Apache HTTP Server Version 2.3
Apache HTTP Server Version 2.3
| Description: | Multi-protocol proxy/gateway server |
|---|---|
| Status: | Extension |
| Module Identifier: | proxy_module |
| Source File: | mod_proxy.c |
Do not enable proxying with ProxyRequests until you have secured your server. Open proxy servers are dangerous both to your
network and to the Internet at large.
mod_proxy and related modules implement a
proxy/gateway for Apache HTTP Server, supporting a number of popular
protocols as well as several different load balancing algorithms.
Third-party modules can add support for additional protocols and
load balancing algorithms.
A set of modules must be loaded into the server to provide the
necessary features. These modules can be included statically at
build time or dynamically via the
LoadModule directive).
The set must include:
mod_proxy, which provides basic proxy
capabilitiesmod_proxy_balancer and one or more
balancer modules, if load balancing is required. (See
mod_proxy_balancer for more information.)| Protocol | Module |
|---|---|
| AJP13 (Apache JServe Protocol version 1.3) | mod_proxy_ajp |
| CONNECT (for SSL) | mod_proxy_connect |
| FastCGI | mod_proxy_fcgi |
| ftp | mod_proxy_ftp |
| HTTP/0.9, HTTP/1.0, and HTTP/1.1 | mod_proxy_http |
| SCGI | mod_proxy_scgi |
In addition, extended features are provided by other modules.
Caching is provided by mod_cache and related
modules. The ability to contact remote servers using the SSL/TLS
protocol is provided by the SSLProxy* directives of
mod_ssl. These additional modules will need
to be loaded and configured to take advantage of these features.
BalancerMember NoProxy <Proxy> ProxyBadHeader ProxyBlock ProxyDomain ProxyErrorOverride ProxyIOBufferSize <ProxyMatch> ProxyMaxForwards ProxyPass ProxyPassInterpolateEnv ProxyPassMatch ProxyPassReverse ProxyPassReverseCookieDomain ProxyPassReverseCookiePath ProxyPreserveHost ProxyReceiveBufferSize ProxyRemote ProxyRemoteMatch ProxyRequests ProxySet ProxyStatus ProxyTimeout ProxyVia Forward Proxies and Reverse
Proxies/Gateways Basic Examples Workers Controlling access to your proxy Slow Startup Intranet Proxy Protocol Adjustments Request Bodies Reverse Proxy Request Headers
Apache HTTP Server can be configured in both a forward and reverse proxy (also known as gateway) mode.
An ordinary forward proxy is an intermediate server that sits between the client and the origin server. In order to get content from the origin server, the client sends a request to the proxy naming the origin server as the target and the proxy then requests the content from the origin server and returns it to the client. The client must be specially configured to use the forward proxy to access other sites.
A typical usage of a forward proxy is to provide Internet
access to internal clients that are otherwise restricted by a
firewall. The forward proxy can also use caching (as provided
by mod_cache) to reduce network usage.
The forward proxy is activated using the ProxyRequests directive. Because
forward proxies allow clients to access arbitrary sites through
your server and to hide their true origin, it is essential that
you secure your server so that only
authorized clients can access the proxy before activating a
forward proxy.
A reverse proxy (or gateway), by contrast, appears to the client just like an ordinary web server. No special configuration on the client is necessary. The client makes ordinary requests for content in the name-space of the reverse proxy. The reverse proxy then decides where to send those requests, and returns the content as if it was itself the origin.
A typical usage of a reverse proxy is to provide Internet users access to a server that is behind a firewall. Reverse proxies can also be used to balance load among several back-end servers, or to provide caching for a slower back-end server. In addition, reverse proxies can be used simply to bring several servers into the same URL space.
A reverse proxy is activated using the ProxyPass directive or the
[P] flag to the RewriteRule directive. It is
not necessary to turn ProxyRequests on in order to
configure a reverse proxy.
The examples below are only a very basic idea to help you get started. Please read the documentation on the individual directives.
In addition, if you wish to have caching enabled, consult
the documentation from mod_cache.
ProxyPass /foo http://foo.example.com/bar
ProxyPassReverse /foo http://foo.example.com/bar
ProxyRequests On
ProxyVia On
<Proxy *>
Require host internal.example.com
</Proxy>
The proxy manages the configuration of origin servers and their communication parameters in objects called workers. There are two built-in workers, the default forward proxy worker and the default reverse proxy worker. Additional workers can be configured explicitly.
The two default workers have a fixed configuration and will be used if no other worker matches the request. They do not use HTTP Keep-Alive or connection pooling. The TCP connections to the origin server will instead be opened and closed for each request.
Explicitly configured workers are identified by their URL.
They are usually created and configured using
ProxyPass or
ProxyPassMatch when used
for a reverse proxy:
ProxyPass /example http://backend.example.com connectiontimeout=5 timeout=30
This will create a worker associated with the origin server URL
http://backend.example.com and using the given timeout
values. When used in a forward proxy, workers are usually defined
via the ProxySet directive:
ProxySet http://backend.example.com connectiontimeout=5 timeout=30
or alternatively using Proxy
and ProxySet:
<Proxy http://backend.example.com>
ProxySet connectiontimeout=5 timeout=30
</Proxy>
Using explicitly configured workers in the forward mode is
not very common, because forward proxies usually communicate with many
different origin servers. Creating explicit workers for some of the
origin servers can still be useful, if they are used very often.
