mod_proxy.xml revision a8d844bd3bf336e69cae4f063833aff8d044f6a1
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<modulesynopsis metafile="mod_proxy.xml.meta">
<name>mod_proxy</name>
<status>Extension</status>
<identifier>proxy_module</identifier>
<summary>
<note type="warning"><title>Warning</title>
<p>Do not enable proxying with <directive module="mod_proxy"
>ProxyRequests</directive> until you have <a href="#access"
>secured your server</a>. Open proxy servers are dangerous both to your
network and to the Internet at large.</p>
</note>
<p><module>mod_proxy</module> and related modules implement a
protocols as well as several different load balancing algorithms.
Third-party modules can add support for additional protocols and
load balancing algorithms.</p>
<p>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
<directive module="mod_so">LoadModule</directive> directive).
The set must include:</p>
<ul>
<li><module>mod_proxy</module>, which provides basic proxy
capabilities</li>
<li><module>mod_proxy_balancer</module> and one or more
balancer modules, if load balancing is required. (See
<module>mod_proxy_balancer</module> for more information.)</li>
<li>one or more proxy scheme, or protocol, modules:
<table border="1">
<tr><th>Protocol</th><th>Module</th></tr>
<tr><td>AJP13 (Apache JServe Protocol version
1.3)</td><td><module>mod_proxy_ajp</module></td></tr>
<tr><td>CONNECT (for
SSL)</td><td><module>mod_proxy_connect</module></td></tr>
<tr><td>FastCGI</td><td><module>mod_proxy_fcgi</module></td></tr>
<tr><td>ftp</td><td><module>mod_proxy_ftp</module></td></tr>
<tr><td>SCGI</td><td><module>mod_proxy_scgi</module></td></tr>
<tr><td>WS and WSS (Web-sockets)</td><td><module>mod_proxy_wstunnel</module></td></tr>
</table>
</li>
</ul>
<p>In addition, extended features are provided by other modules.
Caching is provided by <module>mod_cache</module> and related
protocol is provided by the <code>SSLProxy*</code> directives of
<module>mod_ssl</module>. These additional modules will need
to be loaded and configured to take advantage of these features.</p>
</summary>
<seealso><module>mod_cache</module></seealso>
<seealso><module>mod_proxy_ajp</module></seealso>
<seealso><module>mod_proxy_connect</module></seealso>
<seealso><module>mod_proxy_fcgi</module></seealso>
<seealso><module>mod_proxy_ftp</module></seealso>
<seealso><module>mod_proxy_http</module></seealso>
<seealso><module>mod_proxy_scgi</module></seealso>
<seealso><module>mod_proxy_wstunnel</module></seealso>
<seealso><module>mod_proxy_balancer</module></seealso>
<seealso><module>mod_ssl</module></seealso>
<section id="forwardreverse"><title>Forward Proxies and Reverse
<p>Apache HTTP Server can be configured in both a <dfn>forward</dfn> and
<dfn>reverse</dfn> proxy (also known as <dfn>gateway</dfn>) mode.</p>
<p>An ordinary <dfn>forward proxy</dfn> is an intermediate
server that sits between the client and the <em>origin
server</em>. 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.</p>
<p>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 <module>mod_cache</module>) to reduce network usage.</p>
<p>The forward proxy is activated using the <directive
module="mod_proxy">ProxyRequests</directive> directive. Because
forward proxies allow clients to access arbitrary sites through
your server and to hide their true origin, it is essential that
you <a href="#access">secure your server</a> so that only
authorized clients can access the proxy before activating a
forward proxy.</p>
<p>A <dfn>reverse proxy</dfn> (or <dfn>gateway</dfn>), 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.</p>
<p>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.</p>
<p>A reverse proxy is activated using the <directive
module="mod_proxy">ProxyPass</directive> directive or the
<code>[P]</code> flag to the <directive
module="mod_rewrite">RewriteRule</directive> directive. It is
<strong>not</strong> necessary to turn <directive
module="mod_proxy">ProxyRequests</directive> on in order to
configure a reverse proxy.</p>
</section> <!-- /forwardreverse -->
<section id="examples"><title>Basic Examples</title>
<p>The examples below are only a very basic idea to help you
get started. Please read the documentation on the individual
directives.</p>
<p>In addition, if you wish to have caching enabled, consult
the documentation from <module>mod_cache</module>.</p>
<example><title>Reverse Proxy</title>
<highlight language="config">
ProxyPass /foo http://foo.example.com/bar
ProxyPassReverse /foo http://foo.example.com/bar
</highlight>
</example>
<example><title>Forward Proxy</title>
<highlight language="config">
ProxyRequests On
ProxyVia On
<Proxy *>
Require host internal.example.com
</Proxy>
</highlight>
</example>
</section> <!-- /examples -->
<section id="workers"><title>Workers</title>
<p>The proxy manages the configuration of origin servers and their
communication parameters in objects called <dfn>workers</dfn>.
