. rewrite This keyword indicates that the cookie will be provided by the server and that haproxy will have to modify its value to set the server’s identifier in it. This mode is handy when the management of complex combinations of “Set-cookie” and “Cache-control” headers is left to the application. The application can then decide whether or not it is appropriate to emit a persistence cookie. Since all responses should be monitored, this mode doesn’t work in HTTP tunnel mode. Unless the application behaviour is very complex and/or broken, it is advised not to start with this mode for new deployments. This keyword is incompatible with “insert” and “prefix”. insert This keyword indicates that the persistence cookie will have to be inserted by haproxy in server responses if the client did not already have a cookie that would have permitted it to access this server. When used without the “preserve” option, if the server emits a cookie with the same name, it will be remove before processing. For this reason, this mode can be used to upgrade existing configurations running in the “rewrite” mode. The cookie will only be a session cookie and will not be stored on the client’s disk. By default, unless the “indirect” option is added, the server will see the cookies emitted by the client. Due to caching effects, it is generally wise to add the “nocache” or “postonly” keywords (see below). The “insert” keyword is not compatible with “rewrite” and “prefix”. prefix This keyword indicates that instead of relying on a dedicated cookie for the persistence, an existing one will be completed. This may be needed in some specific environments where the client does not support more than one single cookie and the application already needs it. In this case, whenever the server sets a cookie named , it will be prefixed with the server’s identifier and a delimiter. The prefix will be removed from all client requests so that the server still finds the cookie it emitted. Since all requests and responses are subject to being modified, this mode doesn’t work with tunnel mode. The “prefix” keyword is not compatible with “rewrite” and “insert”. Note: it is highly recommended not to use “indirect” with “prefix”, otherwise server cookie updates would not be sent to clients. indirect When this option is specified, no cookie will be emitted to a client which already has a valid one for the server which has processed the request. If the server sets such a cookie itself, it will be removed, unless the “preserve” option is also set. In “insert” mode, this will additionally remove cookies from the requests transmitted to the server, making the persistence mechanism totally transparent from an application point of view. Note: it is highly recommended not to use “indirect” with “prefix”, otherwise server cookie updates would not be sent to clients. nocache This option is recommended in conjunction with the insert mode when there is a cache between the client and HAProxy, as it ensures that a cacheable response will be tagged non-cacheable if a cookie needs to be inserted. This is important because if all persistence cookies are added on a cacheable home page for instance, then all customers will then fetch the page from an outer cache and will all share the same persistence cookie, leading to one server receiving much more traffic than others. See also the “insert” and “postonly” options. postonly This option ensures that cookie insertion will only be performed on responses to POST requests. It is an alternative to the “nocache” option, because POST responses are not cacheable, so this ensures that the persistence cookie will never get cached. Since most sites do not need any sort of persistence before the first POST which generally is a login request, this is a very efficient method to optimize caching without risking to find a persistence cookie in the cache. See also the “insert” and “nocache” options. preserve This option may only be used with “insert” and/or “indirect”. It allows the server to emit the persistence cookie itself. In this case, if a cookie is found in the response, haproxy will leave it untouched. This is useful in order to end persistence after a logout request for instance. For this, the server just has to emit a cookie with an invalid value (eg: empty) or with a date in the past. By combining this mechanism with the “disable-on-404” check option, it is possible to perform a completely graceful shutdown because users will definitely leave the server after they logout. httponly This option tells haproxy to add an “HttpOnly” cookie attribute when a cookie is inserted. This attribute is used so that a user agent doesn’t share the cookie with non-HTTP components. Please check RFC6265 for more information on this attribute. secure This option tells haproxy to add a “Secure” cookie attribute when a cookie is inserted. This attribute is used so that a user agent never emits this cookie over non-secure channels, which means that a cookie learned with this flag will be presented only over SSL/TLS connections. Please check RFC6265 for more information on this attribute. domain This option allows to specify the domain at which a cookie is inserted. It requires exactly one parameter: a valid domain name. If the domain begins with a dot, the browser is allowed to use it for any host ending with that name. It is also possible to specify several domain names by invoking this option multiple times. Some browsers might have small limits on the number of domains, so be careful when doing that. For the record, sending 10 domains to MSIE 6 or Firefox 2 works as expected. maxidle This option allows inserted cookies to be ignored after some idle time. It only works with insert-mode cookies. When a cookie is sent to the client, the date this cookie was emitted is sent too. Upon further presentations of this cookie, if the date is older than the delay indicated by the parameter (in seconds), it will be ignored. Otherwise, it will be refreshed if needed when the response is sent to the client. This is particularly useful to prevent users who never close their browsers from remaining for too long on the same server (eg: after a farm size change). When this option is set and a cookie has no date, it is always accepted, but gets refreshed in the response. This maintains the ability for admins to access their sites. Cookies that have a date in the future further than 24 hours are ignored. Doing so lets admins fix timezone issues without risking kicking users off the site. maxlife This option allows inserted cookies to be ignored after some life time, whether they’re in use or not. It only works with insert mode cookies. When a cookie is first sent to the client, the date this cookie was emitted is sent too. Upon further presentations of this cookie, if the date is older than the delay indicated by the parameter (in seconds), it will be ignored. If the cookie in the request has no date, it is accepted and a date will be set. Cookies that have a date in the future further than 24 hours are ignored. Doing so lets admins fix timezone issues without risking kicking users off the site. Contrary to maxidle, this value is not refreshed, only the first visit date counts. Both maxidle and maxlife may be used at the time. This is particularly useful to prevent users who never close their browsers from remaining for too long on the same server (eg: after a farm size change). This is stronger than the maxidle method in that it forces a redispatch after some absolute delay. There can be only one persistence cookie per HTTP backend, and it can be declared in a defaults section. The value of the cookie will be the value indicated after the “cookie” keyword in a “server” statement. If no cookie is declared for a given server, the cookie is not set. Examples : cookie JSESSIONID prefix cookie SRV insert indirect nocache cookie SRV insert postonly indirect cookie SRV insert indirect nocache maxidle 30m maxlife 8h Change default options for a server in a backend

May be used in sections :

defaults frontend listen backend

Arguments: is a list of parameters for this server. The “default-server” keyword accepts an important number of options and has a complete section dedicated to it. Please refer to section 5 for more details. Example : default-server inter 1000 weight 13 Specify the backend to use when no “use_backend” rule has been matched.

May be used in sections :

defaults frontend listen backend

Arguments : is the name of the backend to use. When doing content-switching between frontend and backends using the “use_backend” keyword, it is often useful to indicate which backend will be used when no rule has matched. It generally is the dynamic backend which will catch all undetermined requests. Example : use_backend dynamic if url_dyn use_backend static if url_css url_img extension_img default_backend dynamic Describe a listen, frontend or backend.

May be used in sections :

defaults frontend listen backend

Arguments : string

Allows to add a sentence to describe the related object in the HAProxy HTML stats page. The description will be printed on the right of the object name it describes. No need to backslash spaces in the arguments. Disable a proxy, frontend or backend.

May be used in sections :

defaults frontend listen backend

Arguments : none

The “disabled” keyword is used to disable an instance, mainly in order to liberate a listening port or to temporarily disable a service. The instance will still be created and its configuration will be checked, but it will be created in the “stopped” state and will appear as such in the statistics. It will not receive any traffic nor will it send any health-checks or logs. It is possible to disable many instances at once by adding the “disabled” keyword in a “defaults” section. Set a default server address

May be used in sections :

defaults frontend listen backend

Arguments :

is the IPv4 address of the default server. Alternatively, a resolvable hostname is supported, but this name will be resolved during start-up. is a mandatory port specification. All connections will be sent to this port, and it is not permitted to use port offsets as is possible with normal servers. The “dispatch” keyword designates a default server for use when no other server can take the connection. In the past it was used to forward non persistent connections to an auxiliary load balancer. Due to its simple syntax, it has also been used for simple TCP relays. It is recommended not to use it for more clarity, and to use the “server” directive instead. Enable a proxy, frontend or backend.

May be used in sections :

defaults frontend listen backend

Arguments : none

The “enabled” keyword is used to explicitly enable an instance, when the defaults has been set to “disabled“. This is very rarely used. Return a file contents instead of errors generated by HAProxy

May be used in sections :

defaults frontend listen backend

Arguments : is the HTTP status code. Currently, HAProxy is capable of generating codes 200, 400, 403, 408, 500, 502, 503, and 504. designates a file containing the full HTTP response. It is recommended to follow the common practice of appending ".http" to the filename so that people do not confuse the response with HTML error pages, and to use absolute paths, since files are read before any chroot is performed. It is important to understand that this keyword is not meant to rewrite errors returned by the server, but errors detected and returned by HAProxy. This is why the list of supported errors is limited to a small set. Code 200 is emitted in response to requests matching a "monitor-uri" rule. The files are returned verbatim on the TCP socket. This allows any trick such as redirections to another URL or site, as well as tricks to clean cookies, force enable or disable caching, etc... The package provides default error files returning the same contents as default errors. The files should not exceed the configured buffer size (BUFSIZE), which generally is 8 or 16 kB, otherwise they will be truncated. It is also wise not to put any reference to local contents (eg: images) in order to avoid loops between the client and HAProxy when all servers are down, causing an error to be returned instead of an image. For better HTTP compliance, it is recommended that all header lines end with CR-LF and not LF alone. The files are read at the same time as the configuration and kept in memory. For this reason, the errors continue to be returned even when the process is chrooted, and no file change is considered while the process is running. A simple method for developing those files consists in associating them to the 403 status code and interrogating a blocked URL. Example : errorfile 400 /etc/haproxy/errorfiles/400badreq.http errorfile 408 /dev/null errorfile 403 /etc/haproxy/errorfiles/403forbid.http errorfile 503 /etc/haproxy/errorfiles/503sorry.http Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in sections :

defaults frontend listen backend

Arguments : is the HTTP status code. Currently, HAProxy is capable of generating codes 200, 400, 403, 408, 500, 502, 503, and 504. it is the exact contents of the "Location" header. It may contain either a relative URI to an error page hosted on the same site, or an absolute URI designating an error page on another site. Special care should be given to relative URIs to avoid redirect loops if the URI itself may generate the same error (eg: 500). It is important to understand that this keyword is not meant to rewrite errors returned by the server, but errors detected and returned by HAProxy. This is why the list of supported errors is limited to a small set. Code 200 is emitted in response to requests matching a "monitor-uri" rule. Note that both keyword return the HTTP 302 status code, which tells the client to fetch the designated URL using the same HTTP method. This can be quite problematic in case of non-GET methods such as POST, because the URL sent to the client might not be allowed for something other than GET. To workaround this problem, please use "errorloc303" which send the HTTP 303 status code, indicating to the client that the URL must be fetched with a GET request. Return an HTTP redirection to a URL instead of errors generated by HAProxy

May be used in sections :

defaults frontend listen backend

Arguments : is the HTTP status code. Currently, HAProxy is capable of generating codes 400, 403, 408, 500, 502, 503, and 504. it is the exact contents of the "Location" header. It may contain either a relative URI to an error page hosted on the same site, or an absolute URI designating an error page on another site. Special care should be given to relative URIs to avoid redirect loops if the URI itself may generate the same error (eg: 500). It is important to understand that this keyword is not meant to rewrite errors returned by the server, but errors detected and returned by HAProxy. This is why the list of supported errors is limited to a small set. Code 200 is emitted in response to requests matching a "monitor-uri" rule. Note that both keyword return the HTTP 303 status code, which tells the client to fetch the designated URL using the same HTTP GET method. This solves the usual problems associated with "errorloc" and the 302 code. It is possible that some very old browsers designed before HTTP/1.1 do not support it, but no such problem has been reported till now. Declare a condition to force persistence on down servers

May be used in sections :

defaults frontend listen backend

By default, requests are not dispatched to down servers. It is possible to force this using "option persist", but it is unconditional and redispatches to a valid server if "option redispatch" is set. That leaves with very little possibilities to force some requests to reach a server which is artificially marked down for maintenance operations. The "force-persist" statement allows one to declare various ACL-based conditions which, when met, will cause a request to ignore the down status of a server and still try to connect to it. That makes it possible to start a server, still replying an error to the health checks, and run a specially configured browser to test the service. Among the handy methods, one could use a specific source IP address, or a specific cookie. The cookie also has the advantage that it can easily be added/removed on the browser from a test page. Once the service is validated, it is then possible to open the service to the world by returning a valid response to health checks. The forced persistence is enabled when an "if" condition is met, or unless an "unless" condition is met. The final redispatch is always disabled when this is used. Specify at what backend load the servers will reach their maxconn

May be used in sections :

defaults frontend listen backend

Arguments : is the number of connections on the backend which will make the servers use the maximal number of connections. When a server has a "maxconn" parameter specified, it means that its number of concurrent connections will never go higher. Additionally, if it has a "minconn" parameter, it indicates a dynamic limit following the backend's load. The server will then always accept at least connections, never more than , and the limit will be on the ramp between both values when the backend has less than concurrent connections. This makes it possible to limit the load on the servers during normal loads, but push it further for important loads without overloading the servers during exceptional loads. Since it's hard to get this value right, haproxy automatically sets it to 10% of the sum of the maxconns of all frontends that may branch to this backend (based on "use_backend" and "default_backend" rules). That way it's safe to leave it unset. However, "use_backend" involving dynamic names are not counted since there is no way to know if they could match or not. Example : backend dynamic fullconn 10000 server srv1 dyn1:80 minconn 100 maxconn 1000 server srv2 dyn2:80 minconn 100 maxconn 1000 Maintain a proxy operational for some time after a soft stop

May be used in sections :

defaults frontend listen backend

Arguments :

May be used in sections :

defaults frontend listen backend

Arguments : is the method used to select a server from the hash computed by the : map-based the hash table is a static array containing all alive servers. The hashes will be very smooth, will consider weights, but will be static in that weight changes while a server is up will be ignored. This means that there will be no slow start. Also, since a server is selected by its position in the array, most mappings are changed when the server count changes. This means that when a server goes up or down, or when a server is added to a farm, most connections will be redistributed to different servers. This can be inconvenient with caches for instance. consistent the hash table is a tree filled with many occurrences of each server. The hash key is looked up in the tree and the closest server is chosen. This hash is dynamic, it supports changing weights while the servers are up, so it is compatible with the slow start feature. It has the advantage that when a server goes up or down, only its associations are moved. When a server is added to the farm, only a few part of the mappings are redistributed, making it an ideal method for caches. However, due to its principle, the distribution will never be very smooth and it may sometimes be necessary to adjust a server's weight or its ID to get a more balanced distribution. In order to get the same distribution on multiple load balancers, it is important that all servers have the exact same IDs. Note: consistent hash uses sdbm and avalanche if no hash function is specified. is the hash function to be used : sdbm this function was created initially for sdbm (a public-domain reimplementation of ndbm) database library. It was found to do well in scrambling bits, causing better distribution of the keys and fewer splits. It also happens to be a good general hashing function with good distribution, unless the total server weight is a multiple of 64, in which case applying the avalanche modifier may help. djb2 this function was first proposed by Dan Bernstein many years ago on comp.lang.c. Studies have shown that for certain workload this function provides a better distribution than sdbm. It generally works well with text-based inputs though it can perform extremely poorly with numeric-only input or when the total server weight is a multiple of 33, unless the avalanche modifier is also used. wt6 this function was designed for haproxy while testing other functions in the past. It is not as smooth as the other ones, but is much less sensible to the input data set or to the number of servers. It can make sense as an alternative to sdbm+avalanche or djb2+avalanche for consistent hashing or when hashing on numeric data such as a source IP address or a visitor identifier in a URL parameter. indicates an optional method applied after hashing the key : avalanche This directive indicates that the result from the hash function above should not be used in its raw form but that a 4-byte full avalanche hash must be applied first. The purpose of this step is to mix the resulting bits from the previous hash in order to avoid any undesired effect when the input contains some limited values or when the number of servers is a multiple of one of the hash's components (64 for SDBM, 33 for DJB2). Enabling avalanche tends to make the result less predictable, but it's also not as smooth as when using the original function. Some testing might be needed with some workloads. This hash is one of the many proposed by Bob Jenkins. The default hash type is "map-based" and is recommended for most usages. The default function is "sdbm", the selection of a function should be based on the range of the values being hashed. Enable a maintenance mode upon HTTP/404 response to health-checks

May be used in sections :

defaults frontend listen backend

Arguments : none

When this option is set, a server which returns an HTTP code 404 will be excluded from further load-balancing, but will still receive persistent connections. This provides a very convenient method for Web administrators to perform a graceful shutdown of their servers. It is also important to note that a server which is detected as failed while it was in this mode will not generate an alert, just a notice. If the server responds 2xx or 3xx again, it will immediately be reinserted into the farm. The status on the stats page reports "NOLB" for a server in this mode. It is important to note that this option only works in conjunction with the "httpchk" option. If this option is used with "http-check expect", then it has precedence over it so that 404 responses will still be considered as soft-stop. Make HTTP health checks consider response contents or specific status codes