Explicitly configured workers have no concept of forward or reverse
proxying by themselves. They encapsulate a common concept of
communication with origin servers. A worker created by
ProxyPass for use in a
reverse proxy will be also used for forward proxy requests whenever
the URL to the origin server matches the worker URL and vice versa.
The URL identifying a direct worker is the URL of its origin server including any path components given:
ProxyPass /examples http://backend.example.com/examples
ProxyPass /docs http://backend.example.com/docs
This example defines two different workers, each using a separate connection pool and configuration.
Worker sharing happens if the worker URLs overlap, which occurs when the URL of some worker is a leading substring of the URL of another worker defined later in the configuration file. In the following example
ProxyPass /apps http://backend.example.com/ timeout=60
ProxyPass /examples http://backend.example.com/examples timeout=10
the second worker isn't actually created. Instead the first
worker is used. The benefit is, that there is only one connection pool,
so connections are more often reused. Note that all configuration attributes
given explicitly for the later worker will be ignored. This will be logged
as a warning. In the above example the resulting timeout value
for the URL /examples will be 60 instead
of 10!
If you want to avoid worker sharing, sort your worker definitions
by URL length, starting with the longest worker URLs. If you want to maximize
worker sharing use the reverse sort order. See also the related warning about
ordering ProxyPass directives.
Explicitly configured workers come in two flavors:
direct workers and (load) balancer workers.
They support many important configuration attributes which are
described below in the ProxyPass
directive. The same attributes can also be set using
ProxySet.
The set of options available for a direct worker
depends on the protocol, which is specified in the origin server URL.
Available protocols include ajp, fcgi,
ftp, http and scgi.
Balancer workers are virtual workers that use direct workers known as their members to actually handle the requests. Each balancer can have multiple members. When it handles a request, it chooses a member based on the configured load balancing algorithm.
A balancer worker is created if its worker URL uses
balancer as the protocol scheme.
The balancer URL uniquely identifies the balancer worker.
Members are added to a balancer using
BalancerMember.
You can control who can access your proxy via the <Proxy> control block as in
the following example:
<Proxy *>
Require ip 192.168.0
</Proxy>
For more information on access control directives, see
mod_authz_host.
Strictly limiting access is essential if you are using a
forward proxy (using the ProxyRequests directive).
Otherwise, your server can be used by any client to access
arbitrary hosts while hiding his or her true identity. This is
dangerous both for your network and for the Internet at large.
When using a reverse proxy (using the ProxyPass directive with
ProxyRequests Off), access control is less
critical because clients can only contact the hosts that you
have specifically configured.
See Also the Proxy-Chain-Auth environment variable.
If you're using the ProxyBlock directive, hostnames' IP addresses are looked up
and cached during startup for later match test. This may take a few
seconds (or more) depending on the speed with which the hostname lookups
occur.
An Apache httpd proxy server situated in an intranet needs to forward
external requests through the company's firewall (for this, configure
the ProxyRemote directive
to forward the respective scheme to the firewall proxy).
However, when it has to
access resources within the intranet, it can bypass the firewall when
accessing hosts. The NoProxy
directive is useful for specifying which hosts belong to the intranet and
should be accessed directly.
Users within an intranet tend to omit the local domain name from their
WWW requests, thus requesting "http://somehost/" instead of
http://somehost.example.com/. Some commercial proxy servers
let them get away with this and simply serve the request, implying a
configured local domain. When the ProxyDomain directive is used and the server is configured for proxy service, Apache httpd can return
a redirect response and send the client to the correct, fully qualified,
server address. This is the preferred method since the user's bookmark
files will then contain fully qualified hosts.
For circumstances where mod_proxy is sending
requests to an origin server that doesn't properly implement
keepalives or HTTP/1.1, there are two environment variables that can force the
request to use HTTP/1.0 with no keepalive. These are set via the
SetEnv directive.
These are the force-proxy-request-1.0 and
proxy-nokeepalive notes.
<Location /buggyappserver/>
ProxyPass http://buggyappserver:7001/foo/
SetEnv force-proxy-request-1.0 1
SetEnv proxy-nokeepalive 1
</Location>
Some request methods such as POST include a request body.
The HTTP protocol requires that requests which include a body
either use chunked transfer encoding or send a
Content-Length request header. When passing these
requests on to the origin server, mod_proxy_http
will always attempt to send the Content-Length. But
if the body is large and the original request used chunked
encoding, then chunked encoding may also be used in the upstream
request. You can control this selection using environment variables. Setting
proxy-sendcl ensures maximum compatibility with
upstream servers by always sending the
Content-Length, while setting
proxy-sendchunked minimizes resource usage by using
chunked encoding.
Under some circumstances, the server must spool request bodies to disk to satisfy the requested handling of request bodies. For example, this spooling will occur if the original body was sent with chunked encoding (and is large), but the administrator has asked for backend requests to be sent with Content-Length or as HTTP/1.0. This spooling can also occur if the request body already has a Content-Length header, but the server is configured to filter incoming request bodies.
