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Reference Manual
version 1.3.15
willy tarreau
Please use "configuration.txt" from the same directory, or download
an up-to-date version from the following location :
| Abstract |
HAProxy is a TCP/HTTP reverse proxy which is particularly suited for high
availability environments. Indeed, it can :
- route HTTP requests depending on statically assigned cookies ;
- spread the load among several servers while assuring server persistence
through the use of HTTP cookies ;
- switch to backup servers in the event a main one fails ;
- accept connections to special ports dedicated to service monitoring ;
- stop accepting connections without breaking existing ones ;
- add/modify/delete HTTP headers both ways ;
- block requests matching a particular pattern ;
- hold clients to the right application server depending on application
- report detailed status as HTML pages to authenticated users from an URI
intercepted from the application.
It needs very little resource. Its event-driven architecture allows it to easily
handle thousands of simultaneous connections on hundreds of instances without
risking the system's stability.
| Start parameters |
There are only a few command line options :
-f <configuration file>
-n <high limit for the total number of simultaneous connections>
= 'maxconn' in 'global' section
-N <high limit for the per-listener number of simultaneous connections>
= 'maxconn' in 'listen' or 'default' sections
-d starts in foregreound with debugging mode enabled
-D starts in daemon mode
-q disable messages on output
-V displays messages on output even when -q or 'quiet' are specified.
-c only checks config file and exits with code 0 if no error was found, or
exits with code 1 if a syntax error was found.
-p <pidfile> asks the process to write down each of its children's
pids to this file in daemon mode.
-sf specifies a list of pids to send a FINISH signal to after startup.
-st specifies a list of pids to send a TERMINATE signal to after startup.
-s shows statistics (only if compiled in)
-l shows even more statistics (implies '-s')
-dk disables use of kqueue()
-ds disables use of speculative epoll()
-de disables use of epoll()
-dp disables use of poll()
-db disables background mode (stays in foreground, useful for debugging)
-m <megs> enforces a memory usage limit to a maximum of <megs> megabytes.
The maximal number of connections per proxy instance is used as the default
parameter for each instance for which the 'maxconn' paramter is not set in the
'listen' section.
The maximal number of total connections limits the number of connections used by
the whole process if the 'maxconn' parameter is not set in the 'global' section.
The debugging mode has the same effect as the 'debug' option in the 'global'
section. When the proxy runs in this mode, it dumps every connections,
disconnections, timestamps, and HTTP headers to stdout. This should NEVER
be used in an init script since it will prevent the system from starting up.
For debugging, the '-db' option is very useful as it temporarily disables
daemon mode and multi-process mode. The service can then be stopped by simply
pressing Ctrl-C, without having to edit the config nor run full debug.
Statistics are only available if compiled in with the 'STATTIME' option. It's
only used during code optimization phases, and will soon disappear.
The '-st' and '-sf' options are used for hot reconfiguration (see below).
| Configuration file |
The configuration file parser ignores empty lines, spaces, tabs. Anything
between a sharp ('#') not following a backslash ('\'), and the end of a line
constitutes a comment and is ignored too.
The configuration file is segmented in sections. A section begins whenever
one of these 3 keywords are encountered :
- 'global'
- 'listen'
- 'defaults'
Every parameter refer to the section beginning at the last one of these 3
1) Global parameters
Global parameters affect the whole process behaviour. They are all set in the
'global' section. There may be several 'global' sections if needed, but their
parameters will only be merged. Allowed parameters in 'global' section include
the following ones :
- log <address> <facility> [max_level]
- maxconn <number>
- uid <user id>
- gid <group id>
- user <user name>
- group <group name>
- chroot <directory>
- nbproc <number>
- daemon
- debug
- nokqueue
- nosepoll
- noepoll
- nopoll
- quiet
- pidfile <file>
- ulimit-n <number>
- stats
- tune.maxpollevents <number>
1.1) Event logging
Most events are logged : start, stop, servers going up and down, connections and
errors. Each event generates a syslog message which can be sent to up to 2
servers. The syntax is :
log <ip_address> <facility> [max_level]
Connections are logged at level "info". Services initialization and servers
going up are logged at level "notice", termination signals are logged at
"warning", and definitive service termination, as well as loss of servers are
logged at level "alert". The optional parameter <max_level> specifies above
what level messages should be sent. Level can take one of these 8 values :
emerg, alert, crit, err, warning, notice, info, debug
For backwards compatibility with versions 1.1.16 and earlier, the default level
value is "debug" if not specified.
Permitted facilities are :
kern, user, mail, daemon, auth, syslog, lpr, news,
uucp, cron, auth2, ftp, ntp, audit, alert, cron2,
local0, local1, local2, local3, local4, local5, local6, local7
According to RFC3164, messages are truncated to 1024 bytes before being emitted.
Example :
log local3
log local4 notice
1.2) limiting the number of connections
It is possible and recommended to limit the global number of per-process
connections using the 'maxconn' global keyword. Since one connection includes
both a client and a server, it means that the max number of TCP sessions will
be about the double of this number. It's important to understand this when
trying to find best values for 'ulimit -n' before starting the proxy. To
anticipate the number of sockets needed, all these parameters must be counted :
- 1 socket per incoming connection
- 1 socket per outgoing connection
- 1 socket per address/port/proxy tuple.
- 1 socket per server being health-checked
- 1 socket for all logs
In simple configurations where each proxy only listens one one address/port,
set the limit of file descriptors (ulimit -n) to
(2 * maxconn + nbproxies + nbservers + 1). Starting with versions 1.1.32/1.2.6,
it is now possible to set the limit in the configuration using the 'ulimit-n'
global keyword, provided the proxy is started as root. This puts an end to the
recurrent problem of ensuring that the system limits are adapted to the proxy
values. Note that these limits are per-process.
Example :
maxconn 32000
ulimit-n 65536
1.3) Drop of priviledges
In order to reduce the risk and consequences of attacks, in the event where a
yet non-identified vulnerability would be successfully exploited, it's possible
to lower the process priviledges and even isolate it in a riskless directory.
In the 'global' section, the 'uid' parameter sets a numerical user identifier
which the process will switch to after binding its listening sockets. The value
'0', which normally represents the super-user, here indicates that the UID must
not change during startup. It's the default behaviour. The 'gid' parameter does
the same for the group identifier. If setting an uid is not possible because of
deployment constraints, it is possible to set a user name with the 'user'
keyword followed by a valid user name. The same is true for the gid. It is
possible to specify a group name after the 'group' keyword.
It is particularly advised against use of generic accounts such as 'nobody'
because it has the same consequences as using 'root' if other services use
The 'chroot' parameter makes the process isolate itself in an empty directory
just before switching its UID. This type of isolation (chroot) can sometimes
be worked around on certain OS (Linux, Solaris), provided that the attacker
has gained 'root' priviledges and has the ability to use or create a directory.
For this reason, it's capital to use a dedicated directory and not to share one
between several services of different nature. To make isolation more resistant,
it's recommended to use an empty directory without any right, and to change the
UID of the process so that it cannot do anything there.
Note: in the event where such a vulnerability would be exploited, it's most
likely that first attempts would kill the process due to 'Segmentation Fault',
'Bus Error' or 'Illegal Instruction' signals. Eventhough it's true that
isolating the server reduces the risks of intrusion, it's sometimes useful to
find why a process dies, via the analysis of a 'core' file, although very rare
(the last bug of this sort was fixed in 1.1.9). For security reasons, most
systems disable the generation of core file when a process changes its UID. So
the two workarounds are either to start the process from a restricted user
account, which will not be able to chroot itself, or start it as root and not
change the UID. In both cases the core will be either in the start or the chroot
directories. Do not forget to allow core dumps prior to start the process :
# ulimit -c unlimited
Example :
# with uid/gid
uid 30000
gid 30000
chroot /var/chroot/haproxy
# with user/group
user haproxy
group public
chroot /var/chroot/haproxy
1.4) Startup modes
The service can start in several different modes :
- foreground / background
- quiet / normal / debug
The default mode is normal, foreground, which means that the program doesn't
return once started. NEVER EVER use this mode in a system startup script, or
the system won't boot. It needs to be started in background, so that it
returns immediately after forking. That's accomplished by the 'daemon' option
in the 'global' section, which is the equivalent of the '-D' command line
The '-db' command line argument overrides the 'daemon' and 'nbproc' global
options to make the process run in normal, foreground mode.
Moreover, certain alert messages are still sent to the standard output even
in 'daemon' mode. To make them disappear, simply add the 'quiet' option in the
'global' section. This option has no command-line equivalent.
Last, the 'debug' mode, enabled with the 'debug' option in the 'global' section,
and which is equivalent of the '-d' option, allows deep TCP/HTTP analysis, with
timestamped display of each connection, disconnection, and HTTP headers for both
ways. This mode is incompatible with 'daemon' and 'quiet' modes for obvious
1.5) Increasing the overall processing power
On multi-processor systems, it may seem to be a shame to use only one processor,
eventhough the load needed to saturate a recent processor is far above common
usage. Anyway, for very specific needs, the proxy can start several processes
between which the operating system will spread the incoming connections. The
number of processes is controlled by the 'nbproc' parameter in the 'global'
section. It defaults to 1, and obviously works only in 'daemon' mode. One
typical usage of this parameter has been to workaround the default per-process
file-descriptor limit that Solaris imposes to user processes.
Example :
nbproc 2
1.6) Helping process management
Haproxy now supports the notion of pidfile. If the '-p' command line argument,
or the 'pidfile' global option is followed with a file name, this file will be
removed, then filled with all children's pids, one per line (only in daemon
mode). This file is NOT within the chroot, which allows to work with a readonly
chroot. It will be owned by the user starting the process, and will have
permissions 0644.
Example :
nbproc 2
pidfile /var/run/
# to stop only those processes among others :
# kill $(</var/run/
# to reload a new configuration with minimal service impact and without
# breaking existing sessions :
# haproxy -f haproxy.cfg -p /var/run/ -sf $(</var/run/
1.7) Polling mechanisms
Starting from version 1.2.5, haproxy supports the poll() and epoll() polling
mechanisms. On systems where select() is limited by FD_SETSIZE (like Solaris),
poll() can be an interesting alternative. Performance tests show that Solaris'
poll() performance does not decay as fast as the numbers of sockets increase,
making it a safe solution for high loads. However, Solaris already uses poll()
to emulate select(), so as long as the number of sockets has no reason to go
higher than FD_SETSIZE, poll() should not provide any better performance. On
Linux systems with the epoll() patch (or any 2.6 version), haproxy will use
epoll() which is extremely fast and non dependant on the number of sockets.
Tests have shown constant performance from 1 to 20000 simultaneous sessions.
Version 1.3.9 introduced kqueue() for FreeBSD/OpenBSD, and speculative epoll()
which consists in trying to perform I/O before queuing the events via syscalls.
