mod_proxy - Apache HTTP Server

Apache HTTP Server Version 2.2

Apache > HTTP Server > Documentation > Version 2.2 > Modules

# Apache Module mod_proxy

Available Languages: en | fr | ja

Description: | HTTP/1.1 proxy/gateway server
Status: | Extension
Module Identifier: | proxy_module
Source File: | mod_proxy.c

### Summary

### Warning

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.

This module implements a proxy/gateway for Apache. It implements proxying capability for `AJP13` (Apache JServe Protocol version 1.3), `FTP`, `CONNECT` (for SSL), `HTTP/0.9`, `HTTP/1.0`, and `HTTP/1.1`. The module can be configured to connect to other proxy modules for these and other protocols.

Apache's proxy features are divided into several modules in addition to `mod_proxy`: `mod_proxy_http`, `mod_proxy_ftp`, `mod_proxy_ajp`, `mod_proxy_balancer`, and `mod_proxy_connect`. Thus, if you want to use one or more of the particular proxy functions, load `mod_proxy` and the appropriate module(s) into the server (either statically at compile-time or dynamically via the `LoadModule` directive).

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.

### Directives

### Topics

- 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

### See also

- `mod_cache`
- `mod_proxy_http`
- `mod_proxy_ftp`
- `mod_proxy_connect`
- `mod_proxy_balancer`
- `mod_ssl`

- Comments

## Forward Proxies and Reverse Proxies/Gateways

Apache 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.

## Basic Examples

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`.

### Reverse Proxy

`ProxyPass /foo http://foo.example.com/bar
ProxyPassReverse /foo http://foo.example.com/bar`

### Forward Proxy

`ProxyRequests On
ProxyVia On
<Proxy *>
Order deny,allow
Deny from all
Allow from internal.example.com
</Proxy>`

## Workers

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

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 and some configuration defaults will overwrite the configuration given for the first worker. This will be logged as a warning. In the above example the resulting timeout value for the URL `/apps` will be `10` instead of `60`!

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`, `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`.

## Controlling access to your proxy

You can control who can access your proxy via the `<Proxy>` control block as in the following example:

`<Proxy *>
Order Deny,Allow
Deny from all
Allow from 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.

## Slow Startup

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.

## Intranet Proxy

An Apache 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 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.

## Protocol Adjustments

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>`

## Request Bodies

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.

## Reverse Proxy Request Headers

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-For`
  The IP address of the client.
`X-Forwarded-Host`
  The original host requested by the client in the `Host` HTTP request header.
`X-Forwarded-Server`
  The hostname of the proxy server.

Be 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.

## AllowCONNECT Directive

Description: | Ports that are allowed to `CONNECT` through the proxy
Syntax: | `AllowCONNECT port [port] ...`
Default: | `AllowCONNECT 443 563`
Context: | server config, virtual host
Status: | Extension
Module: | mod_proxy

The `AllowCONNECT` directive specifies a list of port numbers to which the proxy `CONNECT` method may connect. Today's browsers use this method when a `https` connection is requested and proxy tunneling over HTTP is in effect.

By default, only the default https port (`443`) and the default snews port (`563`) are enabled. Use the `AllowCONNECT` directive to override this default and allow connections to the listed ports only.

Note that you'll need to have `mod_proxy_connect` present in the server in order to get the support for the `CONNECT` at all.

## BalancerMember Directive

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 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 pairs available to `ProxyPass` directives.

The balancerurl is only needed when not in `<Proxy balancer://...>` container directive. It corresponds to the url of a balancer defined in `ProxyPass` directive.

## NoProxy 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 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).

### Example

`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:

Domain

  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).

  ### Examples

  `.com .apache.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.

  ### Note

  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.

SubNet

  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 `192.168.0.0`
    the subnet 192.168.0.0 with an implied netmask of 16 valid bits (sometimes used in the netmask form `255.255.0.0`)
  `192.168.112.0/21`
    the subnet `192.168.112.0/21` 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.

IPAddr

  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.

  ### Example

  `192.168.123.7`

  ### Note

  An IPAddr does not need to be resolved by the DNS system, so it can result in more effective apache performance.

Hostname

  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).

  ### Examples

  `prep.ai.example.com
  www.apache.org`

  ### Note

  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 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.

### See also

- DNS Issues

## <Proxy> Directive

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 *>
Order Deny,Allow
Deny from all
Allow from 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>`

### See also

- `<ProxyMatch>`

## ProxyBadHeader Directive

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 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:

`IsError`
  Abort the request and end up with a 502 (Bad Gateway) response. This is the default behaviour.
`Ignore`
  Treat bad header lines as if they weren't sent.
`StartBody`
  When receiving the first bad header line, finish reading the headers and treat the remainder as body. This helps to work around buggy backend servers which forget to insert an empty line between the headers and the body.

## ProxyBlock Directive

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.

### Example

`ProxyBlock joes-garage.com some-host.co.uk rocky.wotsamattau.edu`

`rocky.wotsamattau.edu` would also be matched if referenced by IP address.

Note that `wotsamattau` would also be sufficient to match `wotsamattau.edu`.

Note also that

`ProxyBlock *`

blocks connections to all sites.

## ProxyDomain Directive

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 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.

### Example

`ProxyRemote * http://firewall.example.com:81
NoProxy .example.com 192.168.112.0/21
ProxyDomain .example.com`

## ProxyErrorOverride Directive

Description: | Override error pages for proxied content
Syntax: | `ProxyErrorOverride On|Off`
Default: | `ProxyErrorOverride Off`
Context: | server config, virtual host
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.