LimitRequestBody only applies to
request bodies that the server will spool to disk
When acting in a reverse-proxy mode (using the ProxyPass directive, for example),
mod_proxy_http adds several request headers in
order to pass information to the origin server. These headers
are:
X-Forwarded-ForX-Forwarded-HostHost
HTTP request header.X-Forwarded-ServerBe careful when using these headers on the origin server, since
they will contain more than one (comma-separated) value if the
original request already contained one of these headers. For
example, you can use %{X-Forwarded-For}i in the log
format string of the origin server to log the original clients IP
address, but you may get more than one address if the request
passes through several proxies.
See also the ProxyPreserveHost and ProxyVia directives, which control
other request headers.
| Description: | Add a member to a load balancing group |
|---|---|
| Syntax: | BalancerMember [balancerurl] url [key=value [key=value ...]] |
| Context: | directory |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | BalancerMember is only available in Apache HTTP Server 2.2 and later. |
This directive adds a member to a load balancing group. It could be used
within a <Proxy balancer://...> container
directive, and can take any of the key value pair parameters available to
ProxyPass directives.
One additional parameter is available only to BalancerMember directives:
loadfactor. This is the member load factor - a number between 1
(default) and 100, which defines the weighted load to be applied to the
member in question.
The balancerurl is only needed when not in <Proxy balancer://...>
container directive. It corresponds to the url of a balancer defined in
ProxyPass directive.
| Description: | Hosts, domains, or networks that will be connected to directly |
|---|---|
| Syntax: | NoProxy host [host] ... |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
This directive is only useful for Apache httpd proxy servers within
intranets. The NoProxy directive specifies a
list of subnets, IP addresses, hosts and/or domains, separated by
spaces. A request to a host which matches one or more of these is
always served directly, without forwarding to the configured
ProxyRemote proxy server(s).
ProxyRemote * http://firewall.example.com:81
NoProxy .example.com 192.168.112.0/21
The host arguments to the NoProxy
directive are one of the following type list:
A Domain is a partially qualified DNS domain name, preceded by a period. It represents a list of hosts which logically belong to the same DNS domain or zone (i.e., the suffixes of the hostnames are all ending in Domain).
.com .example.org.
To distinguish Domains from Hostnames (both syntactically and semantically; a DNS domain can have a DNS A record, too!), Domains are always written with a leading period.
Domain name comparisons are done without regard to the case, and
Domains are always assumed to be anchored in the root of the
DNS tree, therefore two domains .ExAmple.com and
.example.com. (note the trailing period) are considered
equal. Since a domain comparison does not involve a DNS lookup, it is much
more efficient than subnet comparison.
A SubNet is a partially qualified internet address in numeric (dotted quad) form, optionally followed by a slash and the netmask, specified as the number of significant bits in the SubNet. It is used to represent a subnet of hosts which can be reached over a common network interface. In the absence of the explicit net mask it is assumed that omitted (or zero valued) trailing digits specify the mask. (In this case, the netmask can only be multiples of 8 bits wide.) Examples:
192.168 or 192.168.0.0255.255.0.0)192.168.112.0/21192.168.112.0/21 with a netmask of 21
valid bits (also used in the form 255.255.248.0)As a degenerate case, a SubNet with 32 valid bits is the equivalent to an IPAddr, while a SubNet with zero valid bits (e.g., 0.0.0.0/0) is the same as the constant _Default_, matching any IP address.
A IPAddr represents a fully qualified internet address in numeric (dotted quad) form. Usually, this address represents a host, but there need not necessarily be a DNS domain name connected with the address.
192.168.123.7
An IPAddr does not need to be resolved by the DNS system, so it can result in more effective apache performance.
A Hostname is a fully qualified DNS domain name which can be resolved to one or more IPAddrs via the DNS domain name service. It represents a logical host (in contrast to Domains, see above) and must be resolvable to at least one IPAddr (or often to a list of hosts with different IPAddrs).
prep.ai.example.edu
www.example.org
In many situations, it is more effective to specify an IPAddr in place of a Hostname since a DNS lookup can be avoided. Name resolution in Apache httpd can take a remarkable deal of time when the connection to the name server uses a slow PPP link.
Hostname comparisons are done without regard to the case,
and Hostnames are always assumed to be anchored in the root
of the DNS tree, therefore two hosts WWW.ExAmple.com
and www.example.com. (note the trailing period) are
considered equal.
| Description: | Container for directives applied to proxied resources |
|---|---|
| Syntax: | <Proxy wildcard-url> ...</Proxy> |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
Directives placed in <Proxy>
sections apply only to matching proxied content. Shell-style wildcards are
allowed.
For example, the following will allow only hosts in
yournetwork.example.com to access content via your proxy
server:
<Proxy *>
Require host yournetwork.example.com
</Proxy>
The following example will process all files in the foo
directory of example.com through the INCLUDES
filter when they are sent through the proxy server:
<Proxy http://example.com/foo/*>
SetOutputFilter INCLUDES
</Proxy>
| Description: | Determines how to handle bad header lines in a response |
|---|---|
| Syntax: | ProxyBadHeader IsError|Ignore|StartBody |
| Default: | ProxyBadHeader IsError |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | Available in Apache HTTP Server 2.0.44 and later |
The ProxyBadHeader directive determines the
behaviour of mod_proxy if it receives syntactically invalid
response header lines (i.e. containing no colon) from the origin
server. The following arguments are possible:
IsErrorIgnoreStartBody| Description: | Words, hosts, or domains that are banned from being proxied |
|---|---|
| Syntax: | ProxyBlock *|word|host|domain
[word|host|domain] ... |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
The ProxyBlock directive specifies a list of
words, hosts and/or domains, separated by spaces. HTTP, HTTPS, and
FTP document requests to sites whose names contain matched words,
hosts or domains are blocked by the proxy server. The proxy
module will also attempt to determine IP addresses of list items which
may be hostnames during startup, and cache them for match test as
well. That may slow down the startup time of the server.
