Apache Module mod_proxy

Summary

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 theLoadModule directive). The set must include:

• mod_proxy, which provides basic proxy capabilities
• mod_proxy_balancer and one or more balancer modules if load balancing is required. (Seemod_proxy_balancer for more information.)
• one or more proxy scheme, or protocol, modules:

  Protocol	Module
  AJP13 (Apache JServe Protocol version 1.3)	mod_proxy_ajp
  CONNECT (for SSL)	mod_proxy_connect
  FastCGI	mod_proxy_fcgi
  ftp	mod_proxy_ftp
  HTTP/0.9, HTTP/1.0, and HTTP/1.1	mod_proxy_http
  HTTP/2.0	mod_proxy_http2
  SCGI	mod_proxy_scgi
  UWSGI	mod_proxy_uwsgi
  WS and WSS (Web-sockets)	mod_proxy_wstunnel

In addition, extended features are provided by other modules. Caching is provided bymod_cache and related modules. The ability to contact remote servers using the SSL/TLS protocol is provided by theSSLProxy* directives ofmod_ssl. These additional modules will need to be loaded and configured to take advantage of these features.

Topics

• Forward Proxies and Reverse Proxies/Gateways
• Basic Examples
• Access via Handler
• Workers
• Controlling Access to Your Proxy
• Slow Startup
• Intranet Proxy
• Protocol Adjustments
• Request Bodies
• Reverse Proxy Request Headers

Directives

• BalancerGrowth
• BalancerInherit
• BalancerMember
• BalancerPersist
• NoProxy
• <Proxy>
• Proxy100Continue
• ProxyAddHeaders
• ProxyBadHeader
• ProxyBlock
• ProxyDomain
• ProxyErrorOverride
• ProxyIOBufferSize
• <ProxyMatch>
• ProxyMaxForwards
• ProxyPass
• ProxyPassInherit
• ProxyPassInterpolateEnv
• ProxyPassMatch
• ProxyPassReverse
• ProxyPassReverseCookieDomain
• ProxyPassReverseCookiePath
• ProxyPreserveHost
• ProxyReceiveBufferSize
• ProxyRemote
• ProxyRemoteMatch
• ProxyRequests
• ProxySet
• ProxySourceAddress
• ProxyStatus
• ProxyTimeout
• ProxyVia

Bugfix checklist

• httpd changelog
• Known issues
• Report a bug

See also

• mod_cache
• mod_proxy_ajp
• mod_proxy_balancer
• mod_proxy_connect
• mod_proxy_fcgi
• mod_proxy_ftp
• mod_proxy_hcheck
• mod_proxy_http
• mod_proxy_scgi
• mod_proxy_wstunnel
• mod_ssl
• Comments

Forward Proxies and Reverse Proxies/Gateways

Apache HTTP Server can be configured in both aforward andreverse proxy (also known asgateway) mode.

An ordinaryforward proxy is an intermediate server that sits between the client and theorigin 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 bymod_cache) to reduce network usage.

The forward proxy is activated using theProxyRequests directive. Because forward proxies allow clients to access arbitrary sites through your server and to hide their true origin, it is essential that yousecure your server so that only authorized clients can access the proxy before activating a forward proxy.

Areverse proxy (orgateway), 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 theProxyPass directive or the[P] flag to theRewriteRule directive. It isnot necessary to turnProxyRequests 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 frommod_cache.

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

ProxyRequests OnProxyVia On<Proxy "*">  Require host internal.example.com</Proxy>

ProxyPass "/some/ws/capable/path/" "http://example.com/some/ws/capable/path/" upgrade=websocket

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:

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

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

Workers

The proxy manages the configuration of origin servers and their communication parameters in objects calledworkers. 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 usingProxyPass orProxyPassMatch 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 URLhttp://backend.example.com that will use the given timeout values. When used in a forward proxy, workers are usually defined via theProxySet directive:

ProxySet "http://backend.example.com" connectiontimeout=5 timeout=30

or alternatively usingProxy andProxySet:

<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 byProxyPass 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.