In order to optimize latency, it is now possible to limit the number of events
returned by a single call to poll. The limit is fixed to 200 by default. If a
smaller latency is seeked, it may be useful to reduce this value by using the
'tune.maxpollevents' parameter in the 'global' section. Increasing it will
slightly save CPU cycles in presence of large number of connections.
Haproxy will use kqueue() or speculative epoll() when available, then epoll(),
and will fall back to poll(), then to select(). However, if for any reason you
need to disable epoll() or poll() (eg. because of a bug or just to compare
performance), new global options have been created for this matter : 'nosepoll',
'nokqueue', 'noepoll' and 'nopoll'.
Example :
# use only select()
tune.maxpollevents 100
Note :
For the sake of configuration file portability, these options are accepted but
ignored if the poll() or epoll() mechanisms have not been enabled at compile
To make debugging easier, the '-de' runtime argument disables epoll support,
the '-dp' argument disables poll support, '-dk' disables kqueue and '-ds'
disables speculative epoll(). They are respectively equivalent to 'noepoll',
'nopoll', 'nokqueue' and 'nosepoll'.
2) Declaration of a listening service
Service sections start with the 'listen' keyword :
listen <instance_name> [ <IP_address>:<port_range>[,...] ]
- <instance_name> is the name of the instance. This name will be reported in
logs, so it is good to have it reflect the proxied service. No unicity test
is done on this name, and it's not mandatory for it to be unique, but highly
- <IP_address> is the IP address the proxy binds to. Empty address, '*' and
'' all mean that the proxy listens to all valid addresses on the
- <port_range> is either a unique port, or a port range for which the proxy will
accept connections for the IP address specified above. This range can 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 <addr:port>
couple consumes one socket (=a file descriptor), so it's easy to eat lots of
descriptors with a simple range. The <addr:port> couple must be used only once
among all instances running on a same system. Please note that attaching to
ports lower than 1024 need particular priviledges to start the program, which
are independant of the 'uid' parameter.
- the <IP_address>:<port_range> couple may be repeated indefinitely to require
the proxy to listen to other addresses and/or ports. To achieve this, simply
separate them with a coma.
Examples :
listen http_proxy :80
listen x11_proxy
listen smtp_proxy,
listen ldap_proxy :389,:663
In the event that all addresses do not fit line width, it's preferable to
detach secondary addresses on other lines with the 'bind' keyword. If this
keyword is used, it's not even necessary to specify the first address on the
'listen' line, which sometimes makes multiple configuration handling easier :
bind [ <IP_address>:<port_range>[,...] ]
Examples :
listen http_proxy
bind :80,:443
2.1) Inhibiting a service
A service may be disabled for maintenance reasons, without needing to comment
out the whole section, simply by specifying the 'disabled' keyword in the
section to be disabled :
listen smtp_proxy
Note: the 'enabled' keyword allows to enable a service which has been disabled
previously by a default configuration.
2.2) Modes of operation
A service can work in 3 different distinct modes :
- health
TCP mode
In this mode, the service relays TCP connections as soon as they're established,
towards one or several servers. No processing is done on the stream. It's only
an association of source(addr:port) -> destination(addr:port). To use this mode,
you must specify 'mode tcp' in the 'listen' section. This is the default mode.
Example :
listen smtp_proxy
mode tcp
HTTP mode
In this mode, the service relays TCP connections towards one or several servers,
when it has enough informations to decide, which normally means that all HTTP
headers have been read. Some of them may be scanned for a cookie or a pattern
matching a regex. To use this mode, specify 'mode http' in the 'listen' section.
Example :
listen http_proxy
mode http
Health-checking mode
This mode provides a way for external components to check the proxy's health.
It is meant to be used with intelligent load-balancers which can use send/expect
scripts to check for all of their servers' availability. This one simply accepts
the connection, returns the word 'OK' and closes it. If the 'option httpchk' is
set, then the reply will be 'HTTP/1.0 200 OK' with no data, so that it can be
tested from a tool which supports HTTP health-checks. To enable it, simply
specify 'health' as the working mode :
Example :
# simple response : 'OK'
listen health_check
mode health
# HTTP response : 'HTTP/1.0 200 OK'
listen http_health_check
mode health
option httpchk
2.2.1 Monitoring
Versions 1.1.32 and 1.2.6 provide a new solution to check the proxy's
availability without perturbating the service. The 'monitor-net' keyword was
created to specify a network of equipments which CANNOT use the service for
anything but health-checks. This is particularly suited to TCP proxies, because
it prevents the proxy from relaying the monitor's connection to the remote
When used with TCP, the connection is accepted then closed and nothing is
logged. This is enough for a front-end load-balancer to detect the service as
When used with HTTP, the connection is accepted, nothing is logged, the
following response is sent, then the session is closed : "HTTP/1.0 200 OK".
This is normally enough for any front-end HTTP load-balancer to detect the
service as available too, both with TCP and HTTP checks.
Proxies using the "monitor-net" keyword can remove the "option dontlognull", as
it will make them log empty connections from hosts outside the monitoring
Example :
listen tse-proxy
bind :3389,:1494,:5900 # TSE, ICA and VNC at once.
mode tcp
balance roundrobin
server tse-farm
monitor-net # L4 load-balancers on .252 and .253
When the system executing the checks is located behind a proxy, the monitor-net
keyword cannot be used because haproxy will always see the proxy's address. To
overcome this limitation, version 1.2.15 brought the 'monitor-uri' keyword. It
defines an URI which will not be forwarded nor logged, but for which haproxy
will immediately send an "HTTP/1.0 200 OK" response. This makes it possible to
check the validity of the reverse-proxy->haproxy chain with one request. It can
be used in HTTPS checks in front of an stunnel -> haproxy combination for
instance. Obviously, this keyword is only valid in HTTP mode, otherwise there
is no notion of URI. Note that the method and HTTP versions are simply ignored.
Example :
listen stunnel_backend :8080
mode http
balance roundrobin
server web1 check
server web2 check
monitor-uri /haproxy_test
2.3) Limiting the number of simultaneous connections
The 'maxconn' parameter allows a proxy to refuse connections above a certain
amount of simultaneous ones. When the limit is reached, it simply stops
listening, but the system may still be accepting them because of the back log
queue. These connections will be processed later when other ones have freed
some slots. This provides a serialization effect which helps very fragile
servers resist to high loads. See further for system limitations.
Example :
listen tiny_server
maxconn 10
2.4) Soft stop
It is possible to stop services without breaking existing connections by the
sending of the SIGUSR1 signal to the process. All services are then put into
soft-stop state, which means that they will refuse to accept new connections,
except for those which have a non-zero value in the 'grace' parameter, in which
case they will still accept connections for the specified amount of time, in
milliseconds. This makes it possible to tell a load-balancer that the service
is failing, while still doing the job during the time it needs to detect it.
Note: active connections are never killed. In the worst case, the user will have
to wait for all of them to close or to time-out, or simply kill the process
normally (SIGTERM). The default 'grace' value is '0'.
Example :
# enter soft stop after 'killall -USR1 haproxy'
# the service will still run 10 seconds after the signal
listen http_proxy
mode http
grace 10000
# this port is dedicated to a load-balancer, and must fail immediately
listen health_check
mode health
grace 0
As of version 1.2.8, a new soft-reconfiguration mechanism has been introduced.
It is now possible to "pause" all the proxies by sending a SIGTTOU signal to
the processes. This will disable the listening socket without breaking existing
connections. After that, sending a SIGTTIN signal to those processes enables
the listening sockets again. This is very useful to try to load a new
configuration or even a new version of haproxy without breaking existing
connections. If the load succeeds, then simply send a SIGUSR1 which will make
the previous proxies exit immediately once their sessions are closed ; and if
the load fails, then simply send a SIGTTIN to restore the service immediately.
Please note that the 'grace' parameter is ignored for SIGTTOU, as well as for
SIGUSR1 when the process was in the pause mode. Please also note that it would
be useful to save the pidfile before starting a new instance.
This mechanism fully exploited since 1.2.11 with the '-st' and '-sf' options
(see below).
2.4.1) Hot reconfiguration
The '-st' and '-sf' command line options are used to inform previously running
processes that a configuration is being reloaded. They will receive the SIGTTOU
signal to ask them to temporarily stop listening to the ports so that the new
process can grab them. If anything wrong happens, the new process will send
them a SIGTTIN to tell them to re-listen to the ports and continue their normal
work. Otherwise, it will either ask them to finish (-sf) their work then softly
exit, or immediately terminate (-st), breaking existing sessions. A typical use
of this allows a configuration reload without service interruption :
# haproxy -p /var/run/ -sf $(cat /var/run/
2.5) Connections expiration time
It is possible (and recommended) to configure several time-outs on TCP
connections. Three independant timers are adjustable with values specified
in milliseconds. A session will be terminated if either one of these timers
- the time we accept to wait for data from the client, or for the client to
accept data : 'clitimeout' :
# client time-out set to 2mn30.
clitimeout 150000
- the time we accept to wait for data from the server, or for the server to
accept data : 'srvtimeout' :
# server time-out set to 30s.
srvtimeout 30000
- the time we accept to wait for a connection to establish on a server :
'contimeout' :
# we give up if the connection does not complete within 4 seconds
contimeout 4000
Notes :
- 'contimeout' and 'srvtimeout' have no sense on 'health' mode servers ;
- under high loads, or with a saturated or defective network, it's possible
that some packets get lost. Since the first TCP retransmit only happens
after 3 seconds, a time-out equal to, or lower than 3 seconds cannot
compensate for a packet loss. A 4 seconds time-out seems a reasonable
minimum which will considerably reduce connection failures.
- starting with version 1.3.14, it is possible to specify timeouts in
arbitrary time units among { us, ms, s, m, h, d }. For this, the integer
value just has to be suffixed with the unit.
2.6) Attempts to reconnect
After a connection failure to a server, it is possible to retry, potentially
on another server. This is useful if health-checks are too rare and you don't
want the clients to see the failures. The number of attempts to reconnect is
set by the 'retries' paramter.
Example :
# we can retry 3 times max after a failure
retries 3
Please note that the reconnection attempt may lead to getting the connection
sent to a new server if the original one died between connection attempts.
2.7) Address of the dispatch server (deprecated)
The server which will be sent all new connections is defined by the 'dispatch'
parameter, in the form <address>:<port>. It generally is dedicated to unknown
connections and will assign them a cookie, in case of HTTP persistence mode,
or simply is a single server in case of generic TCP proxy. This old mode is only
provided for backwards compatibility, but doesn't allow to check remote servers
state, and has a rather limited usage. All new setups should switch to 'balance'
mode. The principle of the dispatcher is to be able to perform the load
balancing itself, but work only on new clients so that the server doesn't need
to be a big machine.
Example :
# all new connections go there
Note :
This parameter has no sense for 'health' servers, and is incompatible with
'balance' mode.