ProxyBlock news.example.com auctions.example.com friends.example.com
Note that example would also be sufficient to match any
of these sites.
Hosts would also be matched if referenced by IP address.
Note also that
ProxyBlock *
blocks connections to all sites.
| Description: | Default domain name for proxied requests |
|---|---|
| Syntax: | ProxyDomain Domain |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
This directive is only useful for Apache httpd proxy servers within
intranets. The ProxyDomain directive specifies
the default domain which the apache proxy server will belong to. If a
request to a host without a domain name is encountered, a redirection
response to the same host with the configured Domain appended
will be generated.
ProxyRemote * http://firewall.example.com:81
NoProxy .example.com 192.168.112.0/21
ProxyDomain .example.com
| Description: | Override error pages for proxied content |
|---|---|
| Syntax: | ProxyErrorOverride On|Off |
| Default: | ProxyErrorOverride Off |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | Available in version 2.0 and later |
This directive is useful for reverse-proxy setups, where you want to
have a common look and feel on the error pages seen by the end user.
This also allows for included files (via
mod_include's SSI) to get
the error code and act accordingly (default behavior would display
the error page of the proxied server, turning this on shows the SSI
Error message).
This directive does not affect the processing of informational (1xx), normal success (2xx), or redirect (3xx) responses.
| Description: | Determine size of internal data throughput buffer |
|---|---|
| Syntax: | ProxyIOBufferSize bytes |
| Default: | ProxyIOBufferSize 8192 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
The ProxyIOBufferSize directive adjusts the size
of the internal buffer, which is used as a scratchpad for the data between
input and output. The size must be at least 512.
In almost every case there's no reason to change that value.
If used with AJP this directive sets the maximum AJP packet size in
bytes. If you change it from the default, you must also change the
packetSize attribute of your AJP connector on the
Tomcat side! The attribute packetSize is only available
in Tomcat 5.5.20+ and 6.0.2+
Normally it is not necessary to change the maximum packet size. Problems with the default value have been reported when sending certificates or certificate chains.
| Description: | Container for directives applied to regular-expression-matched proxied resources |
|---|---|
| Syntax: | <ProxyMatch regex> ...</ProxyMatch> |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
The <ProxyMatch> directive is
identical to the <Proxy> directive, except it matches URLs
using regular expressions.
| Description: | Maximium number of proxies that a request can be forwarded through |
|---|---|
| Syntax: | ProxyMaxForwards number |
| Default: | ProxyMaxForwards -1 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | Available in Apache HTTP Server 2.0 and later; default behaviour changed in 2.2.7/2.3 |
The ProxyMaxForwards directive specifies the
maximum number of proxies through which a request may pass, if there's no
Max-Forwards header supplied with the request. This may
be set to prevent infinite proxy loops, or a DoS attack.
ProxyMaxForwards 15
Note that setting ProxyMaxForwards is a
violation of the HTTP/1.1 protocol (RFC2616), which forbids a Proxy
setting Max-Forwards if the Client didn't set it.
Earlier Apache httpd versions would always set it. A negative
ProxyMaxForwards value, including the
default -1, gives you protocol-compliant behaviour, but may
leave you open to loops.
| Description: | Maps remote servers into the local server URL-space |
|---|---|
| Syntax: | ProxyPass [path] !|url [key=value
[key=value ...]] [nocanon] [interpolate] |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
This directive allows remote servers to be mapped into the space of the local server; the local server does not act as a proxy in the conventional sense, but appears to be a mirror of the remote server. The local server is often called a reverse proxy or gateway. The path is the name of a local virtual path; url is a partial URL for the remote server and cannot include a query string.
ProxyRequests directive should
usually be set off when using
ProxyPass.Suppose the local server has address http://example.com/;
then
<Location /mirror/foo/>
ProxyPass http://backend.example.com/
</Location>
will cause a local request for
http://example.com/mirror/foo/bar to be internally converted
into a proxy request to http://backend.example.com/bar.
The following alternative syntax is possible, however carries a performance penalty when present in large numbers:
ProxyPass /mirror/foo/ http://backend.example.com/
If the first argument ends with a trailing /, the second argument should also end with a trailing / and vice versa. Otherwise the resulting requests to the backend may miss some needed slashes and do not deliver the expected results.
The ! directive is useful in situations where you don't want
to reverse-proxy a subdirectory, e.g.
<Location /mirror/foo/>
ProxyPass http://backend.example.com/
</Location>
<Location /mirror/foo/i>
ProxyPass !
</Location>
ProxyPass /mirror/foo/i !
ProxyPass /mirror/foo http://backend.example.com
will proxy all requests to /mirror/foo to
backend.example.com except requests made to
/mirror/foo/i.