May be used in sections :

defaults frontend listen backend

Arguments : is a keyword indicating how to look for a specific pattern in the response. The keyword may be one of "status", "rstatus", "string", or "rstring". The keyword may be preceded by an exclamation mark ("!") to negate the match. Spaces are allowed between the exclamation mark and the keyword. See below for more details on the supported keywords. is the pattern to look for. It may be a string or a regular expression. If the pattern contains spaces, they must be escaped with the usual backslash (''). By default, "option httpchk" considers that response statuses 2xx and 3xx are valid, and that others are invalid. When "http-check expect" is used, it defines what is considered valid or invalid. Only one "http-check" statement is supported in a backend. If a server fails to respond or times out, the check obviously fails. The available matches are : status : test the exact string match for the HTTP status code. A health check response will be considered valid if the response's status code is exactly this string. If the "status" keyword is prefixed with "!", then the response will be considered invalid if the status code matches. rstatus : test a regular expression for the HTTP status code. A health check response will be considered valid if the response's status code matches the expression. If the "rstatus" keyword is prefixed with "!", then the response will be considered invalid if the status code matches. This is mostly used to check for multiple codes. string : test the exact string match in the HTTP response body. A health check response will be considered valid if the response's body contains this exact string. If the "string" keyword is prefixed with "!", then the response will be considered invalid if the body contains this string. This can be used to look for a mandatory word at the end of a dynamic page, or to detect a failure when a specific error appears on the check page (eg: a stack trace). rstring : test a regular expression on the HTTP response body. A health check response will be considered valid if the response's body matches this expression. If the "rstring" keyword is prefixed with "!", then the response will be considered invalid if the body matches the expression. This can be used to look for a mandatory word at the end of a dynamic page, or to detect a failure when a specific error appears on the check page (eg: a stack trace). It is important to note that the responses will be limited to a certain size defined by the global "tune.chksize" option, which defaults to 16384 bytes. Thus, too large responses may not contain the mandatory pattern when using "string" or "rstring". If a large response is absolutely required, it is possible to change the default max size by setting the global variable. However, it is worth keeping in mind that parsing very large responses can waste some CPU cycles, especially when regular expressions are used, and that it is always better to focus the checks on smaller resources. Also "http-check expect" doesn't support HTTP keep-alive. Keep in mind that it will automatically append a "Connection: close" header, meaning that this header should not be present in the request provided by "option httpchk". Last, if "http-check expect" is combined with "http-check disable-on-404", then this last one has precedence when the server responds with 404. Examples : http-check expect status 200 http-check expect ! string SQL Error http-check expect ! rstatus ^5 http-check expect rstring <--><------------><----> | | | | `- trailing spaces ignored | | | `---------- value | | `-------------------- middle spaces ignored | `---------------------------- key `------------------------------------ leading spaces ignored Convert a string sample to upper case. This can only be placed after a string sample fetch function or after a transformation keyword returning a string type. The result is of type string.

7.3.2. Fetching samples from internal states

A first set of sample fetch methods applies to internal information which does not even relate to any client information. These ones are sometimes used with "monitor-fail" directives to report an internal status to external watchers. The sample fetch methods described in this section are usable anywhere. Always returns the boolean "false" value. It may be used with ACLs as a temporary replacement for another one when adjusting configurations. Always returns the boolean "true" value. It may be used with ACLs as a temporary replacement for another one when adjusting configurations. Returns the total number of queued connections of the designated backend divided by the number of active servers. The current backend is used if no backend is specified. This is very similar to "queue" except that the size of the farm is considered, in order to give a more accurate measurement of the time it may take for a new connection to be processed. The main usage is with ACL to return a sorry page to new users when it becomes certain they will get a degraded service, or to pass to the backend servers in a header so that they decide to work in degraded mode or to disable some functions to speed up the processing a bit. Note that in the event there would not be any active server anymore, twice the number of queued connections would be considered as the measured value. This is a fair estimate, as we expect one server to get back soon anyway, but we still prefer to send new traffic to another backend if in better shape. See also the "queue", "be_conn", and "be_sess_rate" sample fetches. Applies to the number of currently established connections on the backend, possibly including the connection being evaluated. If no backend name is specified, the current one is used. But it is also possible to check another backend. It can be used to use a specific farm when the nominal one is full. See also the "fe_conn", "queue" and "be_sess_rate" criteria. Returns an integer value corresponding to the sessions creation rate on the backend, in number of new sessions per second. This is used with ACLs to switch to an alternate backend when an expensive or fragile one reaches too high a session rate, or to limit abuse of service (eg. prevent sucking of an online dictionary). It can also be useful to add this element to logs using a log-format directive. Example : backend dynamic mode http acl being_scanned be_sess_rate gt 100 redirect location /denied.html if being_scanned Returns an integer value corresponding to the number of connection slots still available in the backend, by totaling the maximum amount of connections on all servers and the maximum queue size. This is probably only used with ACLs. The basic idea here is to be able to measure the number of connection "slots" still available (connection + queue), so that anything beyond that (intended usage; see "use_backend" keyword) can be redirected to a different backend. 'connslots' = number of available server connection slots, + number of available server queue slots. Note that while "fe_conn" may be used, "connslots" comes in especially useful when you have a case of traffic going to one single ip, splitting into multiple backends (perhaps using ACLs to do name-based load balancing) and you want to be able to differentiate between different backends, and their available "connslots". Also, whereas "nbsrv" only measures servers that are actually *down*, this fetch is more fine-grained and looks into the number of available connection slots as well. See also "queue" and "avg_queue". OTHER CAVEATS AND NOTES: at this point in time, the code does not take care of dynamic connections. Also, if any of the server maxconn, or maxqueue is 0, then this fetch clearly does not make sense, in which case the value returned will be -1. date([]) : integerReturns the current date as the epoch (number of seconds since 01/01/1970). If an offset value is specified, then it is a number of seconds that is added to the current date before returning the value. This is particularly useful to compute relative dates, as both positive and negative offsets are allowed. It is useful combined with the http_date converter. Example : http-response set-header Expires %[date(3600),http_date] Returns a string containing the value of environment variable . As a reminder, environment variables are per-process and are sampled when the process starts. This can be useful to pass some information to a next hop server, or with ACLs to take specific action when the process is started a certain way. Examples : http-request add-header Via 1.1 %[env(HOSTNAME)] http-request deny if !{ cook(SESSIONID) -m found } { env(STOP) -m found } Returns the number of currently established connections on the frontend, possibly including the connection being evaluated. If no frontend name is specified, the current one is used. But it is also possible to check another frontend. It can be used to return a sorry page before hard-blocking, or to use a specific backend to drain new requests when the farm is considered full. This is mostly used with ACLs but can also be used to pass some statistics to servers in HTTP headers. See also the "dst_conn", "be_conn", "fe_sess_rate" fetches. Returns an integer value corresponding to the sessions creation rate on the frontend, in number of new sessions per second. This is used with ACLs to limit the incoming session rate to an acceptable range in order to prevent abuse of service at the earliest moment, for example when combined with other layer 4 ACLs in order to force the clients to wait a bit for the rate to go down below the limit. It can also be useful to add this element to logs using a log-format directive. See also the "rate-limit sessions" directive for use in frontends. Example : frontend mail bind :25 mode tcp maxconn 100 acl too_fast fe_sess_rate ge 10 tcp-request inspect-delay 100ms tcp-request content accept if ! too_fast tcp-request content accept if WAIT_END Returns an integer value corresponding to the number of processes that were started (it equals the global "nbproc" setting). This is useful for logging and debugging purposes. nbsrv([]) : integerReturns an integer value corresponding to the number of usable servers of either the current backend or the named backend. This is mostly used with ACLs but can also be useful when added to logs. This is normally used to switch to an alternate backend when the number of servers is too low to to handle some load. It is useful to report a failure when combined with "monitor fail". Returns an integer value corresponding to the position of the process calling the function, between 1 and global.nbproc. This is useful for logging and debugging purposes. queue([]) : integerReturns the total number of queued connections of the designated backend, including all the connections in server queues. If no backend name is specified, the current one is used, but it is also possible to check another one. This is useful with ACLs or to pass statistics to backend servers. This can be used to take actions when queuing goes above a known level, generally indicating a surge of traffic or a massive slowdown on the servers. One possible action could be to reject new users but still accept old ones. See also the "avg_queue", "be_conn", and "be_sess_rate" fetches. rand([]) : integerReturns a random integer value within a range of possible values, starting at zero. If the range is not specified, it defaults to 2^32, which gives numbers between 0 and 4294967295. It can be useful to pass some values needed to take some routing decisions for example, or just for debugging purposes. This random must not be used for security purposes. srv_conn([/]) : integerReturns an integer value corresponding to the number of currently established connections on the designated server, possibly including the connection being evaluated. If is omitted, then the server is looked up in the current backend. It can be used to use a specific farm when one server is full, or to inform the server about our view of the number of active connections with it. See also the "fe_conn", "be_conn" and "queue" fetch methods. Returns true when the designated server is UP, and false when it is either DOWN or in maintenance mode. If is omitted, then the server is looked up in the current backend. It is mainly used to take action based on an external status reported via a health check (eg: a geographical site's availability). Another possible use which is more of a hack consists in using dummy servers as boolean variables that can be enabled or disabled from the CLI, so that rules depending on those ACLs can be tweaked in realtime. Returns an integer corresponding to the sessions creation rate on the designated server, in number of new sessions per second. If is omitted, then the server is looked up in the current backend. This is mostly used with ACLs but can make sense with logs too. This is used to switch to an alternate backend when an expensive or fragile one reaches too high a session rate, or to limit abuse of service (eg. prevent latent requests from overloading servers). Example : acl srv1_full srv_sess_rate(be1/srv1) gt 50 acl srv2_full srv_sess_rate(be1/srv2) gt 50 use_backend be2 if srv1_full or srv2_full Returns TRUE if the process calling the function is currently stopping. This can be useful for logging, or for relaxing certain checks or helping close certain connections upon graceful shutdown. Returns the total number of available entries in the current proxy's stick-table or in the designated stick-table. See also table_cnt. Returns the total number of entries currently in use in the current proxy's stick-table or in the designated stick-table. See also src_conn_cnt and table_avl for other entry counting methods.

7.3.3. Fetching samples at Layer 4

The layer 4 usually describes just the transport layer which in haproxy is closest to the connection, where no content is yet made available. The fetch methods described here are usable as low as the "tcp-request connection" rule sets unless they require some future information. Those generally include TCP/IP addresses and ports, as well as elements from stick-tables related to the incoming connection. For retrieving a value from a sticky counters, the counter number can be explicitly set as 0, 1, or 2 using the pre-defined "sc0_", "sc1_", or "sc2_" prefix, or it can be specified as the first integer argument when using the "sc_" prefix. An optional table may be specified with the "sc*" form, in which case the currently tracked key will be looked up into this alternate table instead of the table currently being tracked. Returns an integer containing the current backend's id. It can be used in frontends with responses to check which backend processed the request. This is the destination IPv4 address of the connection on the client side, which is the address the client connected to. It can be useful when running in transparent mode. It is of type IP and works on both IPv4 and IPv6 tables. On IPv6 tables, IPv4 address is mapped to its IPv6 equivalent, according to RFC 4291. Returns an integer value corresponding to the number of currently established connections on the same socket including the one being evaluated. It is normally used with ACLs but can as well be used to pass the information to servers in an HTTP header or in logs. It can be used to either return a sorry page before hard-blocking, or to use a specific backend to drain new requests when the socket is considered saturated. This offers the ability to assign different limits to different listening ports or addresses. See also the "fe_conn" and "be_conn" fetches. Returns an integer value corresponding to the destination TCP port of the connection on the client side, which is the port the client connected to. This might be used when running in transparent mode, when assigning dynamic ports to some clients for a whole application session, to stick all users to a same server, or to pass the destination port information to a server using an HTTP header. Returns an integer containing the current frontend's id. It can be used in backends to check from which backend it was called, or to stick all users coming via a same frontend to the same server. Returns the average client-to-server bytes rate from the currently tracked counters, measured in amount of bytes over the period configured in the table. See also src_bytes_in_rate. Returns the average server-to-client bytes rate from the currently tracked counters, measured in amount of bytes over the period configured in the table. See also src_bytes_out_rate. Clears the first General Purpose Counter associated to the currently tracked counters, and returns its previous value. Before the first invocation, the stored value is zero, so first invocation will always return zero. This is typically used as a second ACL in an expression in order to mark a connection when a first ACL was verified : # block if 5 consecutive requests continue to come faster than 10 sess # per second, and reset the counter as soon as the traffic slows down. acl abuse sc0_http_req_rate gt 10 acl kill sc0_inc_gpc0 gt 5 acl save sc0_clr_gpc0 ge 0 tcp-request connection accept if !abuse save tcp-request connection reject if abuse kill Returns the cumulated number of incoming connections from currently tracked counters. See also src_conn_cnt. Returns the current amount of concurrent connections tracking the same tracked counters. This number is automatically incremented when tracking begins and decremented when tracking stops. See also src_conn_cur. Returns the average connection rate from the currently tracked counters, measured in amount of connections over the period configured in the table. See also src_conn_rate. Returns the value of the first General Purpose Counter associated to the currently tracked counters. See also src_get_gpc0 and sc/sc0/sc1/sc2_inc_gpc0. Returns the average increment rate of the first General Purpose Counter associated to the currently tracked counters. It reports the frequency which the gpc0 counter was incremented over the configured period. See also src_gpc0_rate, sc/sc0/sc1/sc2_get_gpc0, and sc/sc0/sc1/sc2_inc_gpc0. Note that the "gpc0_rate" counter must be stored in the stick-table for a value to be returned, as "gpc0" only holds the event count. Returns the cumulated number of HTTP errors from the currently tracked counters. This includes the both request errors and 4xx error responses. See also src_http_err_cnt. Returns the average rate of HTTP errors from the currently tracked counters, measured in amount of errors over the period configured in the table. This includes the both request errors and 4xx error responses. See also src_http_err_rate. Returns the cumulated number of HTTP requests from the currently tracked counters. This includes every started request, valid or not. See also src_http_req_cnt. Returns the average rate of HTTP requests from the currently tracked counters, measured in amount of requests over the period configured in the table. This includes every started request, valid or not. See also src_http_req_rate. Increments the first General Purpose Counter associated to the currently tracked counters, and returns its new value. Before the first invocation, the stored value is zero, so first invocation will increase it to 1 and will return 1. This is typically used as a second ACL in an expression in order to mark a connection when a first ACL was verified : acl abuse sc0_http_req_rate gt 10 acl kill sc0_inc_gpc0 gt 0 tcp-request connection reject if abuse kill Returns the total amount of client-to-server data from the currently tracked counters, measured in kilobytes. The test is currently performed on 32-bit integers, which limits values to 4 terabytes. See also src_kbytes_in. Returns the total amount of server-to-client data from the currently tracked counters, measured in kilobytes. The test is currently performed on 32-bit integers, which limits values to 4 terabytes. See also src_kbytes_out. Returns the cumulated number of incoming connections that were transformed into sessions, which means that they were accepted by a "tcp-request connection" rule, from the currently tracked counters. A backend may count more sessions than connections because each connection could result in many backend sessions if some HTTP keep-alive is performed over the connection with the client. See also src_sess_cnt. Returns the average session rate from the currently tracked counters, measured in amount of sessions over the period configured in the table. A session is a connection that got past the early "tcp-request connection" rules. A backend may count more sessions than connections because each connection could result in many backend sessions if some HTTP keep-alive is performed over the connection with the client. See also src_sess_rate. Returns true if the designated session counter is currently being tracked by the current session. This can be useful when deciding whether or not we want to set some values in a header passed to the server. Returns the current amount of concurrent connections tracking the same tracked counters. This number is automatically incremented when tracking begins and decremented when tracking stops. It differs from sc0_conn_cur in that it does not rely on any stored information but on the table's reference count (the "use" value which is returned by "show table" on the CLI). This may sometimes be more suited for layer7 tracking. It can be used to tell a server how many concurrent connections there are from a given address for example. Returns an integer containing the current listening socket's id. It is useful in frontends involving many "bind" lines, or to stick all users coming via a same socket to the same server. This is the source IPv4 address of the client of the session. It is of type IP and works on both IPv4 and IPv6 tables. On IPv6 tables, IPv4 addresses are mapped to their IPv6 equivalent, according to RFC 4291. Note that it is the TCP-level source address which is used, and not the address of a client behind a proxy. However if the "accept-proxy" bind directive is used, it can be the address of a client behind another PROXY-protocol compatible component for all rule sets except "tcp-request connection" which sees the real address. Example: http-request set-header X-Country %[src,map_ip(geoip.lst)] Returns the average bytes rate from the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, measured in amount of bytes over the period configured in the table. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_bytes_in_rate. Returns the average bytes rate to the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, measured in amount of bytes over the period configured in the table. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_bytes_out_rate. Clears the first General Purpose Counter associated to the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, and returns its previous value. If the address is not found, an entry is created and 0 is returned. This is typically used as a second ACL in an expression in order to mark a connection when a first ACL was verified : # block if 5 consecutive requests continue to come faster than 10 sess # per second, and reset the counter as soon as the traffic slows down. acl abuse src_http_req_rate gt 10 acl kill src_inc_gpc0 gt 5 acl save src_clr_gpc0 ge 0 tcp-request connection accept if !abuse save tcp-request connection reject if abuse kill Returns the cumulated number of connections initiated from the current incoming connection's source address in the current proxy's stick-table or in the designated stick-table. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_conn_cnt. Returns the current amount of concurrent connections initiated from the current incoming connection's source address in the current proxy's stick-table or in the designated stick-table. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_conn_cur. Returns the average connection rate from the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, measured in amount of connections over the period configured in the table. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_conn_rate. Returns the value of the first General Purpose Counter associated to the incoming connection's source address in the current proxy's stick-table or in the designated stick-table. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_get_gpc0 and src_inc_gpc0. Returns the average increment rate of the first General Purpose Counter associated to the incoming connection's source address in the current proxy's stick-table or in the designated stick-table. It reports the frequency which the gpc0 counter was incremented over the configured period. See also sc/sc0/sc1/sc2_gpc0_rate, src_get_gpc0, and sc/sc0/sc1/sc2_inc_gpc0. Note that the "gpc0_rate" counter must be stored in the stick-table for a value to be returned, as "gpc0" only holds the event count. Returns the cumulated number of HTTP errors from the incoming connection's source address in the current proxy's stick-table or in the designated stick-table. This includes the both request errors and 4xx error responses. See also sc/sc0/sc1/sc2_http_err_cnt. If the address is not found, zero is returned. Returns the average rate of HTTP errors from the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, measured in amount of errors over the period configured in the table. This includes the both request errors and 4xx error responses. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_http_err_rate. Returns the cumulated number of HTTP requests from the incoming connection's source address in the current proxy's stick-table or in the designated stick- table. This includes every started request, valid or not. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_http_req_cnt. Returns the average rate of HTTP requests from the incoming connection's source address in the current proxy's stick-table or in the designated stick- table, measured in amount of requests over the period configured in the table. This includes every started request, valid or not. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_http_req_rate. Increments the first General Purpose Counter associated to the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, and returns its new value. If the address is not found, an entry is created and 1 is returned. See also sc0/sc2/sc2_inc_gpc0. This is typically used as a second ACL in an expression in order to mark a connection when a first ACL was verified : acl abuse src_http_req_rate gt 10 acl kill src_inc_gpc0 gt 0 tcp-request connection reject if abuse kill Returns the total amount of data received from the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, measured in kilobytes. If the address is not found, zero is returned. The test is currently performed on 32-bit integers, which limits values to 4 terabytes. See also sc/sc0/sc1/sc2_kbytes_in. Returns the total amount of data sent to the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, measured in kilobytes. If the address is not found, zero is returned. The test is currently performed on 32-bit integers, which limits values to 4 terabytes. See also sc/sc0/sc1/sc2_kbytes_out. Returns an integer value corresponding to the TCP source port of the connection on the client side, which is the port the client connected from. Usage of this function is very limited as modern protocols do not care much about source ports nowadays. Returns the cumulated number of connections initiated from the incoming connection's source IPv4 address in the current proxy's stick-table or in the designated stick-table, that were transformed into sessions, which means that they were accepted by "tcp-request" rules. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_sess_cnt. Returns the average session rate from the incoming connection's source address in the current proxy's stick-table or in the designated stick-table, measured in amount of sessions over the period configured in the table. A session is a connection that went past the early "tcp-request" rules. If the address is not found, zero is returned. See also sc/sc0/sc1/sc2_sess_rate. Creates or updates the entry associated to the incoming connection's source address in the current proxy's stick-table or in the designated stick-table. This table must be configured to store the "conn_cnt" data type, otherwise the match will be ignored. The current count is incremented by one, and the expiration timer refreshed. The updated count is returned, so this match can't return zero. This was used to reject service abusers based on their source address. Note: it is recommended to use the more complete "track-sc*" actions in "tcp-request" rules instead. Example : listen ssh bind :22 mode tcp maxconn 100 stick-table type ip size 20 expire 10s store conn_cnt tcp-request content reject if { src_updt_conn_cnt gt 3 } server local 127.0.0.1:22 Returns an integer containing the server's id when processing the response. While it's almost only used with ACLs, it may be used for logging or debugging.