ProxyPass "/apps" "http://backend.example.com/" timeout=60ProxyPass "/examples" "http://backend.example.com/examples" timeout=10

Explicitly configured workers come in two flavors:direct workers and(load) balancer workers. They support many important configuration attributes which are described below in theProxyPass directive. The same attributes can also be set usingProxySet.

The set of options available for a direct worker depends on the protocol which is specified in the origin server URL. Available protocols includeajp,fcgi,ftp,http andscgi.

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 usesbalancer as the protocol scheme. The balancer URL uniquely identifies the balancer worker. Members are added to a balancer usingBalancerMember.

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</Proxy>

For more information on access control directives, seemod_authz_host.

Strictly limiting access is essential if you are using a forward proxy (using theProxyRequests 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 theProxyPass directive withProxyRequests Off), access control is less critical because clients can only contact the hosts that you have specifically configured.

See Also theProxy-Chain-Auth environment variable.

Slow Startup

If you're using theProxyBlock 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 theProxyRemote directive to forward the respectivescheme to the firewall proxy). However, when it has to access resources within the intranet, it can bypass the firewall when accessing hosts. TheNoProxy 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 ofhttp://somehost.example.com/. Some commercial proxy servers let them get away with this and simply serve the request, implying a configured local domain. When theProxyDomain directive is used and the server isconfigured 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 wheremod_proxy is sending requests to an origin server that doesn't properly implement keepalives or HTTP/1.1, there are twoenvironment variables that can force the request to use HTTP/1.0 with no keepalive. These are set via theSetEnv directive.

These are theforce-proxy-request-1.0 andproxy-nokeepalive notes.

<Location "/buggyappserver/">  ProxyPass "http://buggyappserver:7001/foo/"  SetEnv force-proxy-request-1.0 1  SetEnv proxy-nokeepalive 1</Location>

In 2.4.26 and later, the "no-proxy" environment variable can be set to disablemod_proxy processing the current request. This variable should be set withSetEnvIf, asSetEnv 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 aContent-Length request header. When passing these requests on to the origin server,mod_proxy_http will always attempt to send theContent-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 usingenvironment variables. Settingproxy-sendcl ensures maximum compatibility with upstream servers by always sending theContent-Length, while settingproxy-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.

Reverse Proxy Request Headers

When acting in a reverse-proxy mode (using theProxyPass 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 theHost 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 theProxyPreserveHost andProxyVia directives, which control other request headers.

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

BalancerGrowthDirective

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.

BalancerInheritDirective

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.

BalancerMemberDirective

This directive adds a member to a load balancing group. It can be used within a<Proxybalancer://...> container directive and can take any of the key value pair parameters available toProxyPass directives.

One additional parameter is available only toBalancerMember 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.

Thebalancerurl is only needed when not within a<Proxybalancer://...> container directive. It corresponds to the url of a balancer defined inProxyPass directive.

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

Trailing slashes should typically be removed from the URL of aBalancerMember.

BalancerPersistDirective

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.

NoProxyDirective

This directive is only useful for Apache httpd proxy servers within intranets. TheNoProxy 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 configuredProxyRemote proxy server(s).

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

Thehost arguments to theNoProxy directive are one of the following type list:

Domain

ADomain 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 inDomain).

Examples

.com .example.org.

To distinguishDomains fromHostnames (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, andDomains 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.

SubNet

ASubNet 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 theSubNet. 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 or192.168.0.0

the subnet 192.168.0.0 with an implied netmask of 16 valid bits (sometimes used in the netmask form255.255.0.0)

192.168.112.0/21

the subnet192.168.112.0/21 with a netmask of 21 valid bits (also used in the form255.255.248.0)

As a degenerate case, aSubNet with 32 valid bits is the equivalent to anIPAddr, while aSubNet with zero valid bits (e.g., 0.0.0.0/0) is the same as the constant_Default_, matching any IP address.

