### Apache HTTP Server Version 2.0

> Warning: This document has been updated to take into account changes made in the 2.0 version of the Apache HTTP Server. Some of the information may still be inaccurate, please use it with care.

# Apache module mod_proxy

This module provides for an HTTP 1.1 proxy / gateway server.

Status: Extension
Source File: mod_proxy.c
Module Identifier: proxy_module
Compatibility: Available in Apache 1.1 and later.

## Summary

This module implements a proxy/gateway for Apache. It implements proxying capability for `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.

This module was experimental in Apache 1.1.x. Improvements and bugfixes were made in Apache v1.2.x and Apache v1.3.x, then the module underwent a major overhaul for Apache v2.0. The protocol support was upgraded to HTTP/1.1, and filter support was enabled.

Please note that the caching function present in mod_proxy up to Apache v1.3.x has been removed from mod_proxy and will be incorporated into a new module, mod_cache.

## Directives

- ProxyRequests
- ProxyRemote
- ProxyPass
- ProxyPassReverse
- ProxyBlock
- AllowCONNECT
- ProxyReceiveBufferSize
- ProxyMaxForwards
- NoProxy
- ProxyDomain
- ProxyVia
- ProxyErrorOverride

## Common configuration topics

- Forward and Reverse Proxies
- Controlling access to your proxy
- Using Netscape hostname shortcuts
- Why doesn't file type xxx download via FTP?
- Why does Apache start more slowly when using the proxy module?
- What other functions are useful for an intranet proxy server?

## Forward and Reverse Proxies

Apache can be configured in both a forward and reverse proxy configuration.

A forward proxy is an intermediate system that enables a browser to connect to a remote network to which it normally does not have access. A forward proxy can also be used to cache data, reducing load on the networks between the forward proxy and the remote webserver.

Apache's mod_proxy can be figured to behave like a forward proxy using the ProxyRemote directive. In addition, caching of data can be achieved by configuring Apache mod_cache. Other dedicated forward proxy packages include Squid.

A reverse proxy is a webserver system that is capable of serving webpages sourced from other webservers - in addition to webpages on disk or generated dynamically by CGI - making these pages look like they originated at the reverse proxy.

When configured with the mod_cache module the reverse proxy can act as a cache for slower backend webservers. The reverse proxy can also enable advanced URL strategies and management techniques, allowing webpages served using different webserver systems or architectures to coexist inside the same URL space. Reverse proxy systems are also ideal for implementing centralised logging websites with many or diverse website backends. Complex multi-tier webserver systems can be constructed using an Apache mod_proxy frontend and any number of backend webservers.

The reverse proxy is configured using the ProxyPass and ProxyPassReverse directives. Caching can be enabled using mod_cache as with the forward proxy.

## Controlling access to your proxy

You can control who can access your proxy via the normal <Directory> control block using the following example:

    <Directory proxy:*>
    Order Deny,Allow
    Deny from [machines you'd like *not* to allow by IP address or name]
    Allow from [machines you'd like to allow by IP address or name]
    </Directory>

A <Files> block will also work, and is the only method known to work for all possible URLs in Apache versions earlier than 1.2b10.

When configuring a reverse proxy, access control takes on the attributes of the normal server configuration.

## Why doesn't file type xxx download via FTP?

You probably don't have that particular file type defined as application/octet-stream in your proxy's mime.types configuration file. A useful line can be

    application/octet-stream        bin dms lha lzh exe class tgz taz

## How can I force an FTP ASCII download of File xxx?

In the rare situation where you must download a specific file using the FTP ASCII transfer method (while the default transfer is in binary mode), you can override mod_proxy's default by suffixing the request with `;type=a` to force an ASCII transfer.

## Why does Apache start more slowly when using the proxy module?

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.

## What other functions are useful for an intranet proxy server?

An Apache proxy server situated in an intranet needs to forward external requests through the company's firewall. 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.my.dom.ain/". 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.

## ProxyRequests directive

Syntax: ProxyRequests on|off
Default: `ProxyRequests Off`
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyRequests is only available in Apache 1.1 and later.

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 configuration, this option should be set to 'off'.

## ProxyRemote directive

Syntax: ProxyRemote match remote-server
Default: None
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyRemote is only available in Apache 1.1 and later.

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 = protocol://hostname[:port]

protocol is the protocol that should be used to communicate with the remote server; only "http" is supported by this module.

Example:

      ProxyRemote http://goodguys.com/ http://mirrorguys.com:8000
      ProxyRemote * http://cleversite.com
      ProxyRemote ftp http://ftpproxy.mydomain.com: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.