7.3.4. Fetching samples at Layer 5

The layer 5 usually describes just the session layer which in haproxy is closest to the session once all the connection handshakes are finished, but when no content is yet made available. The fetch methods described here are usable as low as the "tcp-request content" rule sets unless they require some future information. Those generally include the results of SSL negotiations. Returns true when the back connection was made via an SSL/TLS transport layer and is locally deciphered. This means the outgoing connection was made other a server with the "ssl" option. Returns the symmetric cipher key size supported in bits when the outgoing connection was made over an SSL/TLS transport layer. Returns the name of the used cipher when the outgoing connection was made over an SSL/TLS transport layer. Returns the name of the used protocol when the outgoing connection was made over an SSL/TLS transport layer. When the outgoing connection was made over an SSL/TLS transport layer, returns the TLS unique ID as defined in RFC5929 section 3. The unique id can be encoded to base64 using the converter: "ssl_bc_unique_id,base64". Returns the SSL ID of the back connection when the outgoing connection was made over an SSL/TLS transport layer. It is useful to log if we want to know if session was reused or not. Returns the symmetric cipher key size used in bits when the outgoing connection was made over an SSL/TLS transport layer. When the incoming connection was made over an SSL/TLS transport layer, returns the ID of the first error detected during verification of the client certificate at depth > 0, or 0 if no error was encountered during this verification process. Please refer to your SSL library's documentation to find the exhaustive list of error codes. When the incoming connection was made over an SSL/TLS transport layer, returns the depth in the CA chain of the first error detected during the verification of the client certificate. If no error is encountered, 0 is returned. Returns the DER formatted certificate presented by the client when the incoming connection was made over an SSL/TLS transport layer. When used for an ACL, the value(s) to match against can be passed in hexadecimal form. When the incoming connection was made over an SSL/TLS transport layer, returns the ID of the first error detected during verification at depth 0, or 0 if no error was encountered during this verification process. Please refer to your SSL library's documentation to find the exhaustive list of error codes. When the incoming connection was made over an SSL/TLS transport layer, returns the full distinguished name of the issuer of the certificate presented by the client when no is specified, or the value of the first given entry found from the beginning of the DN. If a positive/negative occurrence number is specified as the optional second argument, it returns the value of the nth given entry value from the beginning/end of the DN. For instance, "ssl_c_i_dn(OU,2)" the second organization unit, and "ssl_c_i_dn(CN)" retrieves the common name. Returns the name of the algorithm used to generate the key of the certificate presented by the client when the incoming connection was made over an SSL/TLS transport layer. Returns the end date presented by the client as a formatted string YYMMDDhhmmss[Z] when the incoming connection was made over an SSL/TLS transport layer. Returns the start date presented by the client as a formatted string YYMMDDhhmmss[Z] when the incoming connection was made over an SSL/TLS transport layer. When the incoming connection was made over an SSL/TLS transport layer, returns the full distinguished name of the subject of the certificate presented by the client when no is specified, or the value of the first given entry found from the beginning of the DN. If a positive/negative occurrence number is specified as the optional second argument, it returns the value of the nth given entry value from the beginning/end of the DN. For instance, "ssl_c_s_dn(OU,2)" the second organization unit, and "ssl_c_s_dn(CN)" retrieves the common name. Returns the serial of the certificate presented by the client when the incoming connection was made over an SSL/TLS transport layer. When used for an ACL, the value(s) to match against can be passed in hexadecimal form. Returns the SHA-1 fingerprint of the certificate presented by the client when the incoming connection was made over an SSL/TLS transport layer. This can be used to stick a client to a server, or to pass this information to a server. Note that the output is binary, so if you want to pass that signature to the server, you need to encode it in hex or base64, such as in the example below: http-request set-header X-SSL-Client-SHA1 %[ssl_c_sha1,hex] Returns the name of the algorithm used to sign the certificate presented by the client when the incoming connection was made over an SSL/TLS transport layer. Returns true if current SSL session uses a client certificate even if current connection uses SSL session resumption. See also "ssl_fc_has_crt". Returns the verify result error ID when the incoming connection was made over an SSL/TLS transport layer, otherwise zero if no error is encountered. Please refer to your SSL library's documentation for an exhaustive list of error codes. Returns the version of the certificate presented by the client when the incoming connection was made over an SSL/TLS transport layer. Returns the DER formatted certificate presented by the frontend when the incoming connection was made over an SSL/TLS transport layer. When used for an ACL, the value(s) to match against can be passed in hexadecimal form. When the incoming connection was made over an SSL/TLS transport layer, returns the full distinguished name of the issuer of the certificate presented by the frontend when no is specified, or the value of the first given entry found from the beginning of the DN. If a positive/negative occurrence number is specified as the optional second argument, it returns the value of the nth given entry value from the beginning/end of the DN. For instance, "ssl_f_i_dn(OU,2)" the second organization unit, and "ssl_f_i_dn(CN)" retrieves the common name. Returns the name of the algorithm used to generate the key of the certificate presented by the frontend when the incoming connection was made over an SSL/TLS transport layer. Returns the end date presented by the frontend as a formatted string YYMMDDhhmmss[Z] when the incoming connection was made over an SSL/TLS transport layer. Returns the start date presented by the frontend as a formatted string YYMMDDhhmmss[Z] when the incoming connection was made over an SSL/TLS transport layer. When the incoming connection was made over an SSL/TLS transport layer, returns the full distinguished name of the subject of the certificate presented by the frontend when no is specified, or the value of the first given entry found from the beginning of the DN. If a positive/negative occurrence number is specified as the optional second argument, it returns the value of the nth given entry value from the beginning/end of the DN. For instance, "ssl_f_s_dn(OU,2)" the second organization unit, and "ssl_f_s_dn(CN)" retrieves the common name. Returns the serial of the certificate presented by the frontend when the incoming connection was made over an SSL/TLS transport layer. When used for an ACL, the value(s) to match against can be passed in hexadecimal form. Returns the SHA-1 fingerprint of the certificate presented by the frontend when the incoming connection was made over an SSL/TLS transport layer. This can be used to know which certificate was chosen using SNI. Returns the name of the algorithm used to sign the certificate presented by the frontend when the incoming connection was made over an SSL/TLS transport layer. Returns the version of the certificate presented by the frontend when the incoming connection was made over an SSL/TLS transport layer. Returns true when the front connection was made via an SSL/TLS transport layer and is locally deciphered. This means it has matched a socket declared with a "bind" line having the "ssl" option. Example : listen http-https bind :80 bind :443 ssl crt /etc/haproxy.pem http-request add-header X-Proto https if { ssl_fc } Returns the symmetric cipher key size supported in bits when the incoming connection was made over an SSL/TLS transport layer. This extracts the Application Layer Protocol Negotiation field from an incoming connection made via a TLS transport layer and locally deciphered by haproxy. The result is a string containing the protocol name advertised by the client. The SSL library must have been built with support for TLS extensions enabled (check haproxy -vv). Note that the TLS ALPN extension is not advertised unless the "alpn" keyword on the "bind" line specifies a protocol list. Also, nothing forces the client to pick a protocol from this list, any other one may be requested. The TLS ALPN extension is meant to replace the TLS NPN extension. See also "ssl_fc_npn". Returns the name of the used cipher when the incoming connection was made over an SSL/TLS transport layer. Returns true if a client certificate is present in an incoming connection over SSL/TLS transport layer. Useful if 'verify' statement is set to 'optional'. Note: on SSL session resumption with Session ID or TLS ticket, client certificate is not present in the current connection but may be retrieved from the cache or the ticket. So prefer "ssl_c_used" if you want to check if current SSL session uses a client certificate. This checks for the presence of a Server Name Indication TLS extension (SNI) in an incoming connection was made over an SSL/TLS transport layer. Returns true when the incoming connection presents a TLS SNI field. This requires that the SSL library is build with support for TLS extensions enabled (check haproxy -vv). This extracts the Next Protocol Negotiation field from an incoming connection made via a TLS transport layer and locally deciphered by haproxy. The result is a string containing the protocol name advertised by the client. The SSL library must have been built with support for TLS extensions enabled (check haproxy -vv). Note that the TLS NPN extension is not advertised unless the "npn" keyword on the "bind" line specifies a protocol list. Also, nothing forces the client to pick a protocol from this list, any other one may be requested. Please note that the TLS NPN extension was replaced with ALPN. Returns the name of the used protocol when the incoming connection was made over an SSL/TLS transport layer. When the incoming connection was made over an SSL/TLS transport layer, returns the TLS unique ID as defined in RFC5929 section 3. The unique id can be encoded to base64 using the converter: "ssl_bc_unique_id,base64". Returns the SSL ID of the front connection when the incoming connection was made over an SSL/TLS transport layer. It is useful to stick a given client to a server. It is important to note that some browsers refresh their session ID every few minutes. This extracts the Server Name Indication TLS extension (SNI) field from an incoming connection made via an SSL/TLS transport layer and locally deciphered by haproxy. The result (when present) typically is a string matching the HTTPS host name (253 chars or less). The SSL library must have been built with support for TLS extensions enabled (check haproxy -vv). This fetch is different from "req_ssl_sni" above in that it applies to the connection being deciphered by haproxy and not to SSL contents being blindly forwarded. See also "ssl_fc_sni_end" and "ssl_fc_sni_reg" below. This requires that the SSL library is build with support for TLS extensions enabled (check haproxy -vv). ACL derivatives : ssl_fc_sni_end : suffix match ssl_fc_sni_reg : regex match Returns the symmetric cipher key size used in bits when the incoming connection was made over an SSL/TLS transport layer.