2.8) Outgoing source address
It is often necessary to bind to a particular address when connecting to some
remote hosts. This is done via the 'source' parameter which is a per-proxy
parameter. A newer version may allow to fix different sources to reach different
servers. The syntax is 'source <address>[:<port>]', where <address> is a valid
local address (or '' or '*' or empty to let the system choose), and
<port> is an optional parameter allowing the user to force the source port for
very specific needs. If the port is not specified or is '0', the system will
choose a free port. Note that as of version 1.1.18, the servers health checks
are also performed from the same source.
Examples :
listen http_proxy *:80
# all connections take as source address
listen rlogin_proxy *:513
# use address and the reserved port 900 (needs to be root)
2.9) Setting the cookie name
In HTTP mode, it is possible to look for a particular cookie which will contain
a server identifier which should handle the connection. The cookie name is set
via the 'cookie' parameter.
Example :
listen http_proxy :80
mode http
It is possible to change the cookie behaviour to get a smarter persistence,
depending on applications. It is notably possible to delete or modify a cookie
emitted by a server, insert a cookie identifying the server in an HTTP response
and even add a header to tell upstream caches not to cache this response.
Examples :
To remove the cookie for direct accesses (ie when the server matches the one
which was specified in the client cookie) :
cookie SERVERID indirect
To replace the cookie value with the one assigned to the server if any (no
cookie will be created if the server does not provide one, nor if the
configuration does not provide one). This lets the application put the cookie
exactly on certain pages (eg: successful authentication) :
cookie SERVERID rewrite
To create a new cookie and assign the server identifier to it (in this case, all
servers should be associated with a valid cookie, since no cookie will simply
delete the cookie from the client's browser) :
cookie SERVERID insert
To reuse an existing application cookie and prefix it with the server's
identifier, and remove it in the request, use the 'prefix' option. This allows
to insert a haproxy in front of an application without risking to break clients
which does not support more than one cookie :
cookie JSESSIONID prefix
To insert a cookie and ensure that no upstream cache will store it, add the
'nocache' option :
cookie SERVERID insert nocache
To insert a cookie only after a POST request, add 'postonly' after 'insert'.
This has the advantage that there's no risk of caching, and that all pages
seen before the POST one can still be cached :
cookie SERVERID insert postonly
Notes :
- it is possible to combine 'insert' with 'indirect' or 'rewrite' to adapt to
applications which already generate the cookie with an invalid content.
- in the case where 'insert' and 'indirect' are both specified, the cookie is
never transmitted to the server, since it wouldn't understand it. This is the
most application-transparent mode.
- it is particularly recommended to use 'nocache' in 'insert' mode if any
upstream HTTP/1.0 cache is susceptible to cache the result, because this may
lead to many clients going to the same server, or even worse, some clients
having their server changed while retrieving a page from the cache.
- the 'prefix' mode normally does not need 'indirect', 'nocache', nor
'postonly', because just as in the 'rewrite' mode, it relies on the
application to know when a cookie can be emitted. However, since it has to
fix the cookie name in every subsequent requests, you must ensure that the
proxy will be used without any "HTTP keep-alive". Use option "httpclose" if
- when the application is well known and controlled, the best method is to
only add the persistence cookie on a POST form because it's up to the
application to select which page it wants the upstream servers to cache. In
this case, you would use 'insert postonly indirect'.
2.10) Associating a cookie value with a server
In HTTP mode, it's possible to associate a cookie value to each server. This
was initially used in combination with 'dispatch' mode to handle direct accesses
but it is now the standard way of doing the load balancing. The syntax is :
server <identifier> <address>:<port> cookie <value>
- <identifier> is any name which can be used to identify the server in the logs.
- <address>:<port> specifies where the server is bound.
- <value> is the value to put in or to read from the cookie.
Example : the 'SERVERID' cookie can be either 'server01' or 'server02'
listen http_proxy :80
mode http
server web1 cookie server01
server web2 cookie server02
Warning : the syntax has changed since version 1.0 !
2.11) Application Cookies
Since 1.2.4 it is possible to catch the cookie that comes from an
application server in order to apply "application session stickyness".
The server's response is searched for 'appsession' cookie, the first
'len' bytes are used for matching and it is stored for a period of
The syntax is:
appsession <session_cookie> len <match_length> timeout <holdtime>
- <session_cookie> is the cookie, the server uses for it's session-handling
- <match_length> how many bytes/characters should be used for matching equal
- <holdtime> after this inactivaty time, in ms, the cookie will be deleted
from the sessionstore
- starting with version 1.3.14, it is possible to specify timeouts in
arbitrary time units among { us, ms, s, m, h, d }. For this, the integer
value just has to be prefixed with the unit.
The appsession is only per 'listen' section possible.
Example :
listen http_lb1
mode http
capture request header Cookie len 200
# Havind a ServerID cookie on the client allows him to reach
# the right server even after expiration of the appsession.
cookie ServerID insert nocache indirect
# Will memorize 52 bytes of the cookie 'JSESSIONID' and keep them
# for 3 hours. It will match it in the cookie and the URL field.
appsession JSESSIONID len 52 timeout 3h
server first1 check inter 3000 cookie first
server secon1 check inter 3000 cookie secon
server first1 check inter 3000 cookie first
server secon2 check inter 3000 cookie secon
option httpchk GET /test.jsp
3) Autonomous load balancer
The proxy can perform the load-balancing itself, both in TCP and in HTTP modes.
This is the most interesting mode which obsoletes the old 'dispatch' mode
described above. It has advantages such as server health monitoring, multiple
port binding and port mapping. To use this mode, the 'balance' keyword is used,
followed by the selected algorithm. Up to version 1.2.11, only 'roundrobin' was
available, which is also the default value if unspecified. Starting with
version 1.2.12, a new 'source' keyword appeared. A new 'uri' keyword was added
in version 1.3.10. In this mode, there will be no dispatch address, but the
proxy needs at least one server.
Example : same as the last one, with internal load balancer
listen http_proxy :80
mode http
balance roundrobin
server web1 cookie server01
server web2 cookie server02
Since version 1.1.22, it is possible to automatically determine on which port
the server will get the connection, depending on the port the client connected
to. Indeed, there now are 4 possible combinations for the server's <port> field:
- unspecified or '0' :
the connection will be sent to the same port as the one on which the proxy
received the client connection itself.
- numerical value (the only one supported in versions earlier than 1.1.22) :
the connection will always be sent to the specified port.
- '+' followed by a numerical value :
the connection will be sent to the same port as the one on which the proxy
received the connection, plus this value.
- '-' followed by a numerical value :
the connection will be sent to the same port as the one on which the proxy
received the connection, minus this value.
Examples :
# same as previous example
listen http_proxy :80
mode http
balance roundrobin
server web1 cookie server01
server web2 cookie server02
# simultaneous relaying of ports 80, 81 and 8080-8089
listen http_proxy :80,:81,:8080-8089
mode http
balance roundrobin
server web1 cookie server01
server web2 cookie server02
# relaying of TCP ports 25, 389 and 663 to ports 1025, 1389 and 1663
listen http_proxy :25,:389,:663
mode tcp
balance roundrobin
server srv1
server srv2
As previously stated, version 1.2.12 brought the 'source' keyword. When this
keyword is used, the client's IP address is hashed and evenly distributed among
the available servers so that a same source IP will always go to the same
server as long as there are no change in the number of available servers. This
can be used for instance to bind HTTP and HTTPS to the same server. It can also
be used to improve stickyness when one part of the client population does not
accept cookies. In this case, only those ones will be perturbated should a
server fail.
NOTE: It is important to consider the fact that many clients surf the net
through proxy farms which assign different IP addresses for each
request. Others use dialup connections with a different IP at each
connection. Thus, the 'source' parameter should be used with extreme
Examples :
# make a same IP go to the same server whatever the service
listen http_proxy
bind :80,:443
mode http
balance source
server web1
server web2
# try to improve client-server binding by using both source IP and cookie :
listen http_proxy :80
mode http
balance source
server web1 cookie server01
server web2 cookie server02
As indicated above, the 'uri' keyword was introduced in version 1.3.10. It is
useful when load-balancing between reverse proxy-caches, because it will hash
the URI and use the hash result to select a server, thus optimizing the hit
rate on the caches, because the same URI will always reach the same cache. This
keyword is only allowed in HTTP mode.
Example :
# Always send a given URI to the same server
listen http_proxy
bind :3128
mode http
balance uri
server squid1
server squid2
Version 1.3.14 introduced the "balance url_param" method. It consists in
relying on a parameter passed in the URL to perform a hash. This is mostly
useful for applications which do not have strict persistence requirements,
but for which it still provides a performance boost due to local caching.
Some of these applications may not be able to use a cookie for whatever reason,
but may be able to look for a parameter passed in the URL. If the parameter is
missing from the URL, then the 'round robin' method applies.
A modifier may be added to specify that parameters in POST requests may be
found in the messsage body if the URL lacks a '?' separator character.
A wait limit may also be applied, if no limit is requested then
the default value is 48 octets, the minimum is 3. HAProxy may wait, until 48
octets are received. If Content-Length is missing, or zero it need not
wait for more data then the client promissed to send. When Content-Length is
present, and more than <max_wait>; then waiting is limited and it is assumed this
will be enough data to search for the presence of a parameter. If
Transfer-Encoding: chunked is used (unlikely), then the length of the first chunk
is the maximum number of bytes to wait for.
balance url_param <param> [check_post [<max_wait>]]
Caveats for using the check_post extension:
- all POST requests are eligable 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)
Limitations on inspecting the entity body of a POST:
- 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. Scaning 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.
Example :
# Hash the "basket_id" argument from the URL to determine the server
listen http_proxy
bind :3128
mode http
balance url_param basket_id
server ebiz1
server ebiz2
3.1) Server monitoring
It is possible to check the servers status by trying to establish TCP
connections or even sending HTTP requests to them. A server which fails to
reply to health checks as expected will not be used by the load balancing
algorithms. To enable monitoring, add the 'check' keyword on a server line.
It is possible to specify the interval between tests (in milliseconds) with
the 'inter' parameter, the number of failures supported before declaring that
the server has fallen down with the 'fall' parameter, and the number of valid
checks needed for the server to fully get up with the 'rise' parameter. Since
version 1.1.22, it is also possible to send checks to a different port
(mandatory when none is specified) with the 'port' parameter. The default
values are the following ones :
- inter : 2000
- rise : 2
- fall : 3
- port : default server port
- addr : specific address for the test (default = address server)
The default mode consists in establishing TCP connections only. But in certain
types of application failures, it is often that the server continues to accept
connections because the system does it itself while the application is running
an endless loop, or is completely stuck. So in version 1.1.16 were introduced
HTTP health checks which only performed simple lightweight requests and analysed
the response. Now, as of version 1.1.23, it is possible to change the HTTP
method, the URI, and the HTTP version string (which even allows to send headers
with a dirty trick). To enable HTTP health-checks, use 'option httpchk'.