The configured ProxyPass
and ProxyPassMatch
rules are checked in the order of configuration. The first rule that
matches wins. So usually you should sort conflicting
ProxyPass rules starting with the
longest URLs first. Otherwise later rules for longer URLS will be hidden
by any earlier rule which uses a leading substring of the URL. Note that
there is some relation with worker sharing. In contrast, only one
ProxyPass directive can be placed
in a Location block, and the most
specific location will take precedence.
For the same reasons exclusions must come before the
general ProxyPass directives.
In Apache HTTP Server 2.1 and later, mod_proxy supports pooled
connections to a backend server. Connections created on demand
can be retained in a pool for future use. Limits on the pool size
and other settings can be coded on
the ProxyPass directive
using key=value parameters, described in the table
below.
By default, mod_proxy will allow and retain the maximum number of
connections that could be used simultaneously by that web server child
process. Use the max parameter to reduce the number from
the default. Use the ttl parameter to set an optional
time to live; connections which have been unused for at least
ttl seconds will be closed. ttl can be used
to avoid using a connection which is subject to closing because of the
backend server's keep-alive timeout.
The pool of connections is maintained per web server child
process, and max and other settings are not coordinated
among all child processes, except when only one child process is allowed
by configuration or MPM design.
ProxyPass /example http://backend.example.com max=20 ttl=120 retry=300
| Parameter | Default | Description |
|---|---|---|
| min | 0 | Minimum number of connection pool entries, unrelated to the actual number of connections. This only needs to be modified from the default for special circumstances where heap memory associated with the backend connections should be preallocated or retained. |
| max | 1...n | Maximum number of connections that will be allowed to the
backend server. The default for this limit is the number of threads
per process in the active MPM. In the Prefork MPM, this is always 1,
while with other MPMs it is controlled by the
ThreadsPerChild directive. |
| smax | max | Retained connection pool entries above this limit are freed
during certain operations if they have been unused for longer than
the time to live, controlled by the ttl parameter. If
the connection pool entry has an associated connection, it will be
closed. This only needs to be modified from the default for special
circumstances where connection pool entries and any associated
connections which have exceeded the time to live need to be freed or
closed more aggressively. |
| acquire | - | If set this will be the maximum time to wait for a free
connection in the connection pool, in milliseconds. If there are no free
connections in the pool the Apache httpd will return SERVER_BUSY
status to the client.
|
| connectiontimeout | timeout | Connect timeout in seconds. The number of seconds Apache httpd waits for the creation of a connection to the backend to complete. By adding a postfix of ms the timeout can be also set in milliseconds. |
| disablereuse | Off | This parameter should be used when you want to force mod_proxy
to immediately close a connection to the backend after being used, and
thus, disable its persistent connection and pool for that backend.
This helps in various situations where a firewall between Apache
httpd and
the backend server (regardless of protocol) tends to silently
drop connections or when backends themselves may be under round-
robin DNS. To disable connection pooling reuse,
set this property value to On.
|
| flushpackets | off | Determines whether the proxy module will auto-flush the output brigade after each "chunk" of data. 'off' means that it will flush only when needed, 'on' means after each chunk is sent and 'auto' means poll/wait for a period of time and flush if no input has been received for 'flushwait' milliseconds. Currently this is in effect only for AJP. |
| flushwait | 10 | The time to wait for additional input, in milliseconds, before flushing the output brigade if 'flushpackets' is 'auto'. |
| iobuffersize | 8192 | Adjusts the size of the internal scratchpad IO buffer. This allows you
to override the ProxyIOBufferSize for a specific worker.
This must be at least 512 or set to 0 for the system default of 8192.
|
| keepalive | Off | This parameter should be used when you have a firewall between your
Apache httpd and the backend server, who tend to drop inactive connections.
This flag will tell the Operating System to send The frequency of initial and subsequent TCP keepalive probes depends on global OS settings, and may be as high as 2 hours. To be useful, the frequency configured in the OS must be smaller than the threshold used by the firewall. |
| lbset | 0 | Sets the load balancer cluster set that the worker is a member of. The load balancer will try all members of a lower numbered lbset before trying higher numbered ones. |
| ping | 0 | Ping property tells the webserver to "test" the connection to
the backend before forwarding the request. For AJP, it causes
mod_proxy_ajpto send a CPING
request on the ajp13 connection (implemented on Tomcat 3.3.2+, 4.1.28+
and 5.0.13+). For HTTP, it causes mod_proxy_http
to send a 100-Continue to the backend (only valid for
HTTP/1.1 - for non HTTP/1.1 backends, this property has no
effect). In both cases the parameter is the delay in seconds to wait
for the reply.
This feature has been added to avoid problems with hung and
busy backends.
This will increase the network traffic during the normal operation
which could be an issue, but it will lower the
traffic in case some of the cluster nodes are down or busy.
By adding a postfix of ms the delay can be also set in
milliseconds.
|
| receivebuffersize | 0 | Adjusts the size of the explicit (TCP/IP) network buffer size for
proxied connections. This allows you to override the
ProxyReceiveBufferSize for a specific worker.
