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Apache Module mod_proxy

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Description:Multi-protocol proxy/gateway server
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:

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.

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See also


Forward Proxies and Reverse Proxies/Gateways

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. 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 namespace of the reverse proxy. The reverse proxy then decides where to send those requests and returns the content as if it were 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 "*">
  Require host internal.example.com

Access via Handler

You can also force a request to be handled as a reverse-proxy request, by creating a suitable Handler pass-through. The example configuration below will pass all requests for PHP scripts to the specified FastCGI server using reverse proxy:

Reverse Proxy PHP scripts

<FilesMatch "\.php$">
    # Unix sockets require 2.4.7 or later
    SetHandler  "proxy:unix:/path/to/app.sock|fcgi://localhost/"

This feature is available in Apache HTTP Server 2.4.10 and later.



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 reuse. 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 that will use 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

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 also be 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 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.

DNS resolution for origin domains

DNS resolution happens when the socket to the origin domain is created for the first time. When connection reuse is enabled, each backend domain is resolved only once per child process, and cached for all further connections until the child is recycled. This information should to be considered while planning DNS maintenance tasks involving backend domains. Please also check ProxyPass parameters for more details about connection reuse.


Controlling Access to Your Proxy

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

<Proxy "*">
  Require ip 192.168.0

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.


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 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.


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

In 2.4.26 and later, the "no-proxy" environment variable can be set to disable mod_proxy processing the current request. This variable should be set with SetEnvIf, as SetEnv is not evaluated early enough.


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.

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


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:

The IP address of the client.
The original host requested by the client in the Host HTTP request header.
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.

Note: If you need to specify custom request headers to be added to the forwarded request, use the RequestHeader directive.


BalancerGrowth Directive

Description:Number of additional Balancers that can be added Post-configuration
Syntax:BalancerGrowth #
Default:BalancerGrowth 5
Context:server config, virtual host
Compatibility:BalancerGrowth is only available in Apache HTTP Server 2.3.13 and later.

This directive allows for growth potential in the number of Balancers available for a virtualhost in addition to the number pre-configured. It only takes effect if there is at least one pre-configured Balancer.


BalancerInherit Directive

Description:Inherit ProxyPassed Balancers/Workers from the main server
Syntax:BalancerInherit On|Off
Default:BalancerInherit On
Context:server config, virtual host
Compatibility:BalancerInherit is only available in Apache HTTP Server 2.4.5 and later.

This directive will cause the current server/vhost to "inherit" ProxyPass Balancers and Workers defined in the main server. This can cause issues and inconsistent behavior if using the Balancer Manager and so should be disabled if using that feature.

The setting in the global server defines the default for all vhosts.


BalancerMember Directive

Description:Add a member to a load balancing group
Syntax:BalancerMember [balancerurl] url [key=value [key=value ...]]
Compatibility:BalancerMember is only available in Apache HTTP Server 2.2 and later.

This directive adds a member to a load balancing group. It can 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 decimal number between 1.0 (default) and 100.0, which defines the weighted load to be applied to the member in question.

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

The path component of the balancer URL in any <Proxy balancer://...> container directive is ignored.

Trailing slashes should typically be removed from the URL of a BalancerMember.


BalancerPersist Directive

Description:Attempt to persist changes made by the Balancer Manager across restarts.
Syntax:BalancerPersist On|Off
Default:BalancerPersist Off
Context:server config, virtual host
Compatibility:BalancerPersist is only available in Apache HTTP Server 2.4.4 and later.

This directive will cause the shared memory storage associated with the balancers and balancer members to be persisted across restarts. This allows these local changes to not be lost during the normal restart/graceful state transitions.


NoProxy Directive

Description:Hosts, domains, or networks that will be connected to directly
Syntax:NoProxy host [host] ...
Context:server config, virtual host

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" ""

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, the 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
the subnet with an implied netmask of 16 valid bits (sometimes used in the netmask form
the subnet with a netmask of 21 valid bits (also used in the form

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., 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.



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).




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, the two hosts WWW.ExAmple.com and www.example.com. (note the trailing period) are considered equal.

See also


<Proxy> Directive

Description:Container for directives applied to proxied resources
Syntax:<Proxy wildcard-url> ...</Proxy>
Context:server config, virtual host

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

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

Differences from the Location configuration section

A backend URL matches the configuration section if it begins with the the wildcard-url string, even if the last path segment in the directive only matches a prefix of the backend URL. For example, <Proxy "http://example.com/foo"> matches all of http://example.com/foo, http://example.com/foo/bar, and http://example.com/foobar. The matching of the final URL differs from the behavior of the <Location> section, which for purposes of this note treats the final path component as if it ended in a slash.

For more control over the matching, see <ProxyMatch>.

See also


ProxyAddHeaders Directive

Description:Add proxy information in X-Forwarded-* headers
Syntax:ProxyAddHeaders Off|On
Default:ProxyAddHeaders On
Context:server config, virtual host, directory
Compatibility:Available in version 2.3.10 and later

This directive determines whether or not proxy related information should be passed to the backend server through X-Forwarded-For, X-Forwarded-Host and X-Forwarded-Server HTTP headers.


This option is of use only for HTTP proxying, as handled by mod_proxy_http.


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

The ProxyBadHeader directive determines the behavior 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:

Abort the request and end up with a 502 (Bad Gateway) response. This is the default behavior.
Treat bad header lines as if they weren't sent.
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

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.


ProxyDomain Directive

Description:Default domain name for proxied requests
Syntax:ProxyDomain Domain
Context:server config, virtual host

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" ""
ProxyDomain     ".example.com"

ProxyErrorOverride Directive

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

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.


ProxyIOBufferSize Directive

Description:Determine size of internal data throughput buffer
Syntax:ProxyIOBufferSize bytes
Default:ProxyIOBufferSize 8192
Context:server config, virtual host

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. Values larger than 65536 are set to 65536. 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.


<ProxyMatch> Directive

Description:Container for directives applied to regular-expression-matched proxied resources
Syntax:<ProxyMatch regex> ...</ProxyMatch>
Context:server config, virtual host

The <ProxyMatch> directive is identical to the <Proxy> directive, except that it matches URLs using regular expressions.

From 2.4.8 onwards, named groups and backreferences are captured and written to the environment with the corresponding name prefixed with "MATCH_" and in upper case. This allows elements of URLs to be referenced from within expressions and modules like mod_rewrite. In order to prevent confusion, numbered (unnamed) backreferences are ignored. Use named groups instead.

<ProxyMatch "^http://(?<sitename>[^/]+)">
    Require ldap-group cn=%{env:MATCH_SITENAME},ou=combined,o=Example

See also


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
Compatibility: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.


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 behavior 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] [noquery]
Context:server config, virtual host, directory
Compatibility:Unix Domain Socket (UDS) support added in 2.4.7

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.

It is strongly suggested to review the concept of a Worker before proceed