By default, requests use the 'OPTIONS' method because it's very light and easy
to filter from logs, and does it on '/'. Only HTTP responses 2xx and 3xx are
considered valid ones, and only if they come before the time to send a new
request is reached ('inter' parameter). If some servers block this type of
request, 3 other forms help to forge a request :
- option httpchk -> OPTIONS / HTTP/1.0
- option httpchk URI -> OPTIONS <URI> HTTP/1.0
- option httpchk METH URI -> <METH> <URI> HTTP/1.0
- option httpchk METH URI VER -> <METH> <URI> <VER>
Some people are using HAProxy to relay various TCP-based protocols such as
HTTPS, SMTP or LDAP, with the most common one being HTTPS. One problem commonly
encountered in data centers is the need to forward the traffic to far remote
servers while providing server fail-over. Often, TCP-only checks are not enough
because intermediate firewalls, load balancers or proxies might acknowledge the
connection before it reaches the real server. The only solution to this problem
is to send application-level health checks. Since the demand for HTTPS checks
is high, it has been implemented in 1.2.15 based on SSLv3 Client Hello packets.
To enable it, use 'option ssl-hello-chk'. It will send SSL CLIENT HELLO packets
to the servers, announcing support for most common cipher suites. If the server
responds what looks like a SERVER HELLO or an ALERT (refuses the ciphers) then
the response is considered as valid. Note that Apache does not generate a log
when it receives only an HELLO message, which makes this type of message
perfectly suit this need.
Version 1.3.10 introduced the SMTP health check. By default, it sends
"HELO localhost" to the servers, and waits for the 250 message. Note that it
can also send a specific request :
- option smtpchk -> sends "HELO localhost"
- option smtpchk EHLO -> sends this ESMTP greeting
See examples below.
Since version 1.1.17, it is possible to specify backup servers. These servers
are only sollicited when no other server is available. This may only be useful
to serve a maintenance page, or define one active and one backup server (seldom
used in TCP mode). To make a server a backup one, simply add the 'backup' option
on its line. These servers also support cookies, so if a cookie is specified for
a backup server, clients assigned to this server will stick to it even when the
other ones come back. Conversely, if no cookie is assigned to such a server,
the clients will get their cookies removed (empty cookie = removal), and will
be balanced against other servers once they come back. Please note that there
is no load-balancing among backup servers by default. If there are several
backup servers, the second one will only be used when the first one dies, and
so on. To force load-balancing between backup servers, specify the 'allbackups'
Since version 1.1.22, it is possible to send health checks to a different port
than the service. It is mainly needed in setups where the server does not have
any predefined port, for instance when the port is deduced from the listening
port. For this, use the 'port' parameter followed by the port number which must
respond to health checks. It is also possible to send health checks to a
different address than the service. It makes it easier to use a dedicated check
daemon on the servers, for instance, check return contents and stop several
farms at once in the event of an error anywhere.
Since version 1.1.17, it is also possible to visually check the status of all
servers at once. For this, you just have to send a SIGHUP signal to the proxy.
The servers status will be dumped into the logs at the 'notice' level, as well
as on <stderr> if not closed. For this reason, it's always a good idea to have
one local log server at the 'notice' level.
Since version 1.1.28 and 1.2.1, if an instance loses all its servers, an
emergency message will be sent in the logs to inform the administator that an
immediate action must be taken.
Since version 1.1.30 and 1.2.3, several servers can share the same cookie
value. This is particularly useful in backup mode, to select alternate paths
for a given server for example, to provide soft-stop, or to direct the clients
to a temporary page during an application restart. The principle is that when
a server is dead, the proxy will first look for another server which shares the
same cookie value for every client which presents the cookie. If there is no
standard server for this cookie, it will then look for a backup server which
shares the same name. Please consult the architecture guide for more information.
Examples :
# same setup as in paragraph 3) with TCP monitoring
listen http_proxy
mode http
balance roundrobin
server web1 cookie server01 check
server web2 cookie server02 check inter 500 rise 1 fall 2
# same with HTTP monitoring via 'OPTIONS / HTTP/1.0'
listen http_proxy
mode http
balance roundrobin
option httpchk
server web1 cookie server01 check
server web2 cookie server02 check inter 500 rise 1 fall 2
# same with HTTP monitoring via 'OPTIONS /index.html HTTP/1.0'
listen http_proxy
mode http
balance roundrobin
option httpchk /index.html
server web1 cookie server01 check
server web2 cookie server02 check inter 500 rise 1 fall 2
# same with HTTP monitoring via 'HEAD /index.jsp? HTTP/1.1\r\nHost: www'
listen http_proxy
mode http
balance roundrobin
option httpchk HEAD /index.jsp? HTTP/1.1\r\nHost:\ www
server web1 cookie server01 check
server web2 cookie server02 check inter 500 rise 1 fall 2
# Load-balancing with 'prefixed cookie' persistence, and soft-stop using an
# alternate port 81 on the server for health-checks.
listen http_proxy
mode http
cookie JSESSIONID prefix
balance roundrobin
option httpchk HEAD /index.jsp? HTTP/1.1\r\nHost:\ www
server web1-norm cookie s1 check port 81
server web2-norm cookie s2 check port 81
server web1-stop cookie s1 check port 80 backup
server web2-stop cookie s2 check port 80 backup
# automatic insertion of a cookie in the server's response, and automatic
# deletion of the cookie in the client request, while asking upstream caches
# not to cache replies.
listen web_appl
mode http
cookie SERVERID insert nocache indirect
balance roundrobin
server web1 cookie server01 check
server web2 cookie server02 check
# same with off-site application backup and local error pages server
listen web_appl
mode http
cookie SERVERID insert nocache indirect
balance roundrobin
server web1 cookie server01 check
server web2 cookie server02 check
server web-backup cookie server03 check backup
server web-excuse check backup
# SMTP+TLS relaying with health-checks and backup servers
listen http_proxy :25,:587
mode tcp
balance roundrobin
server srv1 check port 25 inter 30000 rise 1 fall 2
server srv2 backup
# HTTPS relaying with health-checks and backup servers
listen http_proxy :443
mode tcp
option ssl-hello-chk
balance roundrobin
server srv1 check inter 30000 rise 1 fall 2
server srv2 backup
# Load-balancing using a backup pool (requires haproxy 1.2.9)
listen http_proxy
mode http
balance roundrobin
option httpchk
server inst1 cookie s1 check
server inst2 cookie s2 check
server inst3 cookie s3 check
server back1 check backup
server back2 check backup
option allbackups # all backups will be used
3.2) Redistribute connections in case of failure
In HTTP mode, if a server designated by a cookie does not respond, the clients
may definitely stick to it because they cannot flush the cookie, so they will
not be able to access the service anymore. Specifying 'redispatch' will allow
the proxy to break their persistence and redistribute them to working servers.
Example :
listen http_proxy
mode http
server web1 cookie server01
server web2 cookie server02
redispatch # send back to dispatch in case of connection failure
Up to, and including version 1.1.16, this parameter only applied to connection
failures. Since version 1.1.17, it also applies to servers which have been
detected as failed by the health check mechanism. Indeed, a server may be broken
but still accepting connections, which would not solve every case. But it is
possible to conserve the old behaviour, that is, make a client insist on trying
to connect to a server even if it is said to be down, by setting the 'persist'
option :
listen http_proxy
mode http
option persist
server web1 cookie server01
server web2 cookie server02
redispatch # send back to dispatch in case of connection failure
3.3) Assigning different weights to servers
Sometimes you will need to bring new servers to increase your server farm's
capacity, but the new server will be either smaller (emergency use of anything
that fits) or bigger (when investing in new hardware). For this reason, it
might be wise to be able to send more clients to biggest servers. Till version
1.2.11, it was necessary to replicate the same server multiple times in the
configuration. Starting with 1.2.12, the 'weight' option is available. HAProxy
then computes the most homogenous possible map of servers based on their
weights so that the load gets distributed as smoothly as possible among them.
The weight, between 1 and 256, should reflect one server's capacity relative to
others. Weight 1 represents the lowest frequency and 256 the highest. This way,
if a server fails, the remaining capacities are still respected.
Example :
# fair distribution among two opterons and one old pentium3
listen web_appl
mode http
cookie SERVERID insert nocache indirect
balance roundrobin
server pentium3-800 cookie server01 weight 8 check
server opteron-2.0G cookie server02 weight 20 check
server opteron-2.4G cookie server03 weight 24 check
server web-backup1 cookie server04 check backup
server web-excuse check backup
Notes :
- if unspecified, the default weight is 1
- the weight does not impact health checks, so it is cleaner to use weights
than replicating the same server several times
- weights also work on backup servers if the 'allbackups' option is used
- the weights also apply to the source address load balancing
('balance source').
- whatever the weights, the first server will always be assigned first. This
is helpful for troubleshooting.
- for the purists, the map calculation algorithm gives precedence to first
server, so the map is the most uniform when servers are declared in
ascending order relative to their weights.
The load distribution will follow exactly this sequence :
Request| 1 1 1 1
number | 1 2 3 4 5 6 7 8 9 0 1 2 3
p3-800 | X . . . . . . X . . . . .
opt-20 | . X . X . X . . . X . X .
opt-24 | . . X . X . X . X . X . X
3.4) Limiting the number of concurrent sessions on each server
Some pre-forked servers such as Apache suffer from too many concurrent
sessions, because it's very expensive to run hundreds or thousands of
processes on one system. One solution is to increase the number of servers
and load-balance between them, but it is a problem when the only goal is
to resist to short surges.
To solve this problem, a new feature was implemented in HAProxy 1.2.13.
It's a per-server 'maxconn', associated with a per-server and a per-proxy
queue. This transforms haproxy into a request buffer between the thousands of
clients and the few servers. On many circumstances, lowering the maxconn value
will increase the server's performance and decrease the overall response times
because the servers will be less congested.
When a request tries to reach any server, the first non-saturated server is
used, respective to the load balancing algorithm. If all servers are saturated,
then the request gets queued into the instance's global queue. It will be
dequeued once a server will have freed a session and all previously queued
requests have been processed.
If a request references a particular server (eg: source hashing, or persistence
cookie), and if this server is full, then the request will be queued into the
server's dedicated queue. This queue has higher priority than the global queue,
so it's easier for already registered users to enter the site than for new
For this, the logs have been enhanced to show the number of sessions per
server, the request's position in the queue and the time spent in the queue.
This helps doing capacity planning. See the 'logs' section below for more info.