This must be at least 512 or set to 0 for the system default.
|
| redirect | - | Redirection Route of the worker. This value is usually set dynamically to enable safe removal of the node from the cluster. If set all requests without session id will be redirected to the BalancerMember that has route parametar equal as this value. |
| retry | 60 | Connection pool worker retry timeout in seconds. If the connection pool worker to the backend server is in the error state, Apache httpd will not forward any requests to that server until the timeout expires. This enables to shut down the backend server for maintenance, and bring it back online later. A value of 0 means always retry workers in an error state with no timeout. |
| route | - | Route of the worker when used inside load balancer. The route is a value appended to session id. |
| status | - | Single letter value defining the initial status of this worker: 'D' is disabled, 'S' is stopped, 'I' is ignore-errors, 'H' is hot-standby and 'E' is in an error state. Status can be set (which is the default) by prepending with '+' or cleared by prepending with '-'. Thus, a setting of 'S-E' sets this worker to Stopped and clears the in-error flag. |
| timeout | ProxyTimeout |
Connection timeout in seconds. The number of seconds Apache httpd waits for data sent by / to the backend. |
| ttl | - | Time to live for inactive connections and associated connection
pool entries, in seconds. Those which are unused for at least
ttl seconds will be destroyed.
|
If the Proxy directive scheme starts with the
balancer:// (eg: balancer://cluster/,
any path information is ignored) then a virtual worker that does not really
communicate with the backend server will be created. Instead it is responsible
for the management of several "real" workers. In that case the special set of
parameters can be add to this virtual worker. See mod_proxy_balancer
for more information about how the balancer works.
| Parameter | Default | Description |
|---|---|---|
| lbmethod | byrequests | Balancer load-balance method. Select the load-balancing scheduler
method to use. Either byrequests, to perform weighted
request counting, bytraffic, to perform weighted
traffic byte count balancing, or bybusyness, to perform
pending request balancing. Default is byrequests.
|
| maxattempts | One less than the number of workers, or 1 with a single worker. | Maximum number of failover attempts before giving up. |
| nofailover | Off | If set to On the session will break if the worker is in
error state or disabled. Set this value to On if backend servers do not
support session replication.
|
| stickysession | - | Balancer sticky session name. The value is usually set to something
like JSESSIONID or PHPSESSIONID,
and it depends on the backend application server that support sessions.
If the backend application server uses different name for cookies
and url encoded id (like servlet containers) use | to to separate them.
The first part is for the cookie the second for the path.
|
| scolonpathdelim | Off | If set to On the semi-colon character ';' will be
used as an additional sticky session path deliminator/separator. This
is mainly used to emulate mod_jk's behavior when dealing with paths such
as JSESSIONID=6736bcf34;foo=aabfa
|
| timeout | 0 | Balancer timeout in seconds. If set this will be the maximum time to wait for a free worker. Default is not to wait. |
| failonstatus | - | A single or comma-separated list of HTTP status codes. If set this will force the worker into error state when the backend returns any status code in the list. Worker recovery behaves the same as other worker errors. |
A sample balancer setup
ProxyPass /special-area http://special.example.com smax=5 max=10
ProxyPass / balancer://mycluster/ stickysession=JSESSIONID|jsessionid nofailover=On
<Proxy balancer://mycluster>
BalancerMember ajp://1.2.3.4:8009
BalancerMember ajp://1.2.3.5:8009 loadfactor=20
# Less powerful server, don't send as many requests there,
BalancerMember ajp://1.2.3.6:8009 loadfactor=5
</Proxy>
Setting up a hot-standby, that will only be used if no other members are available
ProxyPass / balancer://hotcluster/
<Proxy balancer://hotcluster>
BalancerMember ajp://1.2.3.4:8009 loadfactor=1
BalancerMember ajp://1.2.3.5:8009 loadfactor=2
# The below is the hot standby
BalancerMember ajp://1.2.3.6:8009 status=+H
ProxySet lbmethod=bytraffic
</Proxy>
Normally, mod_proxy will canonicalise ProxyPassed URLs. But this may be incompatible with some backends, particularly those that make use of PATH_INFO. The optional nocanon keyword suppresses this, and passes the URL path "raw" to the backend. Note that may affect the security of your backend, as it removes the normal limited protection against URL-based attacks provided by the proxy.
The optional interpolate keyword (available in
httpd 2.2.9 and later), in combination with
ProxyPassInterpolateEnv causes the ProxyPass
to interpolate environment variables, using the syntax
${VARNAME}. Note that many of the standard CGI-derived
environment variables will not exist when this interpolation happens,
so you may still have to resort to mod_rewrite
for complex rules.
When used inside a <Location> section, the first argument is omitted and the local
directory is obtained from the <Location>. The same will occur inside a
<LocationMatch> section,
however ProxyPass does not interpret the regexp as such, so it is necessary
to use ProxyPassMatch in this situation instead.
This directive is not supported in <Directory> or <Files> sections.
If you require a more flexible reverse-proxy configuration, see the
RewriteRule directive with the
[P] flag.
| Description: | Enable Environment Variable interpolation in Reverse Proxy configurations |
|---|---|
| Syntax: | ProxyPassInterpolateEnv On|Off |
| Default: | ProxyPassInterpolateEnv Off |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | Available in httpd 2.2.9 and later |
This directive, together with the interpolate argument to
ProxyPass, ProxyPassReverse,
ProxyPassReverseCookieDomain and
ProxyPassReverseCookiePath
enables reverse proxies to be dynamically
configured using environment variables, which may be set by
another module such as mod_rewrite.
It affects the ProxyPass,
ProxyPassReverse,
ProxyPassReverseCookieDomain, and
ProxyPassReverseCookiePath directives,
and causes them to substitute the value of an environment
variable varname for the string ${varname}
in configuration directives.