7.3.5. Fetching samples from buffer contents (Layer 6)

Fetching samples from buffer contents is a bit different from the previous sample fetches above because the sampled data are ephemeral. These data can only be used when they're available and will be lost when they're forwarded. For this reason, samples fetched from buffer contents during a request cannot be used in a response for example. Even while the data are being fetched, they can change. Sometimes it is necessary to set some delays or combine multiple sample fetch methods to ensure that the expected data are complete and usable, for example through TCP request content inspection. Please see the "tcp-request content" keyword for more detailed information on the subject. payload(,) : binary (deprecated)This is an alias for "req.payload" when used in the context of a request (eg: "stick on", "stick match"), and for "res.payload" when used in the context of a response such as in "stick store response". payload_lv(,[,]) : binary (deprecated)This is an alias for "req.payload_lv" when used in the context of a request (eg: "stick on", "stick match"), and for "res.payload_lv" when used in the context of a response such as in "stick store response". Returns an integer value corresponding to the number of bytes present in the request buffer. This is mostly used in ACL. It is important to understand that this test does not return false as long as the buffer is changing. This means that a check with equality to zero will almost always immediately match at the beginning of the session, while a test for more data will wait for that data to come in and return false only when haproxy is certain that no more data will come in. This test was designed to be used with TCP request content inspection. This extracts a binary block of bytes and starting at byte in the request buffer. As a special case, if the argument is zero, the the whole buffer from to the end is extracted. This can be used with ACLs in order to check for the presence of some content in a buffer at any location. ACL alternatives : payload(,) : hex binary match This extracts a binary block whose size is specified at for bytes, and which starts at if specified or just after the length in the request buffer. The parameter also supports relative offsets if prepended with a '+' or '-' sign. ACL alternatives : payload_lv(,[,]) : hex binary match Returns true when data in the request buffer look like HTTP and correctly parses as such. It is the same parser as the common HTTP request parser which is used so there should be no surprises. The test does not match until the request is complete, failed or timed out. This test may be used to report the protocol in TCP logs, but the biggest use is to block TCP request analysis until a complete HTTP request is present in the buffer, for example to track a header. Example: tcp-request inspect-delay 10s tcp-request content reject if !HTTP tcp-request content track-sc0 base table req-rate When the request buffer looks like the RDP protocol, extracts the RDP cookie , or any cookie if unspecified. The parser only checks for the first cookie, as illustrated in the RDP protocol specification. The cookie name is case insensitive. Generally the "MSTS" cookie name will be used, as it can contain the user name of the client connecting to the server if properly configured on the client. The "MSTSHASH" cookie is often used as well for session stickiness to servers. This differs from "balance rdp-cookie" in that any balancing algorithm may be used and thus the distribution of clients to backend servers is not linked to a hash of the RDP cookie. It is envisaged that using a balancing algorithm such as "balance roundrobin" or "balance leastconn" will lead to a more even distribution of clients to backend servers than the hash used by "balance rdp-cookie". ACL derivatives : req_rdp_cookie([]) : exact string match Example : listen tse-farm bind 0.0.0.0:3389 tcp-request inspect-delay 5s tcp-request content accept if RDP_COOKIE persist rdp-cookie stick-table type string size 204800 stick on req.rdp_cookie(mstshash) server srv1 1.1.1.1:3389 server srv1 1.1.1.2:3389 Tries to parse the request buffer as RDP protocol, then returns an integer corresponding to the number of RDP cookies found. If an optional cookie name is passed, only cookies matching this name are considered. This is mostly used in ACL. ACL derivatives : req_rdp_cookie_cnt([]) : integer match Returns an integer value containing the type of the SSL hello message found in the request buffer if the buffer contains data that parse as a complete SSL (v3 or superior) client hello message. Note that this only applies to raw contents found in the request buffer and not to contents deciphered via an SSL data layer, so this will not work with "bind" lines having the "ssl" option. This is mostly used in ACL to detect presence of an SSL hello message that is supposed to contain an SSL session ID usable for stickiness. Returns a string containing the value of the Server Name TLS extension sent by a client in a TLS stream passing through the request buffer if the buffer contains data that parse as a complete SSL (v3 or superior) client hello message. Note that this only applies to raw contents found in the request buffer and not to contents deciphered via an SSL data layer, so this will not work with "bind" lines having the "ssl" option. SNI normally contains the name of the host the client tries to connect to (for recent browsers). SNI is useful for allowing or denying access to certain hosts when SSL/TLS is used by the client. This test was designed to be used with TCP request content inspection. If content switching is needed, it is recommended to first wait for a complete client hello (type 1), like in the example below. See also "ssl_fc_sni". ACL derivatives : req_ssl_sni : exact string match Examples : tcp-request inspect-delay 5s tcp-request content accept if { req_ssl_hello_type 1 } use_backend bk_allow if { req_ssl_sni -f allowed_sites } default_backend bk_sorry_page Returns an integer value containing the type of the SSL hello message found in the response buffer if the buffer contains data that parses as a complete SSL (v3 or superior) hello message. Note that this only applies to raw contents found in the response buffer and not to contents deciphered via an SSL data layer, so this will not work with "server" lines having the "ssl" option. This is mostly used in ACL to detect presence of an SSL hello message that is supposed to contain an SSL session ID usable for stickiness. Returns an integer value containing the version of the SSL/TLS protocol of a stream present in the request buffer. Both SSLv2 hello messages and SSLv3 messages are supported. TLSv1 is announced as SSL version 3.1. The value is composed of the major version multiplied by 65536, added to the minor version. Note that this only applies to raw contents found in the request buffer and not to contents deciphered via an SSL data layer, so this will not work with "bind" lines having the "ssl" option. The ACL version of the test matches against a decimal notation in the form MAJOR.MINOR (eg: 3.1). This fetch is mostly used in ACL. ACL derivatives : req_ssl_ver : decimal match Returns an integer value corresponding to the number of bytes present in the response buffer. This is mostly used in ACL. It is important to understand that this test does not return false as long as the buffer is changing. This means that a check with equality to zero will almost always immediately match at the beginning of the session, while a test for more data will wait for that data to come in and return false only when haproxy is certain that no more data will come in. This test was designed to be used with TCP response content inspection. This extracts a binary block of bytes and starting at byte in the response buffer. As a special case, if the argument is zero, the the whole buffer from to the end is extracted. This can be used with ACLs in order to check for the presence of some content in a buffer at any location. This extracts a binary block whose size is specified at for bytes, and which starts at if specified or just after the length in the response buffer. The parameter also supports relative offsets if prepended with a '+' or '-' sign. This fetch either returns true when the inspection period is over, or does not fetch. It is only used in ACLs, in conjunction with content analysis to avoid returning a wrong verdict early. It may also be used to delay some actions, such as a delayed reject for some special addresses. Since it either stops the rules evaluation or immediately returns true, it is recommended to use this acl as the last one in a rule. Please note that the default ACL "WAIT_END" is always usable without prior declaration. This test was designed to be used with TCP request content inspection. Examples : tcp-request inspect-delay 2s tcp-request content accept if WAIT_END tcp-request inspect-delay 10s acl goodguys src 10.0.0.0/24 acl badguys src 10.0.1.0/24 tcp-request content accept if goodguys tcp-request content reject if badguys WAIT_END tcp-request content reject

7.3.6. Fetching HTTP samples (Layer 7)

It is possible to fetch samples from HTTP contents, requests and responses. This application layer is also called layer 7. It is only possible to fetch the data in this section when a full HTTP request or response has been parsed from its respective request or response buffer. This is always the case with all HTTP specific rules and for sections running with "mode http". When using TCP content inspection, it may be necessary to support an inspection delay in order to let the request or response come in first. These fetches may require a bit more CPU resources than the layer 4 ones, but not much since the request and response are indexed. This returns the concatenation of the first Host header and the path part of the request, which starts at the first slash and ends before the question mark. It can be useful in virtual hosted environments to detect URL abuses as well as to improve shared caches efficiency. Using this with a limited size stick table also allows one to collect statistics about most commonly requested objects by host/path. With ACLs it can allow simple content switching rules involving the host and the path at the same time, such as "www.example.com/favicon.ico". See also "path" and "uri". ACL derivatives : base : exact string match base_beg : prefix match base_dir : subdir match base_dom : domain match base_end : suffix match base_len : length match base_reg : regex match base_sub : substring match This returns a 32-bit hash of the value returned by the "base" fetch method above. This is useful to track per-URL activity on high traffic sites without having to store all URLs. Instead a shorter hash is stored, saving a lot of memory. The output type is an unsigned integer. This returns the concatenation of the base32 fetch above and the src fetch below. The resulting type is of type binary, with a size of 8 or 20 bytes depending on the source address family. This can be used to track per-IP, per-URL counters. This extracts the content of the header captured by the "capture request header", idx is the position of the capture keyword in the configuration. This extracts the METHOD of an HTTP request. It can be used in both request and response. Unlike "method", it can be used in both request and response because it's allocated. This extracts the request's URI, which starts at the first slash and ends before the first space in the request (without the host part). Unlike "path" and "url", it can be used in both request and response because it's allocated. This extracts the request's HTTP version and returns either "HTTP/1.0" or "HTTP/1.1". Unlike "req.ver", it can be used in both request, response, and logs because it relies on a persistent flag. This extracts the content of the header captured by the "capture response header", idx is the position of the capture keyword in the configuration. The first entry is an index of 0. This extracts the response's HTTP version and returns either "HTTP/1.0" or "HTTP/1.1". Unlike "res.ver", it can be used in logs because it relies on a persistent flag. cook([]) : string (deprecated)This extracts the last occurrence of the cookie name on a "Cookie" header line from the request, and returns its value as string. If no name is specified, the first cookie value is returned. When used with ACLs, all matching cookies are evaluated. Spaces around the name and the value are ignored as requested by the Cookie header specification (RFC6265). The cookie name is case-sensitive. Empty cookies are valid, so an empty cookie may very well return an empty value if it is present. Use the "found" match to detect presence. Use the res.cook() variant for response cookies sent by the server. ACL derivatives : cook([]) : exact string match cook_beg([]) : prefix match cook_dir([]) : subdir match cook_dom([]) : domain match cook_end([]) : suffix match cook_len([]) : length match cook_reg([]) : regex match cook_sub([]) : substring match cook_cnt([]) : integer (deprecated)Returns an integer value representing the number of occurrences of the cookie in the request, or all cookies if is not specified. cook_val([]) : integer (deprecated)This extracts the last occurrence of the cookie name on a "Cookie" header line from the request, and converts its value to an integer which is returned. If no name is specified, the first cookie value is returned. When used in ACLs, all matching names are iterated over until a value matches. cookie([]) : string (deprecated)This extracts the last occurrence of the cookie name on a "Cookie" header line from the request, or a "Set-Cookie" header from the response, and returns its value as a string. A typical use is to get multiple clients sharing a same profile use the same server. This can be similar to what "appsession" does with the "request-learn" statement, but with support for multi-peer synchronization and state keeping across restarts. If no name is specified, the first cookie value is returned. This fetch should not be used anymore and should be replaced by req.cook() or res.cook() instead as it ambiguously uses the direction based on the context where it is used. hdr([[,]]) : stringThis is equivalent to req.hdr() when used on requests, and to res.hdr() when used on responses. Please refer to these respective fetches for more details. In case of doubt about the fetch direction, please use the explicit ones. Note that contrary to the hdr() sample fetch method, the hdr_* ACL keywords unambiguously apply to the request headers. This extracts the last occurrence of header in an HTTP request. When used from an ACL, all occurrences are iterated over until a match is found. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. It differs from req.hdr() in that any commas present in the value are returned and are not used as delimiters. This is sometimes useful with headers such as User-Agent. Returns an integer value representing the number of occurrences of request header field name , or the total number of header fields if is not specified. Contrary to its req.hdr_cnt() cousin, this function returns the number of full line headers and does not stop on commas. This extracts the last occurrence of header in an HTTP request. When used from an ACL, all occurrences are iterated over until a match is found. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. A typical use is with the X-Forwarded-For header once converted to IP, associated with an IP stick-table. The function considers any comma as a delimiter for distinct values. If full-line headers are desired instead, use req.fhdr(). Please carefully check RFC2616 to know how certain headers are supposed to be parsed. Also, some of them are case insensitive (eg: Connection). ACL derivatives : hdr([[,]]) : exact string match hdr_beg([[,]]) : prefix match hdr_dir([[,]]) : subdir match hdr_dom([[,]]) : domain match hdr_end([[,]]) : suffix match hdr_len([[,]]) : length match hdr_reg([[,]]) : regex match hdr_sub([[,]]) : substring match hdr_cnt([

]) : integer (deprecated)Returns an integer value representing the number of occurrences of request header field name , or the total number of header field values if is not specified. It is important to remember that one header line may count as several headers if it has several values. The function considers any comma as a delimiter for distinct values. If full-line headers are desired instead, req.fhdr_cnt() should be used instead. With ACLs, it can be used to detect presence, absence or abuse of a specific header, as well as to block request smuggling attacks by rejecting requests which contain more than one of certain headers. See "req.hdr" for more information on header matching. hdr_ip([[,]]) : ip (deprecated)This extracts the last occurrence of header in an HTTP request, converts it to an IPv4 or IPv6 address and returns this address. When used with ACLs, all occurrences are checked, and if is omitted, every value of every header is checked. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. A typical use is with the X-Forwarded-For and X-Client-IP headers. hdr_val([[,]]) : integer (deprecated)This extracts the last occurrence of header in an HTTP request, and converts it to an integer value. When used with ACLs, all occurrences are checked, and if is omitted, every value of every header is checked. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. A typical use is with the X-Forwarded-For header. Returns a boolean indicating whether the authentication data received from the client match a username & password stored in the specified userlist. This fetch function is not really useful outside of ACLs. Currently only http basic auth is supported. Returns a string corresponding to the user name found in the authentication data received from the client if both the user name and password are valid according to the specified userlist. The main purpose is to use it in ACLs where it is then checked whether the user belongs to any group within a list. This fetch function is not really useful outside of ACLs. Currently only http basic auth is supported. ACL derivatives : http_auth_group() : group ... Returns true when the user extracted from the request and whose password is valid according to the specified userlist belongs to at least one of the groups. Returns true when the request being processed is the first one of the connection. This can be used to add or remove headers that may be missing from some requests when a request is not the first one, or to help grouping requests in the logs. Returns an integer value corresponding to the method in the HTTP request. For example, "GET" equals 1 (check sources to establish the matching). Value 9 means "other method" and may be converted to a string extracted from the stream. This should not be used directly as a sample, this is only meant to be used from ACLs, which transparently convert methods from patterns to these integer + string values. Some predefined ACL already check for most common methods. ACL derivatives : method : case insensitive method match Example : acl valid_method method GET HEAD http-request deny if ! valid_method This extracts the request's URL path, which starts at the first slash and ends before the question mark (without the host part). A typical use is with prefetch-capable caches, and with portals which need to aggregate multiple information from databases and keep them in caches. Note that with outgoing caches, it would be wiser to use "url" instead. With ACLs, it's typically used to match exact file names (eg: "/login.php"), or directory parts using the derivative forms. See also the "url" and "base" fetch methods. ACL derivatives : path : exact string match path_beg : prefix match path_dir : subdir match path_dom : domain match path_end : suffix match path_len : length match path_reg : regex match path_sub : substring match Returns the version string from the HTTP request, for example "1.1". This can be useful for logs, but is mostly there for ACL. Some predefined ACL already check for versions 1.0 and 1.1. ACL derivatives : req_ver : exact string match Returns the boolean "true" value if the response has been compressed by HAProxy, otherwise returns boolean "false". This may be used to add information in the logs. Returns a string containing the name of the algorithm used if the response was compressed by HAProxy, for example : "deflate". This may be used to add some information in the logs. scook([]) : string (deprecated)This extracts the last occurrence of the cookie name on a "Set-Cookie" header line from the response, and returns its value as string. If no name is specified, the first cookie value is returned. ACL derivatives : scook([] : exact string match Returns an integer value representing the number of occurrences of the cookie in the response, or all cookies if is not specified. This is mostly useful when combined with ACLs to detect suspicious responses. This extracts the last occurrence of the cookie name on a "Set-Cookie" header line from the response, and converts its value to an integer which is returned. If no name is specified, the first cookie value is returned. This extracts the last occurrence of header in an HTTP response, or of the last header if no is specified. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. It differs from res.hdr() in that any commas present in the value are returned and are not used as delimiters. If this is not desired, the res.hdr() fetch should be used instead. This is sometimes useful with headers such as Date or Expires. Returns an integer value representing the number of occurrences of response header field name , or the total number of header fields if is not specified. Contrary to its res.hdr_cnt() cousin, this function returns the number of full line headers and does not stop on commas. If this is not desired, the res.hdr_cnt() fetch should be used instead. shdr([[,]]) : string (deprecated)This extracts the last occurrence of header in an HTTP response, or of the last header if no is specified. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. This can be useful to learn some data into a stick-table. The function considers any comma as a delimiter for distinct values. If this is not desired, the res.fhdr() fetch should be used instead. ACL derivatives : shdr([[,]]) : exact string match shdr_beg([[,]]) : prefix match shdr_dir([[,]]) : subdir match shdr_dom([[,]]) : domain match shdr_end([[,]]) : suffix match shdr_len([[,]]) : length match shdr_reg([[,]]) : regex match shdr_sub([[,]]) : substring match shdr_cnt([]) : integer (deprecated)Returns an integer value representing the number of occurrences of response header field name , or the total number of header fields if is not specified. The function considers any comma as a delimiter for distinct values. If this is not desired, the res.fhdr_cnt() fetch should be used instead. shdr_ip([[,]]) : ip (deprecated)This extracts the last occurrence of header in an HTTP response, convert it to an IPv4 or IPv6 address and returns this address. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. This can be useful to learn some data into a stick table. shdr_val([[,]]) : integer (deprecated)This extracts the last occurrence of header in an HTTP response, and converts it to an integer value. Optionally, a specific occurrence might be specified as a position number. Positive values indicate a position from the first occurrence, with 1 being the first one. Negative values indicate positions relative to the last one, with -1 being the last one. This can be useful to learn some data into a stick table. Returns the version string from the HTTP response, for example "1.1". This can be useful for logs, but is mostly there for ACL. ACL derivatives : resp_ver : exact string match This extracts the last occurrence of the cookie name on a "Set-Cookie" header line from the response and uses the corresponding value to match. This can be comparable to what "appsession" does with default options, but with support for multi-peer synchronization and state keeping across restarts. This fetch function is deprecated and has been superseded by the "res.cook" fetch. This keyword will disappear soon. Returns an integer containing the HTTP status code in the HTTP response, for example, 302. It is mostly used within ACLs and integer ranges, for example, to remove any Location header if the response is not a 3xx. This extracts the request's URL as presented in the request. A typical use is with prefetch-capable caches, and with portals which need to aggregate multiple information from databases and keep them in caches. With ACLs, using "path" is preferred over using "url", because clients may send a full URL as is normally done with proxies. The only real use is to match "*" which does not match in "path", and for which there is already a predefined ACL. See also "path" and "base". ACL derivatives : url : exact string match url_beg : prefix match url_dir : subdir match url_dom : domain match url_end : suffix match url_len : length match url_reg : regex match url_sub : substring match This extracts the IP address from the request's URL when the host part is presented as an IP address. Its use is very limited. For instance, a monitoring system might use this field as an alternative for the source IP in order to test what path a given source address would follow, or to force an entry in a table for a given source address. With ACLs it can be used to restrict access to certain systems through a proxy, for example when combined with option "http_proxy". This extracts the port part from the request's URL. Note that if the port is not specified in the request, port 80 is assumed. With ACLs it can be used to restrict access to certain systems through a proxy, for example when combined with option "http_proxy". urlp([,]) : stringThis extracts the first occurrence of the parameter in the query string, which begins after either '?' or , and which ends before '&', ';' or . The parameter name is case-sensitive. The result is a string corresponding to the value of the parameter as presented in the request (no URL decoding is performed). This can be used for session stickiness based on a client ID, to extract an application cookie passed as a URL parameter, or in ACLs to apply some checks. Note that the ACL version of this fetch do not iterate over multiple parameters and stop at the first one as well. ACL derivatives : urlp([,]) : exact string match urlp_beg([,]) : prefix match urlp_dir([,]) : subdir match urlp_dom([,]) : domain match urlp_end([,]) : suffix match urlp_len([,]) : length match urlp_reg([,]) : regex match urlp_sub([,]) : substring match Example : stick on urlp(PHPSESSIONID) stick on urlp(JSESSIONID,;) See "urlp" above. This one extracts the URL parameter in the request and converts it to an integer value. This can be used for session stickiness based on a user ID for example, or with ACLs to match a page number or price.