Example :
# be nice with P3 which only has 256 MB of RAM.
listen web_appl
maxconn 10000
mode http
cookie SERVERID insert nocache indirect
balance roundrobin
server pentium3-800 cookie s1 weight 8 maxconn 100 check
server opteron-2.0G cookie s2 weight 20 maxconn 300 check
server opteron-2.4G cookie s3 weight 24 maxconn 300 check
server web-backup1 cookie s4 check maxconn 200 backup
server web-excuse check backup
This was so much efficient at reducing the server's response time that some
users wanted to use low values to improve their server's performance. However,
they were not able anymore to handle very large loads because it was not
possible anymore to saturate the servers. For this reason, version 1.2.14 has
brought dynamic limitation with the addition of the parameter 'minconn'. When
this parameter is set along with maxconn, it will enable dynamic limitation
based on the instance's load. The maximum number of concurrent sessions on a
server will be proportionnal to the number of sessions on the instance relative
to its maxconn. A minimum of <minconn> will be allowed whatever the load. This
will ensure that servers will perform at their best level under normal loads,
while still handling surges when needed. The dynamic limit is computed like
this :
srv.dyn_limit = max(srv.minconn, srv.maxconn * inst.sess / inst.maxconn)
Example :
# be nice with P3 which only has 256 MB of RAM.
listen web_appl
maxconn 10000
mode http
cookie SERVERID insert nocache indirect
balance roundrobin
server pentium3-800 cookie s1 weight 8 minconn 10 maxconn 100 check
server opteron-2.0G cookie s2 weight 20 minconn 30 maxconn 300 check
server opteron-2.4G cookie s3 weight 24 minconn 30 maxconn 300 check
server web-backup1 cookie s4 check maxconn 200 backup
server web-excuse check backup
In the example above, the server 'pentium3-800' will receive at most 100
simultaneous sessions when the proxy instance will reach 10000 sessions, and
will receive only 10 simultaneous sessions when the proxy will be under 1000
It is possible to limit server queue length in order to rebalance excess
sessions between less busy application servers IF session affinity isn't
hard functional requirement (for example it just gives huge performance boost
by keeping server-local caches hot and compact). 'maxqueue' option sets a
queue limit on a server, as in example below:
... (just the same as in example above)
server pentium3-800 cookie s1 weight 8 minconn 10 maxconn 100 check maxqueue 50
server opteron-2.0G cookie s2 weight 20 minconn 30 maxconn 300 check maxqueue 200
server opteron-2.4G cookie s3 weight 24 minconn 30 maxconn 300 check
Absence of 'maxqueue' option means unlimited queue. When queue gets filled
up to 'maxqueue' client session is moved from server-local queue to a global
Notes :
- The requests will not stay indefinitely in the queue, they follow the
'contimeout' parameter, and if a request cannot be dequeued within this
timeout because the server is saturated or because the queue is filled,
the session will expire with a 503 error.
- if only <minconn> is specified, it has the same effect as <maxconn>
- setting too low values for maxconn might improve performance but might also
allow slow users to block access to the server for other users.
3.5) Dropping aborted requests
In presence of very high loads, the servers will take some time to respond. The
per-proxy's connection queue will inflate, and the response time will increase
respective to the size of the queue times the average per-session response
time. When clients will wait for more than a few seconds, they will often hit
the 'STOP' button on their browser, leaving a useless request in the queue, and
slowing down other users.
As there is no way to distinguish between a full STOP and a simple
shutdown(SHUT_WR) on the client side, HTTP agents should be conservative and
consider that the client might only have closed its output channel while
waiting for the response. However, this introduces risks of congestion when
lots of users do the same, and is completely useless nowadays because probably
no client at all will close the session while waiting for the response. Some
HTTP agents support this (Squid, Apache, HAProxy), and others do not (TUX, most
hardware-based load balancers). So the probability for a closed input channel
to represent a user hitting the 'STOP' button is close to 100%, and it is very
tempting to be able to abort the session early without polluting the servers.
For this reason, a new option "abortonclose" was introduced in version 1.2.14.
By default (without the option) the behaviour is HTTP-compliant. But when the
option is specified, a session with an incoming channel closed will be aborted
if it's still possible, which means that it's either waiting for a connect() to
establish or it is queued waiting for a connection slot. This considerably
reduces the queue size and the load on saturated servers when users are tempted
to click on STOP, which in turn reduces the response time for other users.
Example :
listen web_appl
maxconn 10000
mode http
cookie SERVERID insert nocache indirect
balance roundrobin
server web1 cookie s1 weight 10 maxconn 100 check
server web2 cookie s2 weight 10 maxconn 100 check
server web3 cookie s3 weight 10 maxconn 100 check
server bck1 cookie s4 check maxconn 200 backup
option abortonclose
4) Additionnal features
Other features are available. They are transparent mode, event logging, header
rewriting/filtering, and the status as an HTML page.
4.1) Network features
4.1.1) Transparent mode
In HTTP mode, the 'transparent' keyword allows to intercept sessions which are
routed through the system hosting the proxy. This mode was implemented as a
replacement for the 'dispatch' mode, since connections without cookie will be
sent to the original address while known cookies will be sent to the servers.
This mode implies that the system can redirect sessions to a local port.
Example :
listen http_proxy
mode http
server server01
server server02
# iptables -t nat -A PREROUTING -i eth0 -p tcp -d \
--dport 80 -j REDIRECT --to-ports 65000
Note :
If the port is left unspecified on the server, the port the client connected to
will be used. This allows to relay a full port range without using transparent
mode nor thousands of file descriptors, provided that the system can redirect
sessions to local ports.
Example :
# redirect all ports to local port 65000, then forward to the server on the
# original port.
listen http_proxy
mode tcp
server server01 check port 60000
server server02 check port 60000
# iptables -t nat -A PREROUTING -i eth0 -p tcp -d \
-j REDIRECT --to-ports 65000
4.1.2) Per-server source address binding
As of versions 1.1.30 and 1.2.3, it is possible to specify a particular source
to reach each server. This is useful when reaching backup servers from a
different LAN, or to use an alternate path to reach the same server. It is also
usable to provide source load-balancing for outgoing connections. Obviously,
the same source address is used to send health-checks.
Example :
# use a particular source to reach both servers
listen http_proxy
mode http
balance roundrobin
server server01 source
server server02 source
Example :
# use a particular source to reach each servers
listen http_proxy
mode http
balance roundrobin
server server01 source
server server02 source
Example :
# provide source load-balancing to reach the same proxy through 2 WAN links
listen http_proxy
mode http
balance roundrobin
server remote-proxy-way1 source
server remote-proxy-way2 source
Example :
# force a TCP connection to bind to a specific port
listen http_proxy
mode tcp
balance roundrobin
server srv1 source
server srv2 source
4.1.3) TCP keep-alive
With version 1.2.7, it becomes possible to enable TCP keep-alives on both the
client and server sides. This makes it possible to prevent long sessions from
expiring on external layer 4 components such as firewalls and load-balancers.
It also allows the system to terminate dead sessions when no timeout has been
set (not recommanded). The proxy cannot set the keep-alive probes intervals nor
maximal count, consult your operating system manual for this. There are 3
options to enable TCP keep-alive :
option tcpka # enables keep-alive both on client and server side
option clitcpka # enables keep-alive only on client side
option srvtcpka # enables keep-alive only on server side
4.1.4) TCP lingering
It is possible to disable the system's lingering of data unacked by the client
at the end of a session. This is sometimes required when haproxy is used as a
front-end with lots of unreliable clients, and you observe thousands of sockets
in the FIN_WAIT state on the machine. This may be used in a frontend to affect
the client-side connection, as well as in a backend for the server-side
connection :
option nolinger # disables data lingering
4.2) Event logging
HAProxy's strength certainly lies in 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 log information
include client ports, TCP/HTTP state timers, precise session state at
termination and precise termination cause, information about decisions to
direct trafic to a server, and of course the ability to capture arbitrary
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-listener system and internal errors (lack of resource, bugs, ...)
- per-listener external troubles (servers up/down, max connections)
- per-listener 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
4.2.1) Log levels
TCP and HTTP connections can be logged with informations such as date, time,
source IP address, destination address, connection duration, response times,
HTTP request, the HTTP return code, number of bytes transmitted, the conditions
in which the session ended, and even exchanged cookies values, to track a
particular user's problems for example. All messages are sent to up to two
syslog servers. Consult section 1.1 for more info about log facilities. The
syntax follows :
log <address_1> <facility_1> [max_level_1]
log <address_2> <facility_2> [max_level_2]
log global
Note :
The particular syntax 'log global' means that the same log configuration as the
'global' section will be used.
Example :
listen http_proxy
mode http
log local3
log local4
4.2.2) Log format
By default, connections are logged at the TCP level, as soon as the session
establishes between the client and the proxy. By enabling the 'tcplog' option,
the proxy will wait until the session ends to generate an enhanced log
containing more information such as session duration and its state during the
disconnection. The number of remaining session after disconnection is also
indicated (for the server, the listener, and the process).
Example of TCP logging :
listen relais-tcp
mode tcp
option tcplog
log local3
>>> haproxy[18989]: [15/Oct/2003:15:24:28] relais-tcp Srv1 0/0/5007 0 -- 1/1/1 0/0
Field Format Example
1 process_name '[' pid ']:' haproxy[18989]:
2 client_ip ':' client_port
3 '[' date ']' [15/Oct/2003:15:24:28]
4 listener_name relais-tcp
5 server_name Srv1
6 queue_time '/' connect_time '/' total_time 0/0/5007
7 bytes_read 0
8 termination_state --
9 srv_conn '/' listener_conn '/' process_conn 1/1/1
10 position in srv_queue / listener_queue 0/0
Another option, 'httplog', provides more detailed information about HTTP
contents, such as the request and some cookies. In the event where an external
component would establish frequent connections to check the service, logs may be
full of useless lines. So it is possible not to log any session which didn't
transfer any data, by the setting of the 'dontlognull' option. This only has
effect on sessions which are established then closed.
Example of HTTP logging :
listen http_proxy
mode http
option httplog
option dontlognull
log local3
>>> haproxy[674]: [15/Oct/2003:08:31:57] relais-http Srv1 9/0/7/147/723 200 243 - - ---- 34/34/15/8/3 0/0 "HEAD / HTTP/1.0"
More complete example
haproxy[18989]: [15/Oct/2003:15:26:31] relais-http Srv1 3183/-1/-1/-1/11215 503 0 - - SC-- 205/202/150/137/+4 0/0 {|Mozilla} {} "HEAD / HTTP/1.0"
Field Format Example
1 process_name '[' pid ']:' haproxy[18989]:
2 client_ip ':' client_port
3 '[' date ']' [15/Oct/2003:15:26:31]
4 listener_name relais-http
5 server_name Srv1
6 Tq '/' Tw '/' Tc '/' Tr '/' Tt 3183/-1/-1/-1/11215
7 HTTP_return_code 503
8 bytes_read 0
9 captured_request_cookie -
10 captured_response_cookie -
11 termination_state SC--
12 actconn '/' feconn '/' beconn '/' srv_conn '/' retries 205/202/150/137/+4
13 position in srv_queue / listener_queue 0/0
14 '{' captured_request_headers '}' {|Mozilla}
15 '{' captured_response_headers '}' {}
16 '"' HTTP_request '"' "HEAD / HTTP/1.0"
Note for log parsers: the URI is ALWAYS the end of the line starting with the
first double quote '"'.
The retries count may have additional '+' sign means that the connection had been
redispatched from one server to another shortly before retries limit (retries 4
in above example) was depleted.