Keep this turned off (for server performance) unless you need it!
| Description: | Maps remote servers into the local server URL-space using regular expressions |
|---|---|
| Syntax: | ProxyPassMatch [regex] !|url [key=value
[key=value ...]] |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
This directive is equivalent to ProxyPass,
but makes use of regular expressions, instead of simple prefix matching. The
supplied regular expression is matched against the url, and if it
matches, the server will substitute any parenthesized matches into the given
string and use it as a new url.
Suppose the local server has address http://example.com/;
then
ProxyPassMatch ^(/.*\.gif)$ http://backend.example.com$1
will cause a local request for
http://example.com/foo/bar.gif to be internally converted
into a proxy request to http://backend.example.com/foo/bar.gif.
The URL argument must be parsable as a URL before regexp substitutions (as well as after). This limits the matches you can use. For instance, if we had used
ProxyPassMatch ^(/.*\.gif)$ http://backend.example.com:8000$1
in our previous example, it would fail with a syntax error at server startup. This is a bug (PR 46665 in the ASF bugzilla), and the workaround is to reformulate the match:
ProxyPassMatch ^/(.*\.gif)$ http://backend.example.com:8000/$1
The ! directive is useful in situations where you don't want
to reverse-proxy a subdirectory.
When used inside a <LocationMatch> section, the first argument is omitted and the
regexp is obtained from the <LocationMatch>.
If you require a more flexible reverse-proxy configuration, see the
RewriteRule directive with the
[P] flag.
| Description: | Adjusts the URL in HTTP response headers sent from a reverse proxied server |
|---|---|
| Syntax: | ProxyPassReverse [path] url
[interpolate] |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
This directive lets Apache httpd adjust the URL in the Location,
Content-Location and URI headers on HTTP
redirect responses. This is essential when Apache httpd is used as a
reverse proxy (or gateway) to avoid by-passing the reverse proxy
because of HTTP redirects on the backend servers which stay behind
the reverse proxy.
Only the HTTP response headers specifically mentioned above will be rewritten. Apache httpd will not rewrite other response headers, nor will it rewrite URL references inside HTML pages. This means that if the proxied content contains absolute URL references, they will by-pass the proxy. A third-party module that will look inside the HTML and rewrite URL references is Nick Kew's mod_proxy_html.
path is the name of a local virtual path. url is a
partial URL for the remote server - the same way they are used for the
ProxyPass directive.
For example, suppose the local server has address
http://example.com/; then
ProxyPass /mirror/foo/ http://backend.example.com/
ProxyPassReverse /mirror/foo/ http://backend.example.com/
ProxyPassReverseCookieDomain backend.example.com public.example.com
ProxyPassReverseCookiePath / /mirror/foo/
will not only cause a local request for the
http://example.com/mirror/foo/bar to be internally converted
into a proxy request to http://backend.example.com/bar
(the functionality ProxyPass provides here). It also takes care
of redirects the server backend.example.com sends: when
http://backend.example.com/bar is redirected by him to
http://backend.example.com/quux Apache httpd adjusts this to
http://example.com/mirror/foo/quux before forwarding the HTTP
redirect response to the client. Note that the hostname used for
constructing the URL is chosen in respect to the setting of the UseCanonicalName directive.
Note that this ProxyPassReverse directive can
also be used in conjunction with the proxy pass-through feature
(RewriteRule ... [P]) from mod_rewrite
because it doesn't depend on a corresponding ProxyPass directive.
The optional interpolate keyword (available in
httpd 2.2.9 and later), used together with
ProxyPassInterpolateEnv, enables interpolation
of environment variables specified using the format ${VARNAME}.
When used inside a <Location> section, the first argument is omitted and the local
directory is obtained from the <Location>. The same occurs inside a <LocationMatch> section, but will probably not work as
intended, as ProxyPassReverse will interpret the regexp literally as a
path; if needed in this situation, specify the ProxyPassReverse outside
the section, or in a separate <Location> section.
This directive is not supported in <Directory> or <Files> sections.
| Description: | Adjusts the Domain string in Set-Cookie headers from a reverse- proxied server |
|---|---|
| Syntax: | ProxyPassReverseCookieDomain internal-domain
public-domain [interpolate] |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
Usage is basically similar to
ProxyPassReverse, but instead of
rewriting headers that are a URL, this rewrites the domain
string in Set-Cookie headers.
| Description: | Adjusts the Path string in Set-Cookie headers from a reverse- proxied server |
|---|---|
| Syntax: | ProxyPassReverseCookiePath internal-path
public-path [interpolate] |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
Usage is basically similar to
ProxyPassReverse, but instead of
rewriting headers that are a URL, this rewrites the path
string in Set-Cookie headers.
| Description: | Use incoming Host HTTP request header for proxy request |
|---|---|
| Syntax: | ProxyPreserveHost On|Off |
| Default: | ProxyPreserveHost Off |
| Context: | server config, virtual host, directory |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | Available in Apache HTTP Server 2.0.31 and later. Usable in directory context in 2.3.3 and later. |
When enabled, this option will pass the Host: line from the incoming
request to the proxied host, instead of the hostname specified in the
ProxyPass line.