7.4. Pre-defined ACLs

Some predefined ACLs are hard-coded so that they do not have to be declared in every frontend which needs them. They all have their names in upper case in order to avoid confusion. Their equivalence is provided below.

ACL name Equivalent to Usage
FALSE always_false never match
HTTP req_proto_http match if protocol is valid HTTP
HTTP_1.0 req_ver 1.0 match HTTP version 1.0
HTTP_1.1 req_ver 1.1 match HTTP version 1.1
HTTP_CONTENT hdr_val(content-length) gt 0 match an existing content-length
HTTP_URL_ABS url_reg ^[^/:]*:// match absolute URL with scheme
HTTP_URL_SLASH url_beg / match URL beginning with "/"
HTTP_URL_STAR url * match URL equal to "*"
LOCALHOST src 127.0.0.1/8 match connection from local host
METH_CONNECT method CONNECT match HTTP CONNECT method
METH_GET method GET HEAD match HTTP GET or HEAD method
METH_HEAD method HEAD match HTTP HEAD method
METH_OPTIONS method OPTIONS match HTTP OPTIONS method
METH_POST method POST match HTTP POST method
METH_TRACE method TRACE match HTTP TRACE method
RDP_COOKIE req_rdp_cookie_cnt gt 0 match presence of an RDP cookie
REQ_CONTENT req_len gt 0 match data in the request buffer
TRUE always_true always match
WAIT_END wait_end wait for end of content analysis

One of HAProxy's strong points certainly lies is its precise logs. It probably provides the finest level of information available for such a product, which is very important for troubleshooting complex environments. Standard information provided in logs include client ports, TCP/HTTP state timers, precise session state at termination and precise termination cause, information about decisions to direct traffic to a server, and of course the ability to capture arbitrary headers. In order to improve administrators reactivity, it offers a great transparency about encountered problems, both internal and external, and it is possible to send logs to different sources at the same time with different level filters : - global process-level logs (system errors, start/stop, etc..) - per-instance system and internal errors (lack of resource, bugs, ...) - per-instance external troubles (servers up/down, max connections) - per-instance activity (client connections), either at the establishment or at the termination. The ability to distribute different levels of logs to different log servers allow several production teams to interact and to fix their problems as soon as possible. For example, the system team might monitor system-wide errors, while the application team might be monitoring the up/down for their servers in real time, and the security team might analyze the activity logs with one hour delay.

8.1. Log levels

TCP and HTTP connections can be logged with information such as the date, time, source IP address, destination address, connection duration, response times, HTTP request, HTTP return code, number of bytes transmitted, conditions in which the session ended, and even exchanged cookies values. For example track a particular user's problems. All messages may be sent to up to two syslog servers. Check the "log" keyword in section 4.2 for more information about log facilities.

8.2. Log formats

HAProxy supports 5 log formats. Several fields are common between these formats and will be detailed in the following sections. A few of them may vary slightly with the configuration, due to indicators specific to certain options. The supported formats are as follows : - the default format, which is very basic and very rarely used. It only provides very basic information about the incoming connection at the moment it is accepted : source IP:port, destination IP:port, and frontend-name. This mode will eventually disappear so it will not be described to great extents. - the TCP format, which is more advanced. This format is enabled when "option tcplog" is set on the frontend. HAProxy will then usually wait for the connection to terminate before logging. This format provides much richer information, such as timers, connection counts, queue size, etc... This format is recommended for pure TCP proxies. - the HTTP format, which is the most advanced for HTTP proxying. This format is enabled when "option httplog" is set on the frontend. It provides the same information as the TCP format with some HTTP-specific fields such as the request, the status code, and captures of headers and cookies. This format is recommended for HTTP proxies. - the CLF HTTP format, which is equivalent to the HTTP format, but with the fields arranged in the same order as the CLF format. In this mode, all timers, captures, flags, etc... appear one per field after the end of the common fields, in the same order they appear in the standard HTTP format. - the custom log format, allows you to make your own log line. Next sections will go deeper into details for each of these formats. Format specification will be performed on a "field" basis. Unless stated otherwise, a field is a portion of text delimited by any number of spaces. Since syslog servers are susceptible of inserting fields at the beginning of a line, it is always assumed that the first field is the one containing the process name and identifier. Note : Since log lines may be quite long, the log examples in sections below might be broken into multiple lines. The example log lines will be prefixed with 3 closing angle brackets ('>>>') and each time a log is broken into multiple lines, each non-final line will end with a backslash ('') and the next line will start indented by two characters.

8.2.1. Default log format

This format is used when no specific option is set. The log is emitted as soon as the connection is accepted. One should note that this currently is the only format which logs the request's destination IP and ports. Example : listen www mode http log global server srv1 127.0.0.1:8000 >>> Feb 6 12:12:09 localhost haproxy[14385]: Connect from 10.0.1.2:33312 to 10.0.3.31:8012 (www/HTTP) Field Format Extract from the example above 1 process_name '[' pid ']:' haproxy[14385]: 2 'Connect from' Connect from 3 source_ip ':' source_port 10.0.1.2:33312 4 'to' to 5 destination_ip ':' destination_port 10.0.3.31:8012 6 '(' frontend_name '/' mode ')' (www/HTTP) Detailed fields description : - "source_ip" is the IP address of the client which initiated the connection. - "source_port" is the TCP port of the client which initiated the connection. - "destination_ip" is the IP address the client connected to. - "destination_port" is the TCP port the client connected to. - "frontend_name" is the name of the frontend (or listener) which received and processed the connection. - "mode is the mode the frontend is operating (TCP or HTTP). In case of a UNIX socket, the source and destination addresses are marked as "unix:" and the ports reflect the internal ID of the socket which accepted the connection (the same ID as reported in the stats). It is advised not to use this deprecated format for newer installations as it will eventually disappear.

8.2.2. TCP log format

The TCP format is used when "option tcplog" is specified in the frontend, and is the recommended format for pure TCP proxies. It provides a lot of precious information for troubleshooting. Since this format includes timers and byte counts, the log is normally emitted at the end of the session. It can be emitted earlier if "option logasap" is specified, which makes sense in most environments with long sessions such as remote terminals. Sessions which match the "monitor" rules are never logged. It is also possible not to emit logs for sessions for which no data were exchanged between the client and the server, by specifying "option dontlognull" in the frontend. Successful connections will not be logged if "option dontlog-normal" is specified in the frontend. A few fields may slightly vary depending on some configuration options, those are marked with a star ('*') after the field name below. Example : frontend fnt mode tcp option tcplog log global default_backend bck backend bck server srv1 127.0.0.1:8000 >>> Feb 6 12:12:56 localhost haproxy[14387]: 10.0.1.2:33313 [06/Feb/2009:12:12:51.443] fnt bck/srv1 0/0/5007 212 -- 0/0/0/0/3 0/0 Field Format Extract from the example above 1 process_name '[' pid ']:' haproxy[14387]: 2 client_ip ':' client_port 10.0.1.2:33313 3 '[' accept_date ']' [06/Feb/2009:12:12:51.443] 4 frontend_name fnt 5 backend_name '/' server_name bck/srv1 6 Tw '/' Tc '/' Tt* 0/0/5007 7 bytes_read* 212 8 termination_state -- 9 actconn '/' feconn '/' beconn '/' srv_conn '/' retries* 0/0/0/0/3 10 srv_queue '/' backend_queue 0/0 Detailed fields description : - "client_ip" is the IP address of the client which initiated the TCP connection to haproxy. If the connection was accepted on a UNIX socket instead, the IP address would be replaced with the word "unix". Note that when the connection is accepted on a socket configured with "accept-proxy" and the PROXY protocol is correctly used, then the logs will reflect the forwarded connection's information. - "client_port" is the TCP port of the client which initiated the connection. If the connection was accepted on a UNIX socket instead, the port would be replaced with the ID of the accepting socket, which is also reported in the stats interface. - "accept_date" is the exact date when the connection was received by haproxy (which might be very slightly different from the date observed on the network if there was some queuing in the system's backlog). This is usually the same date which may appear in any upstream firewall's log. - "frontend_name" is the name of the frontend (or listener) which received and processed the connection. - "backend_name" is the name of the backend (or listener) which was selected to manage the connection to the server. This will be the same as the frontend if no switching rule has been applied, which is common for TCP applications. - "server_name" is the name of the last server to which the connection was sent, which might differ from the first one if there were connection errors and a redispatch occurred. Note that this server belongs to the backend which processed the request. If the connection was aborted before reaching a server, "" is indicated instead of a server name. - "Tw" is the total time in milliseconds spent waiting in the various queues. It can be "-1" if the connection was aborted before reaching the queue. See "Timers" below for more details. - "Tc" is the total time in milliseconds spent waiting for the connection to establish to the final server, including retries. It can be "-1" if the connection was aborted before a connection could be established. See "Timers" below for more details. - "Tt" is the total time in milliseconds elapsed between the accept and the last close. It covers all possible processing. There is one exception, if "option logasap" was specified, then the time counting stops at the moment the log is emitted. In this case, a '+' sign is prepended before the value, indicating that the final one will be larger. See "Timers" below for more details. - "bytes_read" is the total number of bytes transmitted from the server to the client when the log is emitted. If "option logasap" is specified, the this value will be prefixed with a '+' sign indicating that the final one may be larger. Please note that this value is a 64-bit counter, so log analysis tools must be able to handle it without overflowing. - "termination_state" is the condition the session was in when the session ended. This indicates the session state, which side caused the end of session to happen, and for what reason (timeout, error, ...). The normal flags should be "--", indicating the session was closed by either end with no data remaining in buffers. See below "Session state at disconnection" for more details. - "actconn" is the total number of concurrent connections on the process when the session was logged. It is useful to detect when some per-process system limits have been reached. For instance, if actconn is close to 512 when multiple connection errors occur, chances are high that the system limits the process to use a maximum of 1024 file descriptors and that all of them are used. See section 3 "Global parameters" to find how to tune the system. - "feconn" is the total number of concurrent connections on the frontend when the session was logged. It is useful to estimate the amount of resource required to sustain high loads, and to detect when the frontend's "maxconn" has been reached. Most often when this value increases by huge jumps, it is because there is congestion on the backend servers, but sometimes it can be caused by a denial of service attack. - "beconn" is the total number of concurrent connections handled by the backend when the session was logged. It includes the total number of concurrent connections active on servers as well as the number of connections pending in queues. It is useful to estimate the amount of additional servers needed to support high loads for a given application. Most often when this value increases by huge jumps, it is because there is congestion on the backend servers, but sometimes it can be caused by a denial of service attack. - "srv_conn" is the total number of concurrent connections still active on the server when the session was logged. It can never exceed the server's configured "maxconn" parameter. If this value is very often close or equal to the server's "maxconn", it means that traffic regulation is involved a lot, meaning that either the server's maxconn value is too low, or that there aren't enough servers to process the load with an optimal response time. When only one of the server's "srv_conn" is high, it usually means that this server has some trouble causing the connections to take longer to be processed than on other servers. - "retries" is the number of connection retries experienced by this session when trying to connect to the server. It must normally be zero, unless a server is being stopped at the same moment the connection was attempted. Frequent retries generally indicate either a network problem between haproxy and the server, or a misconfigured system backlog on the server preventing new connections from being queued. This field may optionally be prefixed with a '+' sign, indicating that the session has experienced a redispatch after the maximal retry count has been reached on the initial server. In this case, the server name appearing in the log is the one the connection was redispatched to, and not the first one, though both may sometimes be the same in case of hashing for instance. So as a general rule of thumb, when a '+' is present in front of the retry count, this count should not be attributed to the logged server. - "srv_queue" is the total number of requests which were processed before this one in the server queue. It is zero when the request has not gone through the server queue. It makes it possible to estimate the approximate server's response time by dividing the time spent in queue by the number of requests in the queue. It is worth noting that if a session experiences a redispatch and passes through two server queues, their positions will be cumulated. A request should not pass through both the server queue and the backend queue unless a redispatch occurs. - "backend_queue" is the total number of requests which were processed before this one in the backend's global queue. It is zero when the request has not gone through the global queue. It makes it possible to estimate the average queue length, which easily translates into a number of missing servers when divided by a server's "maxconn" parameter. It is worth noting that if a session experiences a redispatch, it may pass twice in the backend's queue, and then both positions will be cumulated. A request should not pass through both the server queue and the backend queue unless a redispatch occurs.