IPAddr

AIPAddr 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

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

Hostname

AHostname is a fully qualified DNS domain name which can be resolved to one or moreIPAddrs via the DNS domain name service. It represents a logical host (in contrast toDomains, see above) and must be resolvable to at least oneIPAddr (or often to a list of hosts with differentIPAddrs).

Examples

prep.ai.example.edu
www.example.org

Note

In many situations, it is more effective to specify anIPAddr in place of aHostname 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, andHostnames are always assumed to be anchored in the root of the DNS tree; therefore, the two hostsWWW.ExAmple.com andwww.example.com. (note the trailing period) are considered equal.

See also

• DNS Issues

<Proxy>Directive

Directives placed in<Proxy> sections apply only to matching proxied content. Shell-style wildcards are allowed.

For example, the following will allow only hosts inyournetwork.example.com to access content via your proxy server:

<Proxy "*">  Require host yournetwork.example.com</Proxy>

The following example will process all files in thefoo directory ofexample.com through theINCLUDES filter when they are sent through the proxy server:

<Proxy "http://example.com/foo/*">  SetOutputFilter INCLUDES</Proxy>

See also

• <ProxyMatch>

Proxy100ContinueDirective

This directive determines whether the proxy should forward 100-continueExpect:ation to the origin server and thus let it decide when/if the HTTP request body should be read, or whenOff the proxy should generate100 Continue intermediate response by itself before forwarding the request body.

ProxyAddHeadersDirective

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.

ProxyBadHeaderDirective

TheProxyBadHeader directive determines the behavior ofmod_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 behavior.

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.

ProxyBlockDirective

TheProxyBlock 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 areblocked 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 thatexample 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.

ProxyDomainDirective

This directive is only useful for Apache httpd proxy servers within intranets. TheProxyDomain 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 configuredDomain appended will be generated.

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

ProxyErrorOverrideDirective

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 (viamod_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.

By defaultProxyErrorOverride affects all responses with codes between 400 (including) and 600 (excluding).

ProxyErrorOverride  On

To change the default behavior, you can specify the status codes to consider, separated by spaces. If you do so, all other status codes will be ignored. You can only specify status codes, that are considered error codes: between 400 (including) and 600 (excluding).

ProxyErrorOverride  On 403 405 500 501 502 503 504

ProxyIOBufferSizeDirective

TheProxyIOBufferSize 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 least512.

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 thepacketSize attribute of your AJP connector on the Tomcat side! The attributepacketSize is only available in Tomcat5.5.20+ and6.0.2+

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

The<ProxyMatch> directive is identical to the<Proxy> directive, except that it matches URLs usingregular 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 withinexpressions and modules likemod_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</ProxyMatch>

See also

• <Proxy>

ProxyMaxForwardsDirective

TheProxyMaxForwards directive specifies the maximum number of proxies through which a request may pass if there's noMax-Forwards header supplied with the request. This may be set to prevent infinite proxy loops or a DoS attack.

ProxyMaxForwards 15

Note that settingProxyMaxForwards is a violation of the HTTP/1.1 protocol (RFC2616), which forbids a Proxy settingMax-Forwards if the Client didn't set it. Earlier Apache httpd versions would always set it. A negativeProxyMaxForwards value, including the default -1, gives you protocol-compliant behavior but may leave you open to loops.

ProxyPassDirective

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 areverse proxy orgateway. Thepath is the name of a local virtual path;url is a partial URL for the remote server and cannot include a query string.

In 2.4.7 and later, support for using a Unix Domain Socket is available by using a target which prependsunix:/path/lis.sock|. For example, to proxy HTTP and target the UDS at /home/www.socket, you would useunix:/home/www.socket|http://localhost/whatever/.

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 useProxyPassMatch in this situation instead.