This option should normally be turned Off. It is mostly
useful in special configurations like proxied mass name-based virtual
hosting, where the original Host header needs to be evaluated by the
backend server.
| Description: | Network buffer size for proxied HTTP and FTP connections |
|---|---|
| Syntax: | ProxyReceiveBufferSize bytes |
| Default: | ProxyReceiveBufferSize 0 |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
The ProxyReceiveBufferSize directive specifies an
explicit (TCP/IP) network buffer size for proxied HTTP and FTP connections,
for increased throughput. It has to be greater than 512 or set
to 0 to indicate that the system's default buffer size should
be used.
ProxyReceiveBufferSize 2048
| Description: | Remote proxy used to handle certain requests |
|---|---|
| Syntax: | ProxyRemote match remote-server |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
This defines remote proxies to this proxy. match is either the
name of a URL-scheme that the remote server supports, or a partial URL
for which the remote server should be used, or * to indicate
the server should be contacted for all requests. remote-server is
a partial URL for the remote server. Syntax:
remote-server =
scheme://hostname[:port]
scheme is effectively the protocol that should be used to
communicate with the remote server; only http and https
are supported by this module. When using https, the requests
are forwarded through the remote proxy using the HTTP CONNECT method.
ProxyRemote http://goodguys.example.com/ http://mirrorguys.example.com:8000
ProxyRemote * http://cleverproxy.localdomain
ProxyRemote ftp http://ftpproxy.mydomain:8080
In the last example, the proxy will forward FTP requests, encapsulated as yet another HTTP proxy request, to another proxy which can handle them.
This option also supports reverse proxy configuration - a backend webserver can be embedded within a virtualhost URL space even if that server is hidden by another forward proxy.
| Description: | Remote proxy used to handle requests matched by regular expressions |
|---|---|
| Syntax: | ProxyRemoteMatch regex remote-server |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
The ProxyRemoteMatch is identical to the
ProxyRemote directive, except the
first argument is a regular expression
match against the requested URL.
| Description: | Enables forward (standard) proxy requests |
|---|---|
| Syntax: | ProxyRequests On|Off |
| Default: | ProxyRequests Off |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
This allows or prevents Apache httpd from functioning as a forward proxy
server. (Setting ProxyRequests to Off does not disable use of
the ProxyPass directive.)
In a typical reverse proxy or gateway configuration, this
option should be set to
Off.
In order to get the functionality of proxying HTTP or FTP sites, you
need also mod_proxy_http or mod_proxy_ftp
(or both) present in the server.
Do not enable proxying with ProxyRequests until you have secured your server. Open proxy servers are dangerous
both to your network and to the Internet at large.
| Description: | Set various Proxy balancer or member parameters |
|---|---|
| Syntax: | ProxySet url key=value [key=value ...] |
| Context: | directory |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | ProxySet is only available in Apache HTTP Server 2.2 and later. |
This directive is used as an alternate method of setting any of the
parameters available to Proxy balancers and workers normally done via the
ProxyPass directive. If used
within a <Proxy balancer url|worker url>
container directive, the url argument is not required. As a side
effect the respective balancer or worker gets created. This can be useful
when doing reverse proxying via a
RewriteRule instead of a
ProxyPass directive.
<Proxy balancer://hotcluster>
BalancerMember http://www2.example.com:8080 loadfactor=1
BalancerMember http://www3.example.com:8080 loadfactor=2
ProxySet lbmethod=bytraffic
</Proxy>
<Proxy http://backend>
ProxySet keepalive=On
</Proxy>
ProxySet balancer://foo lbmethod=bytraffic timeout=15
ProxySet ajp://backend:7001 timeout=15
Keep in mind that the same parameter key can have a different meaning depending whether it is applied to a balancer or a worker as shown by the two examples above regarding timeout.
| Description: | Show Proxy LoadBalancer status in mod_status |
|---|---|
| Syntax: | ProxyStatus Off|On|Full |
| Default: | ProxyStatus Off |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | Available in version 2.2 and later |
This directive determines whether or not proxy
loadbalancer status data is displayed via the mod_status
server-status page.
Full is synonymous with On
| Description: | Network timeout for proxied requests |
|---|---|
| Syntax: | ProxyTimeout seconds |
| Default: | Value of |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
| Compatibility: | Available in Apache HTTP Server 2.0.31 and later |
This directive allows a user to specifiy a timeout on proxy requests. This is useful when you have a slow/buggy appserver which hangs, and you would rather just return a timeout and fail gracefully instead of waiting however long it takes the server to return.
| Description: | Information provided in the Via HTTP response
header for proxied requests |
|---|---|
| Syntax: | ProxyVia On|Off|Full|Block |
| Default: | ProxyVia Off |
| Context: | server config, virtual host |
| Status: | Extension |
| Module: | mod_proxy |
This directive controls the use of the Via: HTTP
header by the proxy. Its intended use is to control the flow of
proxy requests along a chain of proxy servers. See RFC 2616 (HTTP/1.1), section
14.45 for an explanation of Via: header lines.
Off, which is the default, no special processing
is performed. If a request or reply contains a Via: header,
it is passed through unchanged.On, each request and reply will get a
Via: header line added for the current host.Full, each generated Via: header
line will additionally have the Apache httpd server version shown as a
Via: comment field.Block, every proxy request will have all its
Via: header lines removed. No new Via: header will
be generated.