The problem when logging at end of connection is that you have no clue about
what is happening during very long sessions. To workaround this problem, a
new option 'logasap' has been introduced in 1.1.28/1.2.1. When specified, the
proxy will 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
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 bigger.
Example :
listen http_proxy
mode http
option httplog
option dontlognull
option logasap
log local3
>>> haproxy[674]: [15/Oct/2003:08:32:17] relais-http Srv1 9/10/7/14/+30 200 +243 - - ---- 3/1/1/1/0 1/0 "GET /image.iso HTTP/1.0"
4.2.3) Timing events
Timers provide a great help in trouble shooting network problems. All values
are reported in milliseconds (ms). In HTTP mode, four control points are
reported under the form 'Tq/Tw/Tc/Tr/Tt' :
- Tq: total time to get the client request.
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.
- Tw: total time spent in the queues waiting for a connection slot. It
accounts for listener's queue as well as the server's queue, and depends
on the queue size, and the time needed for the server to complete previous
sessions. The value '-1' means that the request was killed before reaching
the queue.
- 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, or between the TCP SYN packet
and the matching SYN/ACK in return. The value '-1' means that the
connection never established.
- Tr: server response time. It's the time elapsed between the moment the
TCP connection was established to the server and the moment it send its
complete response header. It purely shows its request processing time,
without the network overhead due to the data transmission. The value '-1'
means that the last the response header (empty line) was never seen.
- 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 substracting other timers when valid :
Td = Tt - (Tq + Tw + Tc + Tr)
Timers with '-1' values have to be excluded from this equation.
In TCP mode ('option tcplog'), only Tw, Tc and Tt are reported.
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 packets lost
due to network problems (wires or negociation). Moreover, if <Tt> is close to
a timeout value specified in the configuration, it often means that a session
has been aborted on time-out.
Most common cases :
- If Tq is close to 3000, a packet has probably been lost between the client
and the proxy.
- If Tc is close to 3000, a packet has probably been lost between the server
and the proxy during the server connection phase. This one should always be
very low (less than a few tens).
- 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 often slightly higher than a time-out, it's often because the
client and the server use HTTP keep-alive and the session is maintained
after the response ends. Se further for how to disable HTTP keep-alive.
Other cases ('xx' means any value to be ignored) :
-1/xx/xx/xx/Tt: the client was not able to send its complete request in time,
or that it aborted it too early.
Tq/-1/xx/xx/Tt: it was not possible to process the request, maybe because
servers were out of order.
Tq/Tw/-1/xx/Tt: the connection could not establish on the server. Either it
refused it or it timed out after Tt-(Tq+Tw) ms.
Tq/Tw/Tc/-1/Tt: the server has accepted the connection but did not return a
complete response in time, or it closed its connexion
unexpectedly, after Tt-(Tq+Tw+Tc) ms.
4.2.4) Session state at disconnection
TCP and HTTP logs provide a session completion indicator in the
<termination_state> field, just before the number of active
connections. It is 2-characters long in TCP, and 4-characters long in
HTTP, 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,
or because of a security check which detected and blocked a
dangerous error in server response which might have caused
information leak (eg: cacheable cookie).
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.
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 is a bug.
c : the client-side time-out expired first.
s : the server-side time-out expired first.
- : normal session completion.
- on the second character, the TCP/HTTP session state when it was closed :
R : waiting for complete REQUEST from the client (HTTP only). Nothing
was sent to any server.
Q : waiting in the QUEUE for a connection slot. This can only happen on
servers which have a 'maxconn' parameter set. No connection attempt
was made to any server.
C : waiting for CONNECTION to establish on the server. The server might
at most have noticed a connection attempt.
H : waiting for, receiving and processing server HEADERS (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.
T : the request was tarpitted. It has been held open on with the client
during the whole contimeout duration or untill the client closed.
- : 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 on new
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, or an attack.
D : the client provided a cookie designating a server which was DOWN,
so either the 'persist' option 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
- : 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.
P : a cookie was PROVIDED by the server and transmitted as-is.
R : the cookie provided by the server was REWRITTEN by the proxy.
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 give a lot of information about what was
happening when the session terminated. It can be helpful to detect server
saturation, network troubles, local system resource starvation, attacks, etc...
The most common termination flags combinations are indicated here.
Flags Reason
CR The client aborted before sending a full request. Most probably the
request was done by hand using a telnet client, and aborted early.
cR The client timed out before sending a full 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.
SC The server explicitly refused the connection (the proxy received a
TCP RST or an ICMP 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).
sC The connection to the server did not complete during contimeout.
PC The proxy refused to establish a connection to the server because the
maxconn limit has been reached. The listener's maxconn parameter may
be increased in the proxy configuration, as well as the global
maxconn parameter.
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. Anyway, this can only be
solved by system tuning.
cH The client timed out during a POST request. This is sometimes caused
by too large TCP MSS values for PPPoE networks which cannot transport
full-sized packets.
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.
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 the assigned server taking too long to
CT The client aborted while its session was tarpitted.
sQ The session spent too much time in queue and has been expired.
SH The server aborted before sending its full headers, or it crashed.
sH The server failed to reply during the srvtimeout delay, which
indicates too long transactions, probably caused by back-end
saturation. The only solutions are to fix the problem on the
application or to increase the 'srvtimeout' parameter to support
longer delays (at the risk of the client giving up anyway).
PR The proxy blocked the client's 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.
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.
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.
cD The client did not read any data for as long as the clitimeout delay.
This is often caused by network failures on the client side.
CD The client unexpectedly aborted during data transfer. This is either
caused by a browser crash, or by a keep-alive session between the
server and the client terminated first by the client.
sD The server did nothing during the srvtimeout delay. This is often
caused by too short timeouts on L4 equipements before the server
(firewalls, load-balancers, ...).
4.2.5) Non-printable characters
As of version 1.1.29, non-printable characters are not sent as-is into log
files, but are converted to their two-digits hexadecimal representation,
prefixed by the character '#'. The only characters that can now be logged
without being escaped are between 32 and 126 (inclusive). Obviously, the
escape character '#' is also encoded to avoid any ambiguity. It is the same for
the character '"', as well as '{', '|' and '}' when logging headers.
4.2.6) Capturing HTTP headers and cookies
Version 1.1.23 brought cookie capture, and 1.1.29 the header capture. All this
is performed using the 'capture' keyword.
Cookie capture makes it easy to track a complete user session. The syntax is :
capture cookie <cookie_prefix> len <capture_length>
This will enable cookie capture from both requests and responses. 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.
The FIRST cookie whose name starts with <cookie_prefix> will be captured, and
logged as 'NAME=value', without exceeding <capture_length> characters (64 max).
When the cookie name is fixed and known, it's preferable to suffix '=' to it to
ensure that no other cookie will be logged.
Examples :
# capture the first cookie whose name starts with "ASPSESSION"
capture cookie ASPSESSION len 32
# capture the first cookie whose name is exactly "vgnvisitor"
capture cookie vgnvisitor= len 32
In the logs, the field preceeding the completion indicator contains the cookie
value as sent by the server, preceeded by the cookie value as sent by the
client. Each of these field is replaced with '-' when no cookie was seen or
when the option is disabled.
Header captures have a different goal. They are useful to track unique request
identifiers set by a previous 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. As for cookie captures, it is both
possible to include request headers and response headers at the same time. The
syntax is :
capture request header <name> len <max length>
capture response header <name> len <max length>
Note: Header names are not case-sensitive.
# keep the name of the virtual server
capture request header Host len 20
# keep the amount of data uploaded during a POST
capture request header Content-Length len 10
# note the expected cache behaviour on the response
capture response header Cache-Control len 8
# note the URL location during a redirection
capture response header Location len 20
Non-existant headers are logged as empty strings, and if one header appears more
than once, only its last occurence will be kept. 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.
Example :
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
Log :
Aug 9 20:26:09 localhost haproxy[2022]: [09/Aug/2004:20:26:09] relais-http netcache 0/0/0/162/+162 200 +350 - - ---- 0/0/0 0/0 {||http://fr.f416.mail.} {|864|private||} "GET"
Aug 9 20:30:46 localhost haproxy[2022]: [09/Aug/2004:20:30:46] relais-http netcache 0/0/0/182/+182 200 +279 - - ---- 0/0/0 0/0 {||} {Formilux/0.1.8|3495|||} "GET HTTP/1.1"
Aug 9 20:30:46 localhost haproxy[2022]: [09/Aug/2004:20:30:46] relais-http netcache 0/0/2/126/+128 200 +223 - - ---- 0/0/0 0/0 {||} {Apache/2.0.40 (Red H|9068|||} "GET HTTP/1.1"
4.2.7) Examples of logs
- haproxy[674]: [15/Oct/2003:08:31:57] relais-http Srv1 6559/0/7/147/6723 200 243 - - ---- 1/3/5 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]: [15/Oct/2003:08:31:57] relais-http Srv1 6559/1230/7/147/6870 200 243 - - ---- 99/239/324 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]: [15/Oct/2003:08:32:17] relais-http Srv1 9/0/7/14/+30 200 +243 - - ---- 1/3/3 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 transfering 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]: [15/Oct/2003:08:32:17] relais-http Srv1 9/0/7/14/30 502 243 - - PH-- 0/2/3 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 it blocked sensible information which risked
being cached. In this case, the response is replaced with a '502 bad
- haproxy[18113]: [15/Oct/2003:15:18:55] relais-http <NOSRV> -1/-1/-1/-1/8490 -1 0 - - CR-- 0/2/2 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 the server.
- haproxy[18113]: [15/Oct/2003:15:19:06] relais-http <NOSRV> -1/-1/-1/-1/50001 408 0 - - cR-- 2/2 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 the server, but the proxy could send a 408 return code
to the client.
- haproxy[18989]: [15/Oct/2003:15:24:28] relais-tcp Srv1 0/0/5007 0 cD 0/0/0 0/0
=> This is a 'tcplog' entry. Client-side time-out ('c----') occured after 5s.
- haproxy[18989]: [15/Oct/2003:15:26:31] relais-http Srv1 3183/-1/-1/-1/11215 503 0 - - SC-- 115/202/205 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 attemps of 2 seconds
(config says 'retries 3'), then a 503 error code was sent 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.
4.3) HTTP header manipulation
In HTTP mode, it is possible to rewrite, add or delete some of the request and
response headers based on regular expressions. It is also possible to block a
request or a response if a particular header matches a regular expression,
which is enough to stops most elementary protocol attacks, and to protect
against information leak from the internal network. But there is a limitation
to this : since haproxy's HTTP engine knows nothing about keep-alive, only
headers passed during the first request of a TCP session will be seen. All
subsequent headers will be considered data only and not analyzed. Furthermore,
haproxy doesn't touch data contents, it stops at the end of headers.