Suppose the local server has addresshttp://example.com/; then

<Location "/mirror/foo/">    ProxyPass "http://backend.example.com/"</Location>

will cause a local request forhttp://example.com/mirror/foo/bar to be internally converted into a proxy request tohttp://backend.example.com/bar.

If you require a more flexible reverse-proxy configuration, see theRewriteRule directive with the[P] flag.

The following alternative syntax is possible; however, it can carry a performance penalty when present in very large numbers. The advantage of the below syntax is that it allows for dynamic control via theBalancer Manager interface:

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

The! directive is useful in situations where you don't want to reverse-proxy a subdirectory,e.g.

<Location "/mirror/foo/">    ProxyPass "http://backend.example.com/"</Location><Location "/mirror/foo/i">    ProxyPass "!"</Location>

ProxyPass "/mirror/foo/i" "!"ProxyPass "/mirror/foo" "http://backend.example.com"

will proxy all requests to/mirror/foo tobackend.example.comexcept requests made to/mirror/foo/i.

Mixing ProxyPass settings in different contexts does not work:

ProxyPass "/mirror/foo/i" "!"<Location "/mirror/foo/">    ProxyPass "http://backend.example.com/"</Location>

In this case, a request to/mirror/foo/i will get proxied, because theProxyPass directive in the Location block will be evaluated first. The fact thatProxyPass supports both server and directory contexts does not mean that their scope and position in the configuration file will guarantee any ordering or override.

ProxyPasskey=value Parameters

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 theProxyPass directive usingkey=value parameters, described in the tables below.

Use thettl parameter to set an optional time to live; connections which have been unused for at leastttl 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.

ProxyPass "/example" "http://backend.example.com" max=20 ttl=120 retry=300

ProxyPass "/special%3Fsegment" "https://example.com/special%3Fsegment" mapping=encoded

<Location "/special%3Fsegment">  Require ip 172.17.2.0/24</Location>

ProxyPass "/some/path" "https://servlet.example.com/some/path" mapping=servlet

<Location "/some/path">  Require valid-user</Location>

If the Proxy directive scheme starts with thebalancer:// (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 added to this virtual worker. Seemod_proxy_balancer for more information about how the balancer works.

A sample balancer setup:

ProxyPass "/special-area" "http://special.example.com" smax=5 max=10ProxyPass "/" "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>

Configuring hot spares can help ensure that a certain number of workers are always available for use per load balancer set:

ProxyPass "/" "balancer://sparecluster/"<Proxy balancer://sparecluster>    BalancerMember ajp://1.2.3.4:8009    BalancerMember ajp://1.2.3.5:8009    # The servers below are hot spares. For each server above that is unusable    # (draining, stopped, unreachable, in error state, etc.), one of these spares    # will be used in its place. Two servers will always be available for a request    # unless one or more of the spares is also unusable.    BalancerMember ajp://1.2.3.6:8009 status=+R    BalancerMember ajp://1.2.3.7:8009 status=+R</Proxy>

Setting up a hot-standby that will only be used if no other members (or spares) are available in the load balancer set:

ProxyPass "/" "balancer://hotcluster/"<Proxy "balancer://hotcluster">    BalancerMember "ajp://1.2.3.4:8009" loadfactor=1    BalancerMember "ajp://1.2.3.5:8009" loadfactor=2.25    # The server below is on hot standby    BalancerMember "ajp://1.2.3.6:8009" status=+H    ProxySet lbmethod=bytraffic</Proxy>

Additional ProxyPass Keywords

Normally, mod_proxy will canonicalise ProxyPassed URLs. But this may be incompatible with some backends, particularly those that make use ofPATH_INFO. The optionalnocanon keyword suppresses this and passes the URL path "raw" to the backend. Note that this keyword may affect the security of your backend, as it removes the normal limited protection against URL-based attacks provided by the proxy.

Normally, mod_proxy will include the query string when generating theSCRIPT_FILENAME environment variable. The optionalnoquery keyword (available in httpd 2.4.1 and later) prevents this.