8.2.3. HTTP log format

The HTTP format is the most complete and the best suited for HTTP proxies. It is enabled by when "option httplog" is specified in the frontend. It provides the same level of information as the TCP format with additional features which are specific to the HTTP protocol. Just like the TCP format, the log is usually emitted at the end of the session, unless "option logasap" is specified, which generally only makes sense for download sites. A session which matches the "monitor" rules will never logged. It is also possible not to log sessions for which no data were sent by the client by specifying "option dontlognull" in the frontend. Successful connections will not be logged if "option dontlog-normal" is specified in the frontend. Most fields are shared with the TCP log, some being different. A few fields may slightly vary depending on some configuration options. Those ones are marked with a star ('*') after the field name below. Example : frontend http-in mode http option httplog log global default_backend bck backend static server srv1 127.0.0.1:8000 >>> Feb 6 12:14:14 localhost haproxy[14389]: 10.0.1.2:33317 [06/Feb/2009:12:14:14.655] http-in static/srv1 10/0/30/69/109 200 2750 - - ---- 1/1/1/1/0 0/0 {1wt.eu} {} "GET /index.html HTTP/1.1" Field Format Extract from the example above 1 process_name '[' pid ']:' haproxy[14389]: 2 client_ip ':' client_port 10.0.1.2:33317 3 '[' accept_date ']' [06/Feb/2009:12:14:14.655] 4 frontend_name http-in 5 backend_name '/' server_name static/srv1 6 Tq '/' Tw '/' Tc '/' Tr '/' Tt* 10/0/30/69/109 7 status_code 200 8 bytes_read* 2750 9 captured_request_cookie - 10 captured_response_cookie - 11 termination_state ---- 12 actconn '/' feconn '/' beconn '/' srv_conn '/' retries* 1/1/1/1/0 13 srv_queue '/' backend_queue 0/0 14 '{' captured_request_headers* '}' {haproxy.1wt.eu} 15 '{' captured_response_headers* '}' {} 16 '"' http_request '"' "GET /index.html HTTP/1.1" Detailed fields description : - "client_ip" is the IP address of the client which initiated the TCP connection to haproxy. If the connection was accepted on a UNIX socket instead, the IP address would be replaced with the word "unix". Note that when the connection is accepted on a socket configured with "accept-proxy" and the PROXY protocol is correctly used, then the logs will reflect the forwarded connection's information. - "client_port" is the TCP port of the client which initiated the connection. If the connection was accepted on a UNIX socket instead, the port would be replaced with the ID of the accepting socket, which is also reported in the stats interface. - "accept_date" is the exact date when the TCP connection was received by haproxy (which might be very slightly different from the date observed on the network if there was some queuing in the system's backlog). This is usually the same date which may appear in any upstream firewall's log. This does not depend on the fact that the client has sent the request or not. - "frontend_name" is the name of the frontend (or listener) which received and processed the connection. - "backend_name" is the name of the backend (or listener) which was selected to manage the connection to the server. This will be the same as the frontend if no switching rule has been applied. - "server_name" is the name of the last server to which the connection was sent, which might differ from the first one if there were connection errors and a redispatch occurred. Note that this server belongs to the backend which processed the request. If the request was aborted before reaching a server, "" is indicated instead of a server name. If the request was intercepted by the stats subsystem, "" is indicated instead. - "Tq" is the total time in milliseconds spent waiting for the client to send a full HTTP request, not counting data. It can be "-1" if the connection was aborted before a complete request could be received. It should always be very small because a request generally fits in one single packet. Large times here generally indicate network trouble between the client and haproxy. See "Timers" below for more details. - "Tw" is the total time in milliseconds spent waiting in the various queues. It can be "-1" if the connection was aborted before reaching the queue. See "Timers" below for more details. - "Tc" is the total time in milliseconds spent waiting for the connection to establish to the final server, including retries. It can be "-1" if the request was aborted before a connection could be established. See "Timers" below for more details. - "Tr" is the total time in milliseconds spent waiting for the server to send a full HTTP response, not counting data. It can be "-1" if the request was aborted before a complete response could be received. It generally matches the server's processing time for the request, though it may be altered by the amount of data sent by the client to the server. Large times here on "GET" requests generally indicate an overloaded server. See "Timers" below for more details. - "Tt" is the total time in milliseconds elapsed between the accept and the last close. It covers all possible processing. There is one exception, if "option logasap" was specified, then the time counting stops at the moment the log is emitted. In this case, a '+' sign is prepended before the value, indicating that the final one will be larger. See "Timers" below for more details. - "status_code" is the HTTP status code returned to the client. This status is generally set by the server, but it might also be set by haproxy when the server cannot be reached or when its response is blocked by haproxy. - "bytes_read" is the total number of bytes transmitted to the client when the log is emitted. This does include HTTP headers. If "option logasap" is specified, the this value will be prefixed with a '+' sign indicating that the final one may be larger. Please note that this value is a 64-bit counter, so log analysis tools must be able to handle it without overflowing. - "captured_request_cookie" is an optional "name=value" entry indicating that the client had this cookie in the request. The cookie name and its maximum length are defined by the "capture cookie" statement in the frontend configuration. The field is a single dash ('-') when the option is not set. Only one cookie may be captured, it is generally used to track session ID exchanges between a client and a server to detect session crossing between clients due to application bugs. For more details, please consult the section "Capturing HTTP headers and cookies" below. - "captured_response_cookie" is an optional "name=value" entry indicating that the server has returned a cookie with its response. The cookie name and its maximum length are defined by the "capture cookie" statement in the frontend configuration. The field is a single dash ('-') when the option is not set. Only one cookie may be captured, it is generally used to track session ID exchanges between a client and a server to detect session crossing between clients due to application bugs. For more details, please consult the section "Capturing HTTP headers and cookies" below. - "termination_state" is the condition the session was in when the session ended. This indicates the session state, which side caused the end of session to happen, for what reason (timeout, error, ...), just like in TCP logs, and information about persistence operations on cookies in the last two characters. The normal flags should begin with "--", indicating the session was closed by either end with no data remaining in buffers. See below "Session state at disconnection" for more details. - "actconn" is the total number of concurrent connections on the process when the session was logged. It is useful to detect when some per-process system limits have been reached. For instance, if actconn is close to 512 or 1024 when multiple connection errors occur, chances are high that the system limits the process to use a maximum of 1024 file descriptors and that all of them are used. See section 3 "Global parameters" to find how to tune the system. - "feconn" is the total number of concurrent connections on the frontend when the session was logged. It is useful to estimate the amount of resource required to sustain high loads, and to detect when the frontend's "maxconn" has been reached. Most often when this value increases by huge jumps, it is because there is congestion on the backend servers, but sometimes it can be caused by a denial of service attack. - "beconn" is the total number of concurrent connections handled by the backend when the session was logged. It includes the total number of concurrent connections active on servers as well as the number of connections pending in queues. It is useful to estimate the amount of additional servers needed to support high loads for a given application. Most often when this value increases by huge jumps, it is because there is congestion on the backend servers, but sometimes it can be caused by a denial of service attack. - "srv_conn" is the total number of concurrent connections still active on the server when the session was logged. It can never exceed the server's configured "maxconn" parameter. If this value is very often close or equal to the server's "maxconn", it means that traffic regulation is involved a lot, meaning that either the server's maxconn value is too low, or that there aren't enough servers to process the load with an optimal response time. When only one of the server's "srv_conn" is high, it usually means that this server has some trouble causing the requests to take longer to be processed than on other servers. - "retries" is the number of connection retries experienced by this session when trying to connect to the server. It must normally be zero, unless a server is being stopped at the same moment the connection was attempted. Frequent retries generally indicate either a network problem between haproxy and the server, or a misconfigured system backlog on the server preventing new connections from being queued. This field may optionally be prefixed with a '+' sign, indicating that the session has experienced a redispatch after the maximal retry count has been reached on the initial server. In this case, the server name appearing in the log is the one the connection was redispatched to, and not the first one, though both may sometimes be the same in case of hashing for instance. So as a general rule of thumb, when a '+' is present in front of the retry count, this count should not be attributed to the logged server. - "srv_queue" is the total number of requests which were processed before this one in the server queue. It is zero when the request has not gone through the server queue. It makes it possible to estimate the approximate server's response time by dividing the time spent in queue by the number of requests in the queue. It is worth noting that if a session experiences a redispatch and passes through two server queues, their positions will be cumulated. A request should not pass through both the server queue and the backend queue unless a redispatch occurs. - "backend_queue" is the total number of requests which were processed before this one in the backend's global queue. It is zero when the request has not gone through the global queue. It makes it possible to estimate the average queue length, which easily translates into a number of missing servers when divided by a server's "maxconn" parameter. It is worth noting that if a session experiences a redispatch, it may pass twice in the backend's queue, and then both positions will be cumulated. A request should not pass through both the server queue and the backend queue unless a redispatch occurs. - "captured_request_headers" is a list of headers captured in the request due to the presence of the "capture request header" statement in the frontend. Multiple headers can be captured, they will be delimited by a vertical bar ('|'). When no capture is enabled, the braces do not appear, causing a shift of remaining fields. It is important to note that this field may contain spaces, and that using it requires a smarter log parser than when it's not used. Please consult the section "Capturing HTTP headers and cookies" below for more details. - "captured_response_headers" is a list of headers captured in the response due to the presence of the "capture response header" statement in the frontend. Multiple headers can be captured, they will be delimited by a vertical bar ('|'). When no capture is enabled, the braces do not appear, causing a shift of remaining fields. It is important to note that this field may contain spaces, and that using it requires a smarter log parser than when it's not used. Please consult the section "Capturing HTTP headers and cookies" below for more details. - "http_request" is the complete HTTP request line, including the method, request and HTTP version string. Non-printable characters are encoded (see below the section "Non-printable characters"). This is always the last field, and it is always delimited by quotes and is the only one which can contain quotes. If new fields are added to the log format, they will be added before this field. This field might be truncated if the request is huge and does not fit in the standard syslog buffer (1024 characters). This is the reason why this field must always remain the last one.

8.2.4. Custom log format

The directive log-format allows you to customize the logs in http mode and tcp mode. It takes a string as argument. HAproxy understands some log format variables. % precedes log format variables. Variables can take arguments using braces ('{}'), and multiple arguments are separated by commas within the braces. Flags may be added or removed by prefixing them with a '+' or '-' sign. Special variable "%o" may be used to propagate its flags to all other variables on the same format string. This is particularly handy with quoted string formats ("Q"). If a variable is named between square brackets ('[' .. ']') then it is used as a sample expression rule (see section 7.3). This it useful to add some less common information such as the client's SSL certificate's DN, or to log the key that would be used to store an entry into a stick table. Note: spaces must be escaped. A space character is considered as a separator. In order to emit a verbatim '%', it must be preceded by another '%' resulting in '%%'. HAProxy will automatically merge consecutive separators. Flags are : * Q: quote a string * X: hexadecimal representation (IPs, Ports, %Ts, %rt, %pid) Example: log-format %T %t Some Text log-format %{+Q}o %t %s %{-Q}r At the moment, the default HTTP format is defined this way : log-format %ci:%cp [%t] %ft %b/%s %Tq/%Tw/%Tc/%Tr/%Tt %ST %B %CC %CS %tsc %ac/%fc/%bc/%sc/%rc %sq/%bq %hr %hs %{+Q}r the default CLF format is defined this way : log-format %{+Q}o %{-Q}ci - - [%T] %r %ST %B "" "" %cp %ms %ft %b %s %Tq %Tw %Tc %Tr %Tt %tsc %ac %fc %bc %sc %rc %sq %bq %CC %CS %hrl %hsl and the default TCP format is defined this way : log-format %ci:%cp [%t] %ft %b/%s %Tw/%Tc/%Tt %B %ts %ac/%fc/%bc/%sc/%rc %sq/%bq Please refer to the table below for currently defined variables : +---+------+-----------------------------------------------+-------------+ | R | var | field name (8.2.2 and 8.2.3 for description) | type | +---+------+-----------------------------------------------+-------------+ | | %o | special variable, apply flags on all next var | | +---+------+-----------------------------------------------+-------------+ | | %B | bytes_read (from server to client) | numeric | | H | %CC | captured_request_cookie | string | | H | %CS | captured_response_cookie | string | | | %H | hostname | string | | | %ID | unique-id | string | | | %ST | status_code | numeric | | | %T | gmt_date_time | date | | | %Tc | Tc | numeric | | | %Tl | local_date_time | date | | H | %Tq | Tq | numeric | | H | %Tr | Tr | numeric | | | %Ts | timestamp | numeric | | | %Tt | Tt | numeric | | | %Tw | Tw | numeric | | | %U | bytes_uploaded (from client to server) | numeric | | | %ac | actconn | numeric | | | %b | backend_name | string | | | %bc | beconn (backend concurrent connections) | numeric | | | %bi | backend_source_ip (connecting address) | IP | | | %bp | backend_source_port (connecting address) | numeric | | | %bq | backend_queue | numeric | | | %ci | client_ip (accepted address) | IP | | | %cp | client_port (accepted address) | numeric | | | %f | frontend_name | string | | | %fc | feconn (frontend concurrent connections) | numeric | | | %fi | frontend_ip (accepting address) | IP | | | %fp | frontend_port (accepting address) | numeric | | | %ft | frontend_name_transport ('~' suffix for SSL) | string | | | %hr | captured_request_headers default style | string | | | %hrl | captured_request_headers CLF style | string list | | | %hs | captured_response_headers default style | string | | | %hsl | captured_response_headers CLF style | string list | | | %ms | accept date milliseconds (left-padded with 0) | numeric | | | %pid | PID | numeric | | H | %r | http_request | string | | | %rc | retries | numeric | | | %rt | request_counter (HTTP req or TCP session) | numeric | | | %s | server_name | string | | | %sc | srv_conn (server concurrent connections) | numeric | | | %si | server_IP (target address) | IP | | | %sp | server_port (target address) | numeric | | | %sq | srv_queue | numeric | | S | %sslc| ssl_ciphers (ex: AES-SHA) | string | | S | %sslv| ssl_version (ex: TLSv1) | string | | | %t | date_time (with millisecond resolution) | date | | | %ts | termination_state | string | | H | %tsc | termination_state with cookie status | string | +---+------+-----------------------------------------------+-------------+ R = Restrictions : H = mode http only ; S = SSL only

8.2.5. Error log format

When an incoming connection fails due to an SSL handshake or an invalid PROXY protocol header, haproxy will log the event using a shorter, fixed line format. By default, logs are emitted at the LOG_INFO level, unless the option "log-separate-errors" is set in the backend, in which case the LOG_ERR level will be used. Connections on which no data are exchanged (eg: probes) are not logged if the "dontlognull" option is set. The format looks like this : >>> Dec 3 18:27:14 localhost haproxy[6103]: 127.0.0.1:56059 [03/Dec/2012:17:35:10.380] frt/f1: Connection error during SSL handshake Field Format Extract from the example above 1 process_name '[' pid ']:' haproxy[6103]: 2 client_ip ':' client_port 127.0.0.1:56059 3 '[' accept_date ']' [03/Dec/2012:17:35:10.380] 4 frontend_name "/" bind_name ":" frt/f1: 5 message Connection error during SSL handshake These fields just provide minimal information to help debugging connection failures.

8.3. Advanced logging options

Some advanced logging options are often looked for but are not easy to find out just by looking at the various options. Here is an entry point for the few options which can enable better logging. Please refer to the keywords reference for more information about their usage.

8.3.1. Disabling logging of external tests

It is quite common to have some monitoring tools perform health checks on haproxy. Sometimes it will be a layer 3 load-balancer such as LVS or any commercial load-balancer, and sometimes it will simply be a more complete monitoring system such as Nagios. When the tests are very frequent, users often ask how to disable logging for those checks. There are three possibilities : - if connections come from everywhere and are just TCP probes, it is often desired to simply disable logging of connections without data exchange, by setting "option dontlognull" in the frontend. It also disables logging of port scans, which may or may not be desired. - if the connection come from a known source network, use "monitor-net" to declare this network as monitoring only. Any host in this network will then only be able to perform health checks, and their requests will not be logged. This is generally appropriate to designate a list of equipment such as other load-balancers. - if the tests are performed on a known URI, use "monitor-uri" to declare this URI as dedicated to monitoring. Any host sending this request will only get the result of a health-check, and the request will not be logged.

8.3.2. Logging before waiting for the session to terminate

The problem with logging at end of connection is that you have no clue about what is happening during very long sessions, such as remote terminal sessions or large file downloads. This problem can be worked around by specifying "option logasap" in the frontend. Haproxy will then log as soon as possible, just before data transfer begins. This means that in case of TCP, it will still log the connection status to the server, and in case of HTTP, it will log just after processing the server headers. In this case, the number of bytes reported is the number of header bytes sent to the client. In order to avoid confusion with normal logs, the total time field and the number of bytes are prefixed with a '+' sign which means that real numbers are certainly larger.

8.3.3. Raising log level upon errors

Sometimes it is more convenient to separate normal traffic from errors logs, for instance in order to ease error monitoring from log files. When the option "log-separate-errors" is used, connections which experience errors, timeouts, retries, redispatches or HTTP status codes 5xx will see their syslog level raised from "info" to "err". This will help a syslog daemon store the log in a separate file. It is very important to keep the errors in the normal traffic file too, so that log ordering is not altered. You should also be careful if you already have configured your syslog daemon to store all logs higher than "notice" in an "admin" file, because the "err" level is higher than "notice".

8.3.4. Disabling logging of successful connections

Although this may sound strange at first, some large sites have to deal with multiple thousands of logs per second and are experiencing difficulties keeping them intact for a long time or detecting errors within them. If the option "dontlog-normal" is set on the frontend, all normal connections will not be logged. In this regard, a normal connection is defined as one without any error, timeout, retry nor redispatch. In HTTP, the status code is checked too, and a response with a status 5xx is not considered normal and will be logged too. Of course, doing is is really discouraged as it will remove most of the useful information from the logs. Do this only if you have no other alternative.