The syntax is :
reqadd <string> to add a header to the request
reqrep <search> <replace> to modify the request
reqirep <search> <replace> same, but ignoring the case
reqdel <search> to delete a header in the request
reqidel <search> same, but ignoring the case
reqallow <search> definitely allow a request if a header matches <search>
reqiallow <search> same, but ignoring the case
reqdeny <search> denies a request if a header matches <search>
reqideny <search> same, but ignoring the case
reqpass <search> ignore a header matching <search>
reqipass <search> same, but ignoring the case
reqtarpit <search> tarpit a request matching <search>
reqitarpit <search> same, but ignoring the case
rspadd <string> to add a header to the response
rsprep <search> <replace> to modify the response
rspirep <search> <replace> same, but ignoring the case
rspdel <search> to delete the response
rspidel <search> same, but ignoring the case
rspdeny <search> replaces a response with a HTTP 502 if a header matches <search>
rspideny <search> same, but ignoring the case
<search> is a POSIX regular expression (regex) which supports grouping through
parenthesis (without the backslash). Spaces and other delimiters must be
prefixed with a backslash ('\') to avoid confusion with a field delimiter.
Other characters may be prefixed with a backslash to change their meaning :
\t for a tab
\r for a carriage return (CR)
\n for a new line (LF)
\ to mark a space and differentiate it from a delimiter
\# to mark a sharp and differentiate it from a comment
\\ to use a backslash in a regex
\\\\ to use a backslash in the text (*2 for regex, *2 for haproxy)
\xXX to write the ASCII hex code XX as in the C language
<replace> contains the string to be used to replace the largest portion of text
matching the regex. It can make use of the special characters above, and can
reference a substring delimited by parenthesis in the regex, by the group
numerical order from 0 to 9 (0 being the entire line). In this case, you would
write a backslash ('\') immediately followed by one digit indicating the group
<string> represents the string which will systematically be added after the last
header line. It can also use special characters above.
Notes :
- the first line is considered as a header, which makes it possible to rewrite
or filter HTTP requests URIs or response codes.
- 'reqrep' is the equivalent of 'cliexp' in version 1.0, and 'rsprep' is the
equivalent of 'srvexp' in 1.0. Those names are still supported but
- for performances reasons, the number of characters added to a request or to
a response is limited to 4096 since version 1.1.5 (it was 256 before). This
value is easy to modify in the code if needed (#define). If it is too short
on occasional uses, it is possible to gain some space by removing some
useless headers before adding new ones.
- a denied request will generate an "HTTP 403 forbidden" response, while a
denied response will generate an "HTTP 502 Bad gateway" response.
- a tarpitted request will be held open on the client side for a duration
defined in the contimeout parameter, or untill the client aborts. Nothing
will be sent to any server. When the timeout is reached, the proxy will
reply with a 500 server error response so that the attacker does not
suspect it has been tarpitted. The logs may report the 500, but the
termination flags will indicate 'PT' in this case.
Examples :
###### a few examples ######
# rewrite '' instead of '' for GET and POST requests
reqrep ^(GET\ .*)(*) \\3
reqrep ^(POST\ .*)(*) \\3
# force proxy connections to close
reqirep ^Proxy-Connection:.* Proxy-Connection:\ close
# rewrite locations
rspirep ^(Location:\ )([^:]*://[^/]*)(.*) \1\3
###### A full configuration being used on production ######
# Every header should end with a colon followed by one space.
reqideny ^[^:\ ]*[\ ]*$
# block Apache chunk exploit
reqideny ^Transfer-Encoding:[\ ]*chunked
reqideny ^Host:\ apache-
# block annoying worms that fill the logs...
reqideny ^[^:\ ]*\ .*(\.|%2e)(\.|%2e)(%2f|%5c|/|\\\\)
reqideny ^[^:\ ]*\ ([^\ ]*\ [^\ ]*\ |.*%00)
reqideny ^[^:\ ]*\ .*<script
reqideny ^[^:\ ]*\ .*/(root\.exe\?|cmd\.exe\?|default\.ida\?)
# tarpit attacks on the login page.
reqtarpit ^[^:\ ]*\ .*\.php?login=[^0-9]
# allow other syntactically valid requests, and block any other method
reqipass ^(GET|POST|HEAD|OPTIONS)\ /.*\ HTTP/1\.[01]$
reqipass ^OPTIONS\ \\*\ HTTP/1\.[01]$
reqideny ^[^:\ ]*\
# force connection:close, thus disabling HTTP keep-alive
option httpclose
# change the server name
rspidel ^Server:\
rspadd Server:\ Formilux/0.1.8
Also, the 'forwardfor' option creates an HTTP 'X-Forwarded-For' header which
contains the client's IP address. This is useful to let the final web server
know what the client address was (eg for statistics on domains). Starting with
version 1.3.8, it is possible to specify the "except" keyword followed by a
source IP address or network for which no header will be added. This is very
useful when another reverse-proxy which already adds the header runs on the
same machine or in a known DMZ, the most common case being the local use of
stunnel on the same system.
Last, the 'httpclose' option removes any 'Connection' header both ways, and
adds a 'Connection: close' header in each direction. This makes it easier to
disable HTTP keep-alive than the previous 4-rules block.
Example :
listen http_proxy
mode http
log global
option httplog
option dontlognull
option forwardfor except
option httpclose
Note that some HTTP servers do not necessarily close the connections when they
receive the 'Connection: close', and if the client does not close either, then
the connection will be maintained up to the time-out. This translates into high
number of simultaneous sessions and high global session times in the logs. To
workaround this, a new option 'forceclose' appeared in version 1.2.9 to enforce
the closing of the outgoing server channel as soon as the server begins to
reply and only if the request buffer is empty. Note that this should NOT be
used if CONNECT requests are expected between the client and the server. The
'forceclose' option implies the 'httpclose' option.
Example :
listen http_proxy
mode http
log global
option httplog
option dontlognull
option forwardfor
option forceclose
4.4) Load balancing with persistence
Combining cookie insertion with internal load balancing allows to transparently
bring persistence to applications. The principle is quite simple :
- assign a cookie value to each server
- enable the load balancing between servers
- insert a cookie into responses resulting from the balancing algorithm
(indirect accesses), end ensure that no upstream proxy will cache it.
- remove the cookie in the request headers so that the application never sees
Example :
listen application
mode http
cookie SERVERID insert nocache indirect
balance roundrobin
server srv1 cookie server01 check
server srv2 cookie server02 check
The other solution brought by versions 1.1.30 and 1.2.3 is to reuse a cookie
from the server, and prefix the server's name to it. In this case, don't forget
to force "httpclose" mode so that you can be assured that every subsequent
request will have its cookie fixed.
listen application
mode http
cookie JSESSIONID prefix
balance roundrobin
server srv1 cookie srv1 check
server srv2 cookie srv2 check
option httpclose
4.5) Protection against information leak from the servers
In versions 1.1.28/1.2.1, a new option 'checkcache' was created. It carefully
checks 'Cache-control', 'Pragma' and 'Set-cookie' headers in server response
to check if there's a risk of caching a cookie on a client-side proxy. When this
option is enabled, the only responses which can be delivered to the client are :
- all those without 'Set-Cookie' header ;
- all those with a return code other than 200, 203, 206, 300, 301, 410,
provided that the server has not set a 'Cache-control: public' header ;
- all those that come from a POST request, provided that the server has not
set a 'Cache-Control: public' header ;
- those with a 'Pragma: no-cache' header
- those with a 'Cache-control: private' header
- those with a 'Cache-control: no-store' header
- those with a 'Cache-control: max-age=0' header
- those with a 'Cache-control: s-maxage=0' header
- those with a 'Cache-control: no-cache' header
- those with a 'Cache-control: no-cache="set-cookie"' header
- those with a 'Cache-control: no-cache="set-cookie,' header
(allowing other fields after set-cookie)
If a response doesn't respect these requirements, then it will be blocked just
as if it was from an 'rspdeny' filter, with an "HTTP 502 bad gateway". The
session state shows "PH--" meaning that the proxy blocked the response during
headers processing. Additionnaly, an alert will be sent in the logs so that
admins are told that there's something to be done.
4.6) Customizing errors
Some situations can make haproxy return an HTTP error code to the client :
- invalid or too long request => HTTP 400
- request not completely sent in time => HTTP 408
- forbidden request (matches a deny filter) => HTTP 403
- internal error in haproxy => HTTP 500
- the server returned an invalid or incomplete response => HTTP 502
- no server was available to handle the request => HTTP 503
- the server failed to reply in time => HTTP 504
A succint error message taken from the RFC accompanies these return codes.
But depending on the clients knowledge, it may be better to return custom, user
friendly, error pages. This is made possible in two ways, one involving a
redirection to a known server, and another one consisting in returning a local
4.6.1) Relocation
An error relocation is achieved using the 'errorloc' command :
errorloc <HTTP_code> <location>
Instead of generating an HTTP error <HTTP_code> among those above, the proxy
will return a temporary redirection code (HTTP 302) towards the address
specified in <location>. This address may be either relative to the site or
absolute. Since this request will be handled by the client's browser, it's
mandatory that the returned address be reachable from the outside.
Example :
listen application
errorloc 400 /badrequest.html
errorloc 403 /forbidden.html
errorloc 408 /toolong.html
errorloc 500
errorloc 502
errorloc 503
errorloc 504
Note: RFC2616 says that a client must reuse the same method to fetch the
Location returned by a 302, which causes problems with the POST method.
The return code 303 was designed explicitly to force the client to fetch the
Location URL with the GET method, but there are some browsers pre-dating
HTTP/1.1 which don't support it. Anyway, most browsers still behave with 302 as
if it was a 303. In order to allow the user to chose, versions 1.1.31 and 1.2.5
bring two new keywords to replace 'errorloc' : 'errorloc302' and 'errorloc303'.
They are preffered over errorloc (which still does 302). Consider using
errorloc303 everytime you know that your clients support HTTP 303 responses..
4.6.2) Local files
Sometimes, it is desirable to change the returned error without resorting to
redirections. The second method consists in loading local files during startup
and send them as pure HTTP content upon error. This is what the 'errorfile'
keyword does.
Warning, there are traps to consider :
- The files are loaded while parsing configuration, before doing a chroot().
Thus, they are relative to the real filesystem. For this reason, it is
recommended to pass an absolute path to those files.
- The contents of those files is not HTML, but real HTTP protocol with
possible HTML body. So the first line and headers are mandatory. Ideally,
every line in the HTTP part should end with CR-LF for maximum compatibility.
- The response is limited to the buffer size (BUSIZE), generally 8 or 16 kB.
- The response should not include references to the local server, in order to
avoid infinite loops on the browser in case of local failure.
Example :
errorfile 400 /etc/haproxy/errorfiles/400badreq.http
errorfile 403 /etc/haproxy/errorfiles/403forbid.http
errorfile 503 /etc/haproxy/errorfiles/503sorry.http
4.7) Modifying default values
Version 1.1.22 introduced the notion of default values, which eliminates the
pain of often repeating common parameters between many instances, such as
logs, timeouts, modes, etc...