## ProxyFtpDirCharset Directive

Description: | Define the character set for proxied FTP listings
Syntax: | `ProxyFtpDirCharset character set`
Default: | `ProxyFtpDirCharset ISO-8859-1`
Context: | server config, virtual host, directory
Status: | Extension
Module: | mod_proxy
Compatibility: | Available in Apache 2.2.7 and later

The `ProxyFtpDirCharset` directive defines the character set to be set for FTP directory listings in HTML generated by `mod_proxy_ftp`.

## ProxyIOBufferSize Directive

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 less or equal `8192`.

In almost every case there's no reason to change that value.

## <ProxyMatch> Directive

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.

### See also

- `<Proxy>`

## ProxyMaxForwards Directive

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 2.0 and later; default behaviour changed in 2.2.7

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.

### Example

`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 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.

## ProxyPass Directive

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.

The `ProxyRequests` directive should usually be set off when using `ProxyPass`.

Suppose the local server has address `http://example.com/`; then

`ProxyPass /mirror/foo/ http://backend.example.com/`

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`.

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.

`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`.

### Ordering ProxyPass Directives

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.

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.

### Example

`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 will return `SERVER_BUSY` status to the client.
connectiontimeout | timeout | Connect timeout in seconds. The number of seconds Apache 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 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'.
keepalive | Off | This parameter should be used when you have a firewall between your Apache and the backend server, who tend to drop inactive connections. This flag will tell the Operating System to send `KEEP_ALIVE` messages on inactive connections and thus prevent the firewall to drop the connection. To enable keepalive set this property value to `On`. 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 webserver to send a `CPING` request on ajp13 connection before forwarding a request. The parameter is the delay in seconds to wait for the `CPONG` reply. This features has been added to avoid problem with hung and busy Tomcat's and require ajp13 ping/pong support which has been implemented on Tomcat 3.3.2+, 4.1.28+ and 5.0.13+. 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. Currently this has an effect only for AJP. By adding a postfix of ms the delay can be also set in milliseconds.
loadfactor | 1 | Worker load factor. Used with BalancerMember. It is a number between 1 and 100 and defines the normalized weighted load applied to the worker.
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 parameter 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 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 waits for data sent by / to the backend.
ttl | - | Time to live for inactive connections and associated connection pool entries, in seconds. Once reaching this limit, a connection will not be used again; it will be closed at some later time.

If the `ProxyPass` 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` (Apache HTTP Server 2.2.10 and later), 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. Available with Apache HTTP Server 2.2.17 and later.
forcerecovery | On | Force the immediate recovery of all workers without considering the retry parameter of the workers if all workers of a balancer are in error state. There might be cases where an already overloaded backend can get into deeper trouble if the recovery of all workers is enforced without considering the retry parameter of each worker. In this case set to `Off`. Available with Apache HTTP Server 2.2.23 and later.

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.

## ProxyPassInterpolateEnv Directive

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 (if the interpolate option is set).

Keep this turned off (for server performance) unless you need it!

## ProxyPassMatch Directive

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
Compatibility: | available in Apache 2.2.5 and later

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`.

### Note

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.

### Security Warning

Take care when constructing the target URL of the rule, considering the security impact from allowing the client influence over the set of URLs to which your server will act as a proxy. Ensure that the scheme and hostname part of the URL is either fixed, or does not allow the client undue influence.

## ProxyPassReverse Directive

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 adjust the URL in the `Location`, `Content-Location` and `URI` headers on HTTP redirect responses. This is essential when Apache 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 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 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.

## ProxyPassReverseCookieDomain Directive

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.

## ProxyPassReverseCookiePath Directive

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

Useful in conjunction with `ProxyPassReverse` in situations where backend URL paths are mapped to public paths on the reverse proxy. This directive rewrites the `path` string in `Set-Cookie` headers. If the beginning of the cookie path matches internal-path, the cookie path will be replaced with public-path.

In the example given with `ProxyPassReverse`, the directive:

`ProxyPassReverseCookiePath / /mirror/foo/`

will rewrite a cookie with backend path `/` (or `/example` or, in fact, anything) to `/mirror/foo/`.

## ProxyPreserveHost Directive

Description: | Use incoming Host HTTP request header for proxy request
Syntax: | `ProxyPreserveHost On|Off`
Default: | `ProxyPreserveHost Off`
Context: | server config, virtual host
Status: | Extension
Module: | mod_proxy
Compatibility: | Available in Apache 2.0.31 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.

## ProxyReceiveBufferSize Directive

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.

### Example

`ProxyReceiveBufferSize 2048`

## ProxyRemote Directive

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.

### Example

`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.

## ProxyRemoteMatch Directive

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.

## ProxyRequests Directive

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 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.

In order to get the functionality of (forward) proxying HTTPS sites, you need `mod_proxy_connect` enabled in the server.

### Warning

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.

### See also

- Forward and Reverse Proxies/Gateways

## ProxySet Directive

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 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`

### Warning

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.

## ProxyStatus Directive

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.

### Note

Full is synonymous with On

## ProxyTimeout Directive

Description: | Network timeout for proxied requests
Syntax: | `ProxyTimeout seconds`
Default: | `Value of `Timeout``
Context: | server config, virtual host
Status: | Extension
Module: | mod_proxy
Compatibility: | Available in Apache 2.0.31 and later

This directive allows a user to specify 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.

## ProxyVia Directive

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.

- If set to `Off`, which is the default, no special processing is performed. If a request or reply contains a `Via:` header, it is passed through unchanged.
- If set to `On`, each request and reply will get a `Via:` header line added for the current host.
- If set to `Full`, each generated `Via:` header line will additionally have the Apache server version shown as a `Via:` comment field.
- If set to `Block`, every proxy request will have all its `Via:` header lines removed. No new `Via:` header will be generated.

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