8.4. Timing events

Timers provide a great help in troubleshooting network problems. All values are reported in milliseconds (ms). These timers should be used in conjunction with the session termination flags. In TCP mode with "option tcplog" set on the frontend, 3 control points are reported under the form "Tw/Tc/Tt", and in HTTP mode, 5 control points are reported under the form "Tq/Tw/Tc/Tr/Tt" : - Tq: total time to get the client request (HTTP mode only). It's the time elapsed between the moment the client connection was accepted and the moment the proxy received the last HTTP header. The value "-1" indicates that the end of headers (empty line) has never been seen. This happens when the client closes prematurely or times out. - Tw: total time spent in the queues waiting for a connection slot. It accounts for backend queue as well as the server queues, and depends on the queue size, and the time needed for the server to complete previous requests. The value "-1" means that the request was killed before reaching the queue, which is generally what happens with invalid or denied requests. - Tc: total time to establish the TCP connection to the server. It's the time elapsed between the moment the proxy sent the connection request, and the moment it was acknowledged by the server, or between the TCP SYN packet and the matching SYN/ACK packet in return. The value "-1" means that the connection never established. - Tr: server response time (HTTP mode only). It's the time elapsed between the moment the TCP connection was established to the server and the moment the server sent its complete response headers. It purely shows its request processing time, without the network overhead due to the data transmission. It is worth noting that when the client has data to send to the server, for instance during a POST request, the time already runs, and this can distort apparent response time. For this reason, it's generally wise not to trust too much this field for POST requests initiated from clients behind an untrusted network. A value of "-1" here means that the last the response header (empty line) was never seen, most likely because the server timeout stroke before the server managed to process the request. - Tt: total session duration time, between the moment the proxy accepted it and the moment both ends were closed. The exception is when the "logasap" option is specified. In this case, it only equals (Tq+Tw+Tc+Tr), and is prefixed with a '+' sign. From this field, we can deduce "Td", the data transmission time, by subtracting other timers when valid : Td = Tt - (Tq + Tw + Tc + Tr) Timers with "-1" values have to be excluded from this equation. In TCP mode, "Tq" and "Tr" have to be excluded too. Note that "Tt" can never be negative. These timers provide precious indications on trouble causes. Since the TCP protocol defines retransmit delays of 3, 6, 12... seconds, we know for sure that timers close to multiples of 3s are nearly always related to lost packets due to network problems (wires, negotiation, congestion). Moreover, if "Tt" is close to a timeout value specified in the configuration, it often means that a session has been aborted on timeout. Most common cases : - If "Tq" is close to 3000, a packet has probably been lost between the client and the proxy. This is very rare on local networks but might happen when clients are on far remote networks and send large requests. It may happen that values larger than usual appear here without any network cause. Sometimes, during an attack or just after a resource starvation has ended, haproxy may accept thousands of connections in a few milliseconds. The time spent accepting these connections will inevitably slightly delay processing of other connections, and it can happen that request times in the order of a few tens of milliseconds are measured after a few thousands of new connections have been accepted at once. Using one of the keep-alive modes may display larger request times since "Tq" also measures the time spent waiting for additional requests. - If "Tc" is close to 3000, a packet has probably been lost between the server and the proxy during the server connection phase. This value should always be very low, such as 1 ms on local networks and less than a few tens of ms on remote networks. - If "Tr" is nearly always lower than 3000 except some rare values which seem to be the average majored by 3000, there are probably some packets lost between the proxy and the server. - If "Tt" is large even for small byte counts, it generally is because neither the client nor the server decides to close the connection, for instance because both have agreed on a keep-alive connection mode. In order to solve this issue, it will be needed to specify "option httpclose" on either the frontend or the backend. If the problem persists, it means that the server ignores the "close" connection mode and expects the client to close. Then it will be required to use "option forceclose". Having the smallest possible 'Tt' is important when connection regulation is used with the "maxconn" option on the servers, since no new connection will be sent to the server until another one is released. Other noticeable HTTP log cases ('xx' means any value to be ignored) : Tq/Tw/Tc/Tr/+Tt The "option logasap" is present on the frontend and the log was emitted before the data phase. All the timers are valid except "Tt" which is shorter than reality. -1/xx/xx/xx/Tt The client was not able to send a complete request in time or it aborted too early. Check the session termination flags then "timeout http-request" and "timeout client" settings. Tq/-1/xx/xx/Tt It was not possible to process the request, maybe because servers were out of order, because the request was invalid or forbidden by ACL rules. Check the session termination flags. Tq/Tw/-1/xx/Tt The connection could not establish on the server. Either it actively refused it or it timed out after Tt-(Tq+Tw) ms. Check the session termination flags, then check the "timeout connect" setting. Note that the tarpit action might return similar-looking patterns, with "Tw" equal to the time the client connection was maintained open. Tq/Tw/Tc/-1/Tt The server has accepted the connection but did not return a complete response in time, or it closed its connection unexpectedly after Tt-(Tq+Tw+Tc) ms. Check the session termination flags, then check the "timeout server" setting.

8.5. Session state at disconnection

TCP and HTTP logs provide a session termination indicator in the "termination_state" field, just before the number of active connections. It is 2-characters long in TCP mode, and is extended to 4 characters in HTTP mode, each of which has a special meaning : - On the first character, a code reporting the first event which caused the session to terminate : C : the TCP session was unexpectedly aborted by the client. S : the TCP session was unexpectedly aborted by the server, or the server explicitly refused it. P : the session was prematurely aborted by the proxy, because of a connection limit enforcement, because a DENY filter was matched, because of a security check which detected and blocked a dangerous error in server response which might have caused information leak (eg: cacheable cookie). L : the session was locally processed by haproxy and was not passed to a server. This is what happens for stats and redirects. R : a resource on the proxy has been exhausted (memory, sockets, source ports, ...). Usually, this appears during the connection phase, and system logs should contain a copy of the precise error. If this happens, it must be considered as a very serious anomaly which should be fixed as soon as possible by any means. I : an internal error was identified by the proxy during a self-check. This should NEVER happen, and you are encouraged to report any log containing this, because this would almost certainly be a bug. It would be wise to preventively restart the process after such an event too, in case it would be caused by memory corruption. D : the session was killed by haproxy because the server was detected as down and was configured to kill all connections when going down. U : the session was killed by haproxy on this backup server because an active server was detected as up and was configured to kill all backup connections when going up. K : the session was actively killed by an admin operating on haproxy. c : the client-side timeout expired while waiting for the client to send or receive data. s : the server-side timeout expired while waiting for the server to send or receive data. - : normal session completion, both the client and the server closed with nothing left in the buffers. - on the second character, the TCP or HTTP session state when it was closed : R : the proxy was waiting for a complete, valid REQUEST from the client (HTTP mode only). Nothing was sent to any server. Q : the proxy was waiting in the QUEUE for a connection slot. This can only happen when servers have a 'maxconn' parameter set. It can also happen in the global queue after a redispatch consecutive to a failed attempt to connect to a dying server. If no redispatch is reported, then no connection attempt was made to any server. C : the proxy was waiting for the CONNECTION to establish on the server. The server might at most have noticed a connection attempt. H : the proxy was waiting for complete, valid response HEADERS from the server (HTTP only). D : the session was in the DATA phase. L : the proxy was still transmitting LAST data to the client while the server had already finished. This one is very rare as it can only happen when the client dies while receiving the last packets. T : the request was tarpitted. It has been held open with the client during the whole "timeout tarpit" duration or until the client closed, both of which will be reported in the "Tw" timer. - : normal session completion after end of data transfer. - the third character tells whether the persistence cookie was provided by the client (only in HTTP mode) : N : the client provided NO cookie. This is usually the case for new visitors, so counting the number of occurrences of this flag in the logs generally indicate a valid trend for the site frequentation. I : the client provided an INVALID cookie matching no known server. This might be caused by a recent configuration change, mixed cookies between HTTP/HTTPS sites, persistence conditionally ignored, or an attack. D : the client provided a cookie designating a server which was DOWN, so either "option persist" was used and the client was sent to this server, or it was not set and the client was redispatched to another server. V : the client provided a VALID cookie, and was sent to the associated server. E : the client provided a valid cookie, but with a last date which was older than what is allowed by the "maxidle" cookie parameter, so the cookie is consider EXPIRED and is ignored. The request will be redispatched just as if there was no cookie. O : the client provided a valid cookie, but with a first date which was older than what is allowed by the "maxlife" cookie parameter, so the cookie is consider too OLD and is ignored. The request will be redispatched just as if there was no cookie. U : a cookie was present but was not used to select the server because some other server selection mechanism was used instead (typically a "use-server" rule). - : does not apply (no cookie set in configuration). - the last character reports what operations were performed on the persistence cookie returned by the server (only in HTTP mode) : N : NO cookie was provided by the server, and none was inserted either. I : no cookie was provided by the server, and the proxy INSERTED one. Note that in "cookie insert" mode, if the server provides a cookie, it will still be overwritten and reported as "I" here. U : the proxy UPDATED the last date in the cookie that was presented by the client. This can only happen in insert mode with "maxidle". It happens every time there is activity at a different date than the date indicated in the cookie. If any other change happens, such as a redispatch, then the cookie will be marked as inserted instead. P : a cookie was PROVIDED by the server and transmitted as-is. R : the cookie provided by the server was REWRITTEN by the proxy, which happens in "cookie rewrite" or "cookie prefix" modes. D : the cookie provided by the server was DELETED by the proxy. - : does not apply (no cookie set in configuration). The combination of the two first flags gives a lot of information about what was happening when the session terminated, and why it did terminate. It can be helpful to detect server saturation, network troubles, local system resource starvation, attacks, etc... The most common termination flags combinations are indicated below. They are alphabetically sorted, with the lowercase set just after the upper case for easier finding and understanding. Flags Reason -- Normal termination. CC The client aborted before the connection could be established to the server. This can happen when haproxy tries to connect to a recently dead (or unchecked) server, and the client aborts while haproxy is waiting for the server to respond or for "timeout connect" to expire. CD The client unexpectedly aborted during data transfer. This can be caused by a browser crash, by an intermediate equipment between the client and haproxy which decided to actively break the connection, by network routing issues between the client and haproxy, or by a keep-alive session between the server and the client terminated first by the client. cD The client did not send nor acknowledge any data for as long as the "timeout client" delay. This is often caused by network failures on the client side, or the client simply leaving the net uncleanly. CH The client aborted while waiting for the server to start responding. It might be the server taking too long to respond or the client clicking the 'Stop' button too fast. cH The "timeout client" stroke while waiting for client data during a POST request. This is sometimes caused by too large TCP MSS values for PPPoE networks which cannot transport full-sized packets. It can also happen when client timeout is smaller than server timeout and the server takes too long to respond. CQ The client aborted while its session was queued, waiting for a server with enough empty slots to accept it. It might be that either all the servers were saturated or that the assigned server was taking too long a time to respond. CR The client aborted before sending a full HTTP request. Most likely the request was typed by hand using a telnet client, and aborted too early. The HTTP status code is likely a 400 here. Sometimes this might also be caused by an IDS killing the connection between haproxy and the client. "option http-ignore-probes" can be used to ignore connections without any data transfer. cR The "timeout http-request" stroke before the client sent a full HTTP request. This is sometimes caused by too large TCP MSS values on the client side for PPPoE networks which cannot transport full-sized packets, or by clients sending requests by hand and not typing fast enough, or forgetting to enter the empty line at the end of the request. The HTTP status code is likely a 408 here. Note: recently, some browsers started to implement a "pre-connect" feature consisting in speculatively connecting to some recently visited web sites just in case the user would like to visit them. This results in many connections being established to web sites, which end up in 408 Request Timeout if the timeout strikes first, or 400 Bad Request when the browser decides to close them first. These ones pollute the log and feed the error counters. Some versions of some browsers have even been reported to display the error code. It is possible to work around the undesirable effects of this behaviour by adding "option http-ignore-probes" in the frontend, resulting in connections with zero data transfer to be totally ignored. This will definitely hide the errors of people experiencing connectivity issues though. CT The client aborted while its session was tarpitted. It is important to check if this happens on valid requests, in order to be sure that no wrong tarpit rules have been written. If a lot of them happen, it might make sense to lower the "timeout tarpit" value to something closer to the average reported "Tw" timer, in order not to consume resources for just a few attackers. LR The request was intercepted and locally handled by haproxy. Generally it means that this was a redirect or a stats request. SC The server or an equipment between it and haproxy explicitly refused the TCP connection (the proxy received a TCP RST or an ICMP message in return). Under some circumstances, it can also be the network stack telling the proxy that the server is unreachable (eg: no route, or no ARP response on local network). When this happens in HTTP mode, the status code is likely a 502 or 503 here. sC The "timeout connect" stroke before a connection to the server could complete. When this happens in HTTP mode, the status code is likely a 503 or 504 here. SD The connection to the server died with an error during the data transfer. This usually means that haproxy has received an RST from the server or an ICMP message from an intermediate equipment while exchanging data with the server. This can be caused by a server crash or by a network issue on an intermediate equipment. sD The server did not send nor acknowledge any data for as long as the "timeout server" setting during the data phase. This is often caused by too short timeouts on L4 equipments before the server (firewalls, load-balancers, ...), as well as keep-alive sessions maintained between the client and the server expiring first on haproxy. SH The server aborted before sending its full HTTP response headers, or it crashed while processing the request. Since a server aborting at this moment is very rare, it would be wise to inspect its logs to control whether it crashed and why. The logged request may indicate a small set of faulty requests, demonstrating bugs in the application. Sometimes this might also be caused by an IDS killing the connection between haproxy and the server. sH The "timeout server" stroke before the server could return its response headers. This is the most common anomaly, indicating too long transactions, probably caused by server or database saturation. The immediate workaround consists in increasing the "timeout server" setting, but it is important to keep in mind that the user experience will suffer from these long response times. The only long term solution is to fix the application. sQ The session spent too much time in queue and has been expired. See the "timeout queue" and "timeout connect" settings to find out how to fix this if it happens too often. If it often happens massively in short periods, it may indicate general problems on the affected servers due to I/O or database congestion, or saturation caused by external attacks. PC The proxy refused to establish a connection to the server because the process' socket limit has been reached while attempting to connect. The global "maxconn" parameter may be increased in the configuration so that it does not happen anymore. This status is very rare and might happen when the global "ulimit-n" parameter is forced by hand. PD The proxy blocked an incorrectly formatted chunked encoded message in a request or a response, after the server has emitted its headers. In most cases, this will indicate an invalid message from the server to the client. Haproxy supports chunk sizes of up to 2GB - 1 (2147483647 bytes). Any larger size will be considered as an error. PH The proxy blocked the server's response, because it was invalid, incomplete, dangerous (cache control), or matched a security filter. In any case, an HTTP 502 error is sent to the client. One possible cause for this error is an invalid syntax in an HTTP header name containing unauthorized characters. It is also possible but quite rare, that the proxy blocked a chunked-encoding request from the client due to an invalid syntax, before the server responded. In this case, an HTTP 400 error is sent to the client and reported in the logs. PR The proxy blocked the client's HTTP request, either because of an invalid HTTP syntax, in which case it returned an HTTP 400 error to the client, or because a deny filter matched, in which case it returned an HTTP 403 error. PT The proxy blocked the client's request and has tarpitted its connection before returning it a 500 server error. Nothing was sent to the server. The connection was maintained open for as long as reported by the "Tw" timer field. RC A local resource has been exhausted (memory, sockets, source ports) preventing the connection to the server from establishing. The error logs will tell precisely what was missing. This is very rare and can only be solved by proper system tuning. The combination of the two last flags gives a lot of information about how persistence was handled by the client, the server and by haproxy. This is very important to troubleshoot disconnections, when users complain they have to re-authenticate. The commonly encountered flags are : -- Persistence cookie is not enabled. NN No cookie was provided by the client, none was inserted in the response. For instance, this can be in insert mode with "postonly" set on a GET request. II A cookie designating an invalid server was provided by the client, a valid one was inserted in the response. This typically happens when a "server" entry is removed from the configuration, since its cookie value can be presented by a client when no other server knows it. NI No cookie was provided by the client, one was inserted in the response. This typically happens for first requests from every user in "insert" mode, which makes it an easy way to count real users. VN A cookie was provided by the client, none was inserted in the response. This happens for most responses for which the client has already got a cookie. VU A cookie was provided by the client, with a last visit date which is not completely up-to-date, so an updated cookie was provided in response. This can also happen if there was no date at all, or if there was a date but the "maxidle" parameter was not set, so that the cookie can be switched to unlimited time. EI A cookie was provided by the client, with a last visit date which is too old for the "maxidle" parameter, so the cookie was ignored and a new cookie was inserted in the response. OI A cookie was provided by the client, with a first visit date which is too old for the "maxlife" parameter, so the cookie was ignored and a new cookie was inserted in the response. DI The server designated by the cookie was down, a new server was selected and a new cookie was emitted in the response. VI The server designated by the cookie was not marked dead but could not be reached. A redispatch happened and selected another one, which was then advertised in the response.

8.6. Non-printable characters

In order not to cause trouble to log analysis tools or terminals during log consulting, non-printable characters are not sent as-is into log files, but are converted to the two-digits hexadecimal representation of their ASCII code, prefixed by the character '#'. The only characters that can be logged without being escaped are comprised between 32 and 126 (inclusive). Obviously, the escape character '#' itself is also encoded to avoid any ambiguity ("#23"). It is the same for the character '"' which becomes "#22", as well as '{', '|' and '}' when logging headers. Note that the space character (' ') is not encoded in headers, which can cause issues for tools relying on space count to locate fields. A typical header containing spaces is "User-Agent". Last, it has been observed that some syslog daemons such as syslog-ng escape the quote ('"') with a backslash (''). The reverse operation can safely be performed since no quote may appear anywhere else in the logs.