Default values are set in a 'defaults' section. Each of these section clears
all previously set default parameters, so there may be as many default
parameters as needed. Only the last one before a 'listen' section will be
used for this section. The 'defaults' section uses the same syntax as the
'listen' section, for the supported parameters. The 'defaults' keyword ignores
everything on its command line, so that fake instance names can be specified
there for better clarity.
In version 1.1.28/1.2.1, only those parameters can be preset in the 'default'
section :
- log (the first and second one)
- mode { tcp, http, health }
- balance { roundrobin }
- disabled (to disable every further instances)
- enabled (to enable every further instances, this is the default)
- contimeout, clitimeout, srvtimeout, grace, retries, maxconn
- option { redispatch, transparent, keepalive, forwardfor, logasap, httpclose,
checkcache, httplog, tcplog, dontlognull, persist, httpchk }
- redispatch, redisp, transparent, source { addr:port }
- cookie, capture
- errorloc
As of 1.1.24, it is not possible to put certain parameters in a 'defaults'
section, mainly regular expressions and server configurations :
- dispatch, server,
- req*, rsp*
Last, there's no way yet to change a boolean option from its assigned default
value. So if an 'option' statement is set in a 'defaults' section, the only
way to flush it is to redefine a new 'defaults' section without this 'option'.
Examples :
defaults applications TCP
log global
mode tcp
balance roundrobin
clitimeout 180000
srvtimeout 180000
contimeout 4000
retries 3
listen app_tcp1
server srv1 check port 6000 inter 10000
server srv2 backup
listen app_tcp2
server srv1 check port 6000 inter 10000
server srv2 backup
defaults applications HTTP
log global
mode http
option httplog
option forwardfor
option dontlognull
balance roundrobin
clitimeout 20000
srvtimeout 20000
contimeout 4000
retries 3
listen app_http1
cookie SERVERID postonly insert indirect
capture cookie userid= len 10
server srv1 cookie srv1 check port 8080 inter 1000
server srv1 cookie srv2 check port 8080 inter 1000
# this empty section voids all default parameters
4.8) Status report in HTML page
Starting with 1.2.14, it is possible for HAProxy to intercept requests for a
particular URI and return a full report of the proxy's activity and servers
statistics. This is available through the 'stats' keyword, associated to any
such options :
- stats enable
- stats uri <uri prefix>
- stats realm <authentication realm>
- stats auth <user:password>
- stats scope <proxy_id> | '.'
By default, the status report is disabled. Specifying any combination above
enables it for the proxy instance referencing it. The easiest solution is to
use "stats enable" which will enable the report with default parameters :
- default URI : "/haproxy?stats" (CONFIG_STATS_DEFAULT_URI)
- default auth : unspecified (no authentication)
- default realm : "HAProxy Statistics" (CONFIG_STATS_DEFAULT_REALM)
- default scope : unspecified (access to all instances)
The "stats uri <uri_prefix>" option allows one to intercept another URI prefix.
Note that any URI that BEGINS with this string will match. For instance, one
proxy instance might be dedicated to status page only and would reply to any
Example :
# catches any URI and returns the status page.
listen stats :8080
mode http
stats uri /
The "stats auth <user:password>" option enables Basic authentication and adds a
valid user:password combination to the list of authorized accounts. The user
and password are passed in the configuration file as clear text, and since this
is HTTP Basic authentication, you should be aware that it transits as clear
text on the network, so you must not use any sensible account. The list is
unlimited in order to provide easy accesses to developpers or customers.
The "stats realm <realm>" option defines the "realm" name which is displayed
in the popup box when the browser asks for a password. It's important to ensure
that this one is not used by the application, otherwise the browser will try to
use a cached one from the application. Note that any space in the realm name
should be escaped with a backslash ('\').
The "stats scope <proxy_id>" option limits the scope of the status report. By
default, all proxy instances are listed. But under some circumstances, it would
be better to limit the listing to some proxies or only to the current one. This
is what this option does. The special proxy name "." (a single dot) references
the current proxy. The proxy name can be repeated multiple times, even for
proxies defined later in the configuration or some which do not exist. The name
is the one which appears after the 'listen' keyword.
Example :
# simple application with authenticated embedded status report
listen app1
mode http
option httpclose
balance roundrobin
cookie SERVERID postonly insert indirect
server srv1 cookie srv1 check inter 1000
server srv1 cookie srv2 check inter 1000
stats uri /my_stats
stats realm Statistics\ for\ MyApp1-2
stats auth guest:guest
stats auth admin:AdMiN123
stats scope .
stats scope app2
# simple application with anonymous embedded status report
listen app2
mode http
option httpclose
balance roundrobin
cookie SERVERID postonly insert indirect
server srv1 cookie srv1 check inter 1000
server srv1 cookie srv2 check inter 1000
stats uri /my_stats
stats realm Statistics\ for\ MyApp2
stats scope .
listen admin_page :8080
mode http
stats uri /my_stats
stats realm Global\ statistics
stats auth admin:AdMiN123
Notes :
- The 'stats' options can also be specified in the 'defaults' section, in
which case it will provide the exact same configuration to all further
instances (hence the usefulness of the scope "."). However, if an instance
redefines any 'stats' parameter, defaults will not be used for this
- HTTP Basic authentication is very basic and unsecure from snooping. No
sensible password should be used, and be aware that there is no way to
remove it from the browser so it will be sent to the whole application
upon further accesses.
- It is very important that the 'option httpclose' is specified, otherwise
the proxy will not be able to detect the URI within keep-alive sessions
maintained between the browser and the servers, so the stats URI will be
forwarded unmodified to the server as if the option was not set.
5) Access lists
With version 1.3.10, a new concept of access lists (acl) was born. As it was
not necesary to reinvent the wheel, and because even long thoughts lead to
unsatisfying proposals, it was finally decided that something close to what
Squid provides would be a good compromise between features and ease of use.
The principle is very simple : acls are declared with a name, a test and a list
of valid values to check against during the test. Conditions are applied on
various actions, and those conditions apply a logical AND between acls. The
condition is then only met if all acls are true.
It is possible to use the reserved keyword "OR" in conditions, and it is
possible for an acl to be specified multiple times, even with various tests, in
which case the first one which returns true validates the ACL.
As of 1.3.12, only the following tests have been implemented :
Layer 3/4 :
src <ipv4_address>[/mask] ... : match IPv4 source address
dst <ipv4_address>[/mask] ... : match IPv4 destination address
src_port <range> ... : match source port range
dst_port <range> ... : match destination port range
dst_conn <range> ... : match #connections on frontend
Layer 7 :
method <HTTP method> ... : match HTTP method
req_ver <1.0|1.1> ... : match HTTP request version
resp_ver <1.0|1.1> ... : match HTTP response version
status <range> ... : match HTTP response status code in range
url <string> ... : exact string match on URI
url_reg <regex> ... : regex string match on URI
url_beg <string> ... : true if URI begins with <string>
url_end <string> ... : true if URI ends with <string>
url_sub <string> ... : true if URI contains <string>
url_dir <string> ... : true if URI contains <string> between slashes
url_dom <string> ... : true if URI contains <string> between slashes or dots
A 'range' is one or two integers which may be prefixed by an operator.
The syntax is :
[<op>] <low>[:<high>]
Where <op> can be :
'eq' : the tested value must be equal to <low> or within <low>..<high>
'le' : the tested value must be lower than or equal to <low>
'lt' : the tested value must be lower than <low>
'ge' : the tested value must be greater than or equal to <low>
'gt' : the tested value must be greater than <low>
When no operator is defined, 'eq' is assumed. Note that when the operator is
specified, it applies to all subsequent ranges of values until the end of the
line is reached or another operator is specified. Example :
acl status_error status 400:599
acl saturated_frt dst_conn ge 1000
acl invalid_ports src_port lt 512 ge 65535
Other ones are coming (headers, cookies, time, auth), it's just a matter of
time. It is also planned to be able to read the patterns from a file, as well
as to ignore the case for some of them.
The only command supporting a condition right now is the "block" command, which
blocks a request and returns a 403 if its condition is true (with the "if"
keyword), or if it is false (with the "unless" keyword).
Example :
acl options_uris url *
acl meth_option method OPTIONS
acl http_1.1 req_ver 1.1
acl allowed_meth method GET HEAD POST OPTIONS CONNECT
acl connect_meth method CONNECT
acl proxy_url url_beg http://
# block if reserved URI "*" used with a method other than "OPTIONS"
block if options_uris !meth_option
# block if the OPTIONS method is used with HTTP 1.0
block if meth_option !http_1.1
# allow non-proxy url with anything but the CONNECT method
block if !connect_meth !proxy_url
# block all unknown methods
block unless allowed_meth
Note: this documentation is very light but should permit one to start and above
all it should permit to work on the project without being slowed down too much
with the doc.
| System-specific setup |
Linux 2.4
-- cut here --
# set this to about 256/4M (16384 for 256M machine)
echo $MAXFILES > /proc/sys/fs/file-max
ulimit -n $MAXFILES
if [ -e /proc/sys/net/ipv4/ip_conntrack_max ]; then
echo 65536 > /proc/sys/net/ipv4/ip_conntrack_max
if [ -e /proc/sys/net/ipv4/netfilter/ip_ct_tcp_timeout_fin_wait ]; then
# 30 seconds for fin, 15 for time wait
echo 3000 > /proc/sys/net/ipv4/netfilter/ip_ct_tcp_timeout_fin_wait
echo 1500 > /proc/sys/net/ipv4/netfilter/ip_ct_tcp_timeout_time_wait
echo 0 > /proc/sys/net/ipv4/netfilter/ip_ct_tcp_log_invalid_scale
echo 0 > /proc/sys/net/ipv4/netfilter/ip_ct_tcp_log_out_of_window
echo 1024 60999 > /proc/sys/net/ipv4/ip_local_port_range
echo 30 > /proc/sys/net/ipv4/tcp_fin_timeout
echo 4096 > /proc/sys/net/ipv4/tcp_max_syn_backlog
echo 262144 > /proc/sys/net/ipv4/tcp_max_tw_buckets
echo 262144 > /proc/sys/net/ipv4/tcp_max_orphans
echo 300 > /proc/sys/net/ipv4/tcp_keepalive_time
echo 1 > /proc/sys/net/ipv4/tcp_tw_recycle
echo 0 > /proc/sys/net/ipv4/tcp_timestamps
echo 0 > /proc/sys/net/ipv4/tcp_ecn
echo 1 > /proc/sys/net/ipv4/tcp_sack
echo 0 > /proc/sys/net/ipv4/tcp_dsack
# auto-tuned on 2.4
#echo 262143 > /proc/sys/net/core/rmem_max
#echo 262143 > /proc/sys/net/core/rmem_default
echo 16384 65536 524288 > /proc/sys/net/ipv4/tcp_rmem
echo 16384 349520 699040 > /proc/sys/net/ipv4/tcp_wmem
-- cut here --
A FreeBSD port of HA-Proxy is now available and maintained, thanks to
Clement Laforet <>.
For more information :
-- end --
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