The optionalinterpolate keyword, in combination withProxyPassInterpolateEnv, 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 tomod_rewrite for complex rules. Also note that interpolation is supported within the scheme/hostname/port portion of a URL only for variables that are available when the directive is parsed (likeDefine). Dynamic determination of those fields can be accomplished withmod_rewrite. The following example describes how to usemod_rewrite to dynamically set the scheme to http or https:

RewriteEngine OnRewriteCond "%{HTTPS}" =offRewriteRule "." "-" [E=protocol:http]RewriteCond "%{HTTPS}" =onRewriteRule "." "-" [E=protocol:https]RewriteRule "^/mirror/foo/(.*)" "%{ENV:protocol}://backend.example.com/$1" [P]ProxyPassReverse  "/mirror/foo/" "http://backend.example.com/"ProxyPassReverse  "/mirror/foo/" "https://backend.example.com/"

ProxyPassInheritDirective

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

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

Disabling ProxyPassInherit also disablesBalancerInherit.

ProxyPassInterpolateEnvDirective

This directive, together with theinterpolate argument toProxyPass,ProxyPassReverse,ProxyPassReverseCookieDomain, andProxyPassReverseCookiePath, enables reverse proxies to be dynamically configured using environment variables which may be set by another module such asmod_rewrite. It affects theProxyPass,ProxyPassReverse,ProxyPassReverseCookieDomain, andProxyPassReverseCookiePath directives and causes them to substitute the value of an environment variablevarname for the string${varname} in configuration directives if theinterpolate option is set.

The scheme/hostname/port portion ofProxyPass may contain variables, but only the ones available when the directive is parsed (for example, usingDefine). For all the other use cases, please consider usingmod_rewrite instead.

ProxyPassMatchDirective

This directive is equivalent toProxyPass but makes use of regular expressions instead of simple prefix matching. The supplied regular expression is matched against theurl, and if it matches, the server will substitute any parenthesized matches into the given string and use it as a newurl.

Suppose the local server has addresshttp://example.com/; then

ProxyPassMatch "^/(.*\.gif)$" "http://backend.example.com/$1"

will cause a local request forhttp://example.com/foo/bar.gif to be internally converted into a proxy request tohttp://backend.example.com/foo/bar.gif.

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 theRewriteRule directive with the[P] flag.

ProxyPassReverseDirective

This directive lets Apache httpd adjust the URL in theLocation,Content-Location andURI headers on HTTP redirect responses. This is essential when Apache httpd is used as a reverse proxy (or gateway) to avoid bypassing the reverse proxy because of HTTP redirects on the backend servers which stay behind the reverse proxy.

Only the HTTP response headers specifically mentioned above will be rewritten. Apache httpd will not rewrite other response headers, nor will it by default rewrite URL references inside HTML pages. This means that if the proxied content contains absolute URL references, they will bypass the proxy. To rewrite HTML content to match the proxy, you must load and enablemod_proxy_html.

path is the name of a local virtual path;url is a partial URL for the remote server. These parameters are used the same way as for theProxyPass directive.

For example, suppose the local server has addresshttp://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 thehttp://example.com/mirror/foo/bar to be internally converted into a proxy request tohttp://backend.example.com/bar (the functionality whichProxyPass provides here). It also takes care of redirects which the serverbackend.example.com sends when redirectinghttp://backend.example.com/bar tohttp://backend.example.com/quux . Apache httpd adjusts this tohttp://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 theUseCanonicalName directive.

Note that thisProxyPassReverse directive can also be used in conjunction with the proxy feature (RewriteRule ... [P]) frommod_rewrite because it doesn't depend on a correspondingProxyPass directive.

The optionalinterpolate keyword, used together withProxyPassInterpolateEnv, enables interpolation of environment variables specified using the format${VARNAME}. Note that interpolation is not supported within the scheme portion of a URL.

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.