## ProxyPass directive

Syntax: ProxyPass path url
or: ProxyPass url when placed in a <location> directive (Apache 2.0 only)
Default: None
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyPass is only available in Apache 1.1 and later.

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. path is the name of a local virtual path; url is a partial URL for the remote server.

Suppose the local server has address `http://wibble.org/`; then

       ProxyPass /mirror/foo/ http://foo.com/

will cause a local request for the <`http://wibble.org/mirror/foo/bar`> to be internally converted into a proxy request to <`http://foo.com/bar`>.

## ProxyPassReverse directive

Syntax: ProxyPassReverse path url
or: ProxyPassReverse url when placed in a <location> directive (Apache 2.0 only)
Default: None
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyPassReverse is only available in Apache 1.3b6 and later.

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 to avoid by-passing the reverse proxy because of HTTP redirects on the backend servers which stay behind the reverse proxy.

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.

Example:
Suppose the local server has address `http://wibble.org/`; then

       ProxyPass         /mirror/foo/ http://foo.com/
       ProxyPassReverse  /mirror/foo/ http://foo.com/

will not only cause a local request for the <`http://wibble.org/mirror/foo/bar`> to be internally converted into a proxy request to <`http://foo.com/bar`> (the functionality `ProxyPass` provides here). It also takes care of redirects the server foo.com sends: when `http://foo.com/bar` is redirected by him to `http://foo.com/quux` Apache adjusts this to `http://wibble.org/mirror/foo/quux` before forwarding the HTTP redirect response to the client.

Note that this `ProxyPassReverse` directive can also be used in conjunction with the proxy pass-through feature ("`RewriteRule ... [P]`") from `mod_rewrite` because its doesn't depend on a corresponding `ProxyPass` directive.

## AllowCONNECT directive

Syntax: AllowCONNECT port [port] ...
Default: `AllowCONNECT` 443 563
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: `AllowCONNECT` is only available in Apache 1.3.2 and later.

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 overrride this default and allow connections to the listed ports only.

## ProxyBlock directive

Syntax: ProxyBlock *|word|host|domain [word|host|domain] ...
Default: None
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyBlock is only available in Apache 1.2 and later.

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. 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.

## ProxyReceiveBufferSize directive

Syntax: ProxyReceiveBufferSize bytes
Default: None
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyReceiveBufferSize is only available in Apache 1.3 and later.

The ProxyReceiveBufferSize directive specifies an explicit network buffer size for outgoing 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

## ProxyMaxForwards directive

Syntax: ProxyMaxForwards bytes
Default: 10
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyMaxForwards is only available in Apache 2.0 and later.

The ProxyMaxForwards directive specifies the maximum number of proxies through which a request may pass. This is set to prevent infinite proxy loops, or a DoS attack.

Example:

      ProxyMaxForwards 10

## NoProxy directive

Syntax: NoProxy Domain|SubNet|IpAddr|Hostname [Domain|SubNet|IpAddr|Hostname] ...
Default: None
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: NoProxy is only available in Apache 1.3 and later.

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.mycompany.com:81
      NoProxy         .mycompany.com 192.168.112.0/21

The 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 `.MyDomain.com` and `.mydomain.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.

  See Also: DNS Issues

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 IPAddr's).
  Examples: `prep.ai.mit.edu` `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.
  Note: 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.MyDomain.com` and `www.mydomain.com.` (note the trailing period) are considered equal.

  See Also: DNS Issues

## ProxyDomain directive

Syntax: ProxyDomain Domain
Default: None
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyDomain is only available in Apache 1.3 and later.

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.mycompany.com:81
      NoProxy         .mycompany.com 192.168.112.0/21
      ProxyDomain     .mycompany.com

## ProxyVia directive

Syntax: ProxyVia on|off|full|block
Default: ProxyVia off
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyVia is only available in Apache 1.3.2 and later.

This directive controls the use of the `Via:` HTTP header by the proxy. Its intended use is to control the flow of of proxy requests along a chain of proxy servers. See RFC2068 (HTTP/1.1) 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.

## ProxyErrorOverride directive

Syntax: ProxyErrorOverrideon
Default: off
Context: server config, virtual host
Override: Not applicable
Status: Base
Module: mod_proxy
Compatibility: ProxyErrorOverride Apache 2.0 and later.

This directive is usefull for reverse-proxy setups, where you wan't 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 )

### Apache HTTP Server Version 2.0