8.7. Capturing HTTP cookies

Cookie capture simplifies the tracking a complete user session. This can be achieved using the "capture cookie" statement in the frontend. Please refer to section 4.2 for more details. Only one cookie can be captured, and the same cookie will simultaneously be checked in the request ("Cookie:" header) and in the response ("Set-Cookie:" header). The respective values will be reported in the HTTP logs at the "captured_request_cookie" and "captured_response_cookie" locations (see section 8.2.3 about HTTP log format). When either cookie is not seen, a dash ('-') replaces the value. This way, it's easy to detect when a user switches to a new session for example, because the server will reassign it a new cookie. It is also possible to detect if a server unexpectedly sets a wrong cookie to a client, leading to session crossing. Examples : capture cookie ASPSESSION len 32 capture cookie vgnvisitor= len 32

8.8. Capturing HTTP headers

Header captures are useful to track unique request identifiers set by an upper proxy, virtual host names, user-agents, POST content-length, referrers, etc. In the response, one can search for information about the response length, how the server asked the cache to behave, or an object location during a redirection. Header captures are performed using the "capture request header" and "capture response header" statements in the frontend. Please consult their definition in section 4.2 for more details. It is possible to include both request headers and response headers at the same time. Non-existent headers are logged as empty strings, and if one header appears more than once, only its last occurrence will be logged. Request headers are grouped within braces '{' and '}' in the same order as they were declared, and delimited with a vertical bar '|' without any space. Response headers follow the same representation, but are displayed after a space following the request headers block. These blocks are displayed just before the HTTP request in the logs. As a special case, it is possible to specify an HTTP header capture in a TCP frontend. The purpose is to enable logging of headers which will be parsed in an HTTP backend if the request is then switched to this HTTP backend. Example : listen proxy-out mode http option httplog option logasap log global server cache1 192.168.1.1:3128 capture request header Host len 20 capture request header Content-Length len 10 capture request header Referer len 20 capture response header Server len 20 capture response header Content-Length len 10 capture response header Cache-Control len 8 capture response header Via len 20 capture response header Location len 20 >>> Aug 9 20:26:09 localhost haproxy[2022]: 127.0.0.1:34014 [09/Aug/2004:20:26:09] proxy-out proxy-out/cache1 0/0/0/162/+162 200 +350 - - ---- 0/0/0/0/0 0/0 {fr.adserver.yahoo.co||http://fr.f416.mail.} {|864|private||} "GET http://fr.adserver.yahoo.com/" >>> Aug 9 20:30:46 localhost haproxy[2022]: 127.0.0.1:34020 [09/Aug/2004:20:30:46] proxy-out proxy-out/cache1 0/0/0/182/+182 200 +279 - - ---- 0/0/0/0/0 0/0 {w.ods.org||} {Formilux/0.1.8|3495|||} "GET http://trafic.1wt.eu/ HTTP/1.1" >>> Aug 9 20:30:46 localhost haproxy[2022]: 127.0.0.1:34028 [09/Aug/2004:20:30:46] proxy-out proxy-out/cache1 0/0/2/126/+128 301 +223 - - ---- 0/0/0/0/0 0/0 {www.sytadin.equipement.gouv.fr||http://trafic.1wt.eu/} {Apache|230|||http://www.sytadin.} "GET http://www.sytadin.equipement.gouv.fr/ HTTP/1.1"

8.9. Examples of logs

These are real-world examples of logs accompanied with an explanation. Some of them have been made up by hand. The syslog part has been removed for better reading. Their sole purpose is to explain how to decipher them. >>> haproxy[674]: 127.0.0.1:33318 [15/Oct/2003:08:31:57.130] px-http px-http/srv1 6559/0/7/147/6723 200 243 - - ---- 5/3/3/1/0 0/0 "HEAD / HTTP/1.0" => long request (6.5s) entered by hand through 'telnet'. The server replied in 147 ms, and the session ended normally ('----') >>> haproxy[674]: 127.0.0.1:33319 [15/Oct/2003:08:31:57.149] px-http px-http/srv1 6559/1230/7/147/6870 200 243 - - ---- 324/239/239/99/0 0/9 "HEAD / HTTP/1.0" => Idem, but the request was queued in the global queue behind 9 other requests, and waited there for 1230 ms. >>> haproxy[674]: 127.0.0.1:33320 [15/Oct/2003:08:32:17.654] px-http px-http/srv1 9/0/7/14/+30 200 +243 - - ---- 3/3/3/1/0 0/0 "GET /image.iso HTTP/1.0" => request for a long data transfer. The "logasap" option was specified, so the log was produced just before transferring data. The server replied in 14 ms, 243 bytes of headers were sent to the client, and total time from accept to first data byte is 30 ms. >>> haproxy[674]: 127.0.0.1:33320 [15/Oct/2003:08:32:17.925] px-http px-http/srv1 9/0/7/14/30 502 243 - - PH-- 3/2/2/0/0 0/0 "GET /cgi-bin/bug.cgi? HTTP/1.0" => the proxy blocked a server response either because of an "rspdeny" or "rspideny" filter, or because the response was improperly formatted and not HTTP-compliant, or because it blocked sensitive information which risked being cached. In this case, the response is replaced with a "502 bad gateway". The flags ("PH--") tell us that it was haproxy who decided to return the 502 and not the server. >>> haproxy[18113]: 127.0.0.1:34548 [15/Oct/2003:15:18:55.798] px-http px-http/ -1/-1/-1/-1/8490 -1 0 - - CR-- 2/2/2/0/0 0/0 "" => the client never completed its request and aborted itself ("C---") after 8.5s, while the proxy was waiting for the request headers ("-R--"). Nothing was sent to any server. >>> haproxy[18113]: 127.0.0.1:34549 [15/Oct/2003:15:19:06.103] px-http px-http/ -1/-1/-1/-1/50001 408 0 - - cR-- 2/2/2/0/0 0/0 "" => The client never completed its request, which was aborted by the time-out ("c---") after 50s, while the proxy was waiting for the request headers ("-R--"). Nothing was sent to any server, but the proxy could send a 408 return code to the client. >>> haproxy[18989]: 127.0.0.1:34550 [15/Oct/2003:15:24:28.312] px-tcp px-tcp/srv1 0/0/5007 0 cD 0/0/0/0/0 0/0 => This log was produced with "option tcplog". The client timed out after 5 seconds ("c----"). >>> haproxy[18989]: 10.0.0.1:34552 [15/Oct/2003:15:26:31.462] px-http px-http/srv1 3183/-1/-1/-1/11215 503 0 - - SC-- 205/202/202/115/3 0/0 "HEAD / HTTP/1.0" => The request took 3s to complete (probably a network problem), and the connection to the server failed ('SC--') after 4 attempts of 2 seconds (config says 'retries 3'), and no redispatch (otherwise we would have seen "/+3"). Status code 503 was returned to the client. There were 115 connections on this server, 202 connections on this proxy, and 205 on the global process. It is possible that the server refused the connection because of too many already established. It is possible to query HAProxy about its status. The most commonly used mechanism is the HTTP statistics page. This page also exposes an alternative CSV output format for monitoring tools. The same format is provided on the Unix socket.

9.1. CSV format

The statistics may be consulted either from the unix socket or from the HTTP page. Both means provide a CSV format whose fields follow. The first line begins with a sharp ('#') and has one word per comma-delimited field which represents the title of the column. All other lines starting at the second one use a classical CSV format using a comma as the delimiter, and the double quote ('"') as an optional text delimiter, but only if the enclosed text is ambiguous (if it contains a quote or a comma). The double-quote character ('"') in the text is doubled ('""'), which is the format that most tools recognize. Please do not insert any column before these ones in order not to break tools which use hard-coded column positions. In brackets after each field name are the types which may have a value for that field. The types are L (Listeners), F (Frontends), B (Backends), and S (Servers). 0. pxname [LFBS]: proxy name 1. svname [LFBS]: service name (FRONTEND for frontend, BACKEND for backend, any name for server/listener) 2. qcur [..BS]: current queued requests. For the backend this reports the number queued without a server assigned. 3. qmax [..BS]: max value of qcur 4. scur [LFBS]: current sessions 5. smax [LFBS]: max sessions 6. slim [LFBS]: configured session limit 7. stot [LFBS]: cumulative number of connections 8. bin [LFBS]: bytes in 9. bout [LFBS]: bytes out 10. dreq [LFB.]: requests denied because of security concerns. - For tcp this is because of a matched tcp-request content rule. - For http this is because of a matched http-request or tarpit rule. 11. dresp [LFBS]: responses denied because of security concerns. - For http this is because of a matched http-request rule, or "option checkcache". 12. ereq [LF..]: request errors. Some of the possible causes are: - early termination from the client, before the request has been sent. - read error from the client - client timeout - client closed connection - various bad requests from the client. - request was tarpitted. 13. econ [..BS]: number of requests that encountered an error trying to connect to a backend server. The backend stat is the sum of the stat for all servers of that backend, plus any connection errors not associated with a particular server (such as the backend having no active servers). 14. eresp [..BS]: response errors. srv_abrt will be counted here also. Some other errors are: - write error on the client socket (won't be counted for the server stat) - failure applying filters to the response. 15. wretr [..BS]: number of times a connection to a server was retried. 16. wredis [..BS]: number of times a request was redispatched to another server. The server value counts the number of times that server was switched away from. 17. status [LFBS]: status (UP/DOWN/NOLB/MAINT/MAINT(via)...) 18. weight [..BS]: total weight (backend), server weight (server) 19. act [..BS]: number of active servers (backend), server is active (server) 20. bck [..BS]: number of backup servers (backend), server is backup (server) 21. chkfail [...S]: number of failed checks. (Only counts checks failed when the server is up.) 22. chkdown [..BS]: number of UP->DOWN transitions. The backend counter counts transitions to the whole backend being down, rather than the sum of the counters for each server. 23. lastchg [..BS]: number of seconds since the last UP<->DOWN transition 24. downtime [..BS]: total downtime (in seconds). The value for the backend is the downtime for the whole backend, not the sum of the server downtime. 25. qlimit [...S]: configured maxqueue for the server, or nothing in the value is 0 (default, meaning no limit) 26. pid [LFBS]: process id (0 for first instance, 1 for second, ...) 27. iid [LFBS]: unique proxy id 28. sid [L..S]: server id (unique inside a proxy) 29. throttle [...S]: current throttle percentage for the server, when slowstart is active, or no value if not in slowstart. 30. lbtot [..BS]: total number of times a server was selected, either for new sessions, or when re-dispatching. The server counter is the number of times that server was selected. 31. tracked [...S]: id of proxy/server if tracking is enabled. 32. type [LFBS]: (0=frontend, 1=backend, 2=server, 3=socket/listener) 33. rate [.FBS]: number of sessions per second over last elapsed second 34. rate_lim [.F..]: configured limit on new sessions per second 35. rate_max [.FBS]: max number of new sessions per second 36. check_status [...S]: status of last health check, one of: UNK -> unknown INI -> initializing SOCKERR -> socket error L4OK -> check passed on layer 4, no upper layers testing enabled L4TOUT -> layer 1-4 timeout L4CON -> layer 1-4 connection problem, for example "Connection refused" (tcp rst) or "No route to host" (icmp) L6OK -> check passed on layer 6 L6TOUT -> layer 6 (SSL) timeout L6RSP -> layer 6 invalid response - protocol error L7OK -> check passed on layer 7 L7OKC -> check conditionally passed on layer 7, for example 404 with disable-on-404 L7TOUT -> layer 7 (HTTP/SMTP) timeout L7RSP -> layer 7 invalid response - protocol error L7STS -> layer 7 response error, for example HTTP 5xx 37. check_code [...S]: layer5-7 code, if available 38. check_duration [...S]: time in ms took to finish last health check 39. hrsp_1xx [.FBS]: http responses with 1xx code 40. hrsp_2xx [.FBS]: http responses with 2xx code 41. hrsp_3xx [.FBS]: http responses with 3xx code 42. hrsp_4xx [.FBS]: http responses with 4xx code 43. hrsp_5xx [.FBS]: http responses with 5xx code 44. hrsp_other [.FBS]: http responses with other codes (protocol error) 45. hanafail [...S]: failed health checks details 46. req_rate [.F..]: HTTP requests per second over last elapsed second 47. req_rate_max [.F..]: max number of HTTP requests per second observed 48. req_tot [.F..]: total number of HTTP requests received 49. cli_abrt [..BS]: number of data transfers aborted by the client 50. srv_abrt [..BS]: number of data transfers aborted by the server (inc. in eresp) 51. comp_in [.FB.]: number of HTTP response bytes fed to the compressor 52. comp_out [.FB.]: number of HTTP response bytes emitted by the compressor 53. comp_byp [.FB.]: number of bytes that bypassed the HTTP compressor (CPU/BW limit) 54. comp_rsp [.FB.]: number of HTTP responses that were compressed 55. lastsess [..BS]: number of seconds since last session assigned to server/backend 56. last_chk [...S]: last health check contents or textual error 57. last_agt [...S]: last agent check contents or textual error 58. qtime [..BS]: the average queue time in ms over the 1024 last requests 59. ctime [..BS]: the average connect time in ms over the 1024 last requests 60. rtime [..BS]: the average response time in ms over the 1024 last requests (0 for TCP) 61. ttime [..BS]: the average total session time in ms over the 1024 last requests

9.2. Unix Socket commands

The stats socket is not enabled by default. In order to enable it, it is necessary to add one line in the global section of the haproxy configuration. A second line is recommended to set a larger timeout, always appreciated when issuing commands by hand : global stats socket /var/run/haproxy.sock mode 600 level admin stats timeout 2m It is also possible to add multiple instances of the stats socket by repeating the line, and make them listen to a TCP port instead of a UNIX socket. This is never done by default because this is dangerous, but can be handy in some situations : global stats socket /var/run/haproxy.sock mode 600 level admin stats socket ipv4@192.168.0.1:9999 level admin stats timeout 2m To access the socket, an external utility such as "socat" is required. Socat is a swiss-army knife to connect anything to anything. We use it to connect terminals to the socket, or a couple of stdin/stdout pipes to it for scripts. The two main syntaxes we'll use are the following : # socat /var/run/haproxy.sock stdio # socat /var/run/haproxy.sock readline The first one is used with scripts. It is possible to send the output of a script to haproxy, and pass haproxy's output to another script. That's useful for retrieving counters or attack traces for example. The second one is only useful for issuing commands by hand. It has the benefit that the terminal is handled by the readline library which supports line editing and history, which is very convenient when issuing repeated commands (eg: watch a counter). The socket supports two operation modes : - interactive - non-interactive The non-interactive mode is the default when socat connects to the socket. In this mode, a single line may be sent. It is processed as a whole, responses are sent back, and the connection closes after the end of the response. This is the mode that scripts and monitoring tools use. It is possible to send multiple commands in this mode, they need to be delimited by a semi-colon (';'). For example : # echo "show info;show stat;show table" | socat /var/run/haproxy stdio The interactive mode displays a prompt ('>') and waits for commands to be entered on the line, then processes them, and displays the prompt again to wait for a new command. This mode is entered via the "prompt" command which must be sent on the first line in non-interactive mode. The mode is a flip switch, if "prompt" is sent in interactive mode, it is disabled and the connection closes after processing the last command of the same line. For this reason, when debugging by hand, it's quite common to start with the "prompt" command : # socat /var/run/haproxy readline prompt > show info ... > Since multiple commands may be issued at once, haproxy uses the empty line as a delimiter to mark an end of output for each command, and takes care of ensuring that no command can emit an empty line on output. A script can thus easily parse the output even when multiple commands were pipelined on a single line. It is important to understand that when multiple haproxy processes are started on the same sockets, any process may pick up the request and will output its own stats. The list of commands currently supported on the stats socket is provided below. If an unknown command is sent, haproxy displays the usage message which reminds all supported commands. Some commands support a more complex syntax, generally it will explain what part of the command is invalid when this happens. Add an entry into the acl . is the # or the returned by "show acl". This command does not verify if the entry already exists. This command cannot be used if the reference is a file also used with a map. In this case, you must use the command "add map" in place of "add acl". Add an entry into the map

to associate the value to the key . This command does not verify if the entry already exists. It is mainly used to fill a map after a clear operation. Note that if the reference

is a file and is shared with a map, this map will contain also a new pattern entry. Clear the max values of the statistics counters in each proxy (frontend & backend) and in each server. The cumulated counters are not affected. This can be used to get clean counters after an incident, without having to restart nor to clear traffic counters. This command is restricted and can only be issued on sockets configured for levels "operator" or "admin". Clear all statistics counters in each proxy (frontend & backend) and in each server. This has the same effect as restarting. This command is restricted and can only be issued on sockets configured for level "admin". </