ProxyPassReverseCookieDomainDirective

Usage is basically similar toProxyPassReverse, but instead ofrewriting headers that are a URL, this rewrites thedomainstring inSet-Cookie headers.

ProxyPassReverseCookiePathDirective

Useful in conjunction withProxyPassReversein situations where backend URL paths are mapped to public paths on thereverse proxy. This directive rewrites thepath string inSet-Cookie headers. If the beginning of the cookie path matchesinternal-path, the cookie path will be replaced withpublic-path.

In the example given withProxyPassReverse, the directive:

ProxyPassReverseCookiePath  "/"  "/mirror/foo/"

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

ProxyPreserveHostDirective

When enabled, this option will pass theHost: line from the incoming request to the proxied host, instead of the hostname specified in theProxyPass line.

This option should normally be turnedOff. 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.

ProxyReceiveBufferSizeDirective

TheProxyReceiveBufferSize directive specifies an explicit (TCP/IP) network buffer size for proxied HTTP and FTP connections, for increased throughput. It has to be greater than512 or set to0 to indicate that the system's default buffer size should be used.

ProxyReceiveBufferSize 2048

ProxyRemoteDirective

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:

scheme is effectively the protocol that should be used to communicate with the remote server; onlyhttp andhttps are supported by this module. When usinghttps, the requests are forwarded through the remote proxy using the HTTP CONNECT method.

ProxyRemote "http://goodguys.example.com/" "http://mirrorguys.example.com:8000"ProxyRemote "*" "http://cleverproxy.localdomain"ProxyRemote "ftp" "http://ftpproxy.mydomain:8080"

In the last example, the proxy will forward FTP requests, encapsulated as yet another HTTP proxy request, to another proxy which can handle them.

This option also supports reverse proxy configuration; a backend webserver can be embedded within a virtualhost URL space even if that server is hidden by another forward proxy.

An optional third argumentusername:password may be given, which defines the Basic authentication credentials to pass to the configured remote proxy. The credentials will always be sent without first waiting for the remote proxy to send a Basic authentication challenge. TheProxy-Chain-Auth environment variable has no effect if this argument is used.

ProxyRemoteMatchDirective

TheProxyRemoteMatch is identical to theProxyRemote directive, except that the first argument is aregular expression match against the requested URL.

ProxyRequestsDirective

This allows or prevents Apache httpd from functioning as a forward proxy server. (Setting ProxyRequests toOff does not disable use of theProxyPass directive.)

In a typical reverse proxy or gateway configuration, this option should be set toOff.

In order to get the functionality of proxying HTTP or FTP sites, you need alsomod_proxy_http ormod_proxy_ftp (or both) present in the server.

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

See also

• Forward and Reverse Proxies/Gateways

ProxySetDirective

This directive is used as an alternate method of setting any of the parameters available to Proxy balancers and workers normally done via theProxyPass directive. If used within a<Proxybalancer url|worker url> container directive, theurl argument is not required. As a side effect the respective balancer or worker gets created. This can be useful when doing reverse proxying via aRewriteRule instead of aProxyPass 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

ProxySourceAddressDirective

This directive allows to set a specific local address to bind to when connecting to a backend server.

ProxyStatusDirective

This directive determines whether or not proxy loadbalancer status data is displayed via themod_status server-status page.

ProxyTimeoutDirective

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.

ProxyViaDirective

This directive controls the use of theVia: HTTP header by the proxy. Its intended use is to control the flow of proxy requests along a chain of proxy servers. SeeRFC 2616 (HTTP/1.1), section 14.45 for an explanation ofVia: header lines.

• If set toOff, which is the default, no special processing is performed. If a request or reply contains aVia: header, it is passed through unchanged.
• If set toOn, each request and reply will get aVia: header line added for the current host.
• If set toFull, each generatedVia: header line will additionally have the Apache httpd server version shown as aVia: comment field.
• If set toBlock, every proxy request will have all itsVia: header lines removed. No newVia: header will be generated.