There are two built-in workers, the default forward proxy worker and the
default reverse proxy worker. Additional workers can be configured
explicitly.</p>
<p>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.</p>
<p>Explicitly configured workers are identified by their URL.
They are usually created and configured using
<directive module="mod_proxy">ProxyPass</directive> or
<directive module="mod_proxy">ProxyPassMatch</directive> when used
for a reverse proxy:</p>
<highlight language="config">
ProxyPass /example http://backend.example.com connectiontimeout=5 timeout=30
</highlight>
<p>This will create a worker associated with the origin server URL
values. When used in a forward proxy, workers are usually defined
via the <directive module="mod_proxy">ProxySet</directive> directive:</p>
<highlight language="config">
ProxySet http://backend.example.com connectiontimeout=5 timeout=30
</highlight>
<p>or alternatively using <directive module="mod_proxy">Proxy</directive>
and <directive module="mod_proxy">ProxySet</directive>:</p>
<highlight language="config">
<Proxy http://backend.example.com>
ProxySet connectiontimeout=5 timeout=30
</Proxy>
</highlight>
<p>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
<directive module="mod_proxy">ProxyPass</directive> 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.</p>
<p>The URL identifying a direct worker is the URL of its
origin server including any path components given:</p>
<highlight language="config">
ProxyPass /examples http://backend.example.com/examples
ProxyPass /docs http://backend.example.com/docs
</highlight>
<p>This example defines two different workers, each using a separate
connection pool and configuration.</p>
<note type="warning"><title>Worker Sharing</title>
<p>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</p>
<highlight language="config">
ProxyPass /apps http://backend.example.com/ timeout=60
ProxyPass /examples http://backend.example.com/examples timeout=10
</highlight>
<p>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 <code>/examples</code> will be <code>60</code> instead
of <code>10</code>!</p>
<p>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 <directive module="mod_proxy">ProxyPass</directive> directives.</p>
</note> <!-- /worker_sharing -->
<p>Explicitly configured workers come in two flavors:
<dfn>direct workers</dfn> and <dfn>(load) balancer workers</dfn>.
They support many important configuration attributes which are
described below in the <directive module="mod_proxy">ProxyPass</directive>
directive. The same attributes can also be set using
<directive module="mod_proxy">ProxySet</directive>.</p>
<p>The set of options available for a direct worker
depends on the protocol, which is specified in the origin server URL.
Available protocols include <code>ajp</code>, <code>fcgi</code>,
<code>ftp</code>, <code>http</code> and <code>scgi</code>.</p>
<p>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.</p>
<p>A balancer worker is created if its worker URL uses
<code>balancer</code> as the protocol scheme.
The balancer URL uniquely identifies the balancer worker.
Members are added to a balancer using
<directive module="mod_proxy">BalancerMember</directive>.</p>
</section> <!-- /workers -->
<section id="access"><title>Controlling access to your proxy</title>
<p>You can control who can access your proxy via the <directive
module="mod_proxy" type="section">Proxy</directive> control block as in
the following example:</p>
<highlight language="config">
<Proxy *>
Require ip 192.168.0
</Proxy>
</highlight>
<p>For more information on access control directives, see
<module>mod_authz_host</module>.</p>
<p>Strictly limiting access is essential if you are using a
forward proxy (using the <directive
module="mod_proxy">ProxyRequests</directive> 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 <directive
module="mod_proxy">ProxyPass</directive> directive with
<code>ProxyRequests Off</code>), access control is less
critical because clients can only contact the hosts that you
have specifically configured.</p>
>Proxy-Chain-Auth</a> environment variable.</p>
</section> <!-- /access -->
<section id="startup"><title>Slow Startup</title>
<p>If you're using the <directive module="mod_proxy"
>ProxyBlock</directive> 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.</p>
</section> <!-- /startup -->
<section id="intranet"><title>Intranet Proxy</title>
<p>An Apache httpd proxy server situated in an intranet needs to forward
external requests through the company's firewall (for this, configure
the <directive module="mod_proxy">ProxyRemote</directive> directive
to forward the respective <var>scheme</var> to the firewall proxy).
However, when it has to
access resources within the intranet, it can bypass the firewall when
accessing hosts. The <directive module="mod_proxy">NoProxy</directive>
directive is useful for specifying which hosts belong to the intranet and
should be accessed directly.</p>
<p>Users within an intranet tend to omit the local domain name from their
WWW requests, thus requesting "http://somehost/" instead of
let them get away with this and simply serve the request, implying a
configured local domain. When the <directive module="mod_proxy"
>ProxyDomain</directive> directive is used and the server is <a
href="#proxyrequests">configured for proxy service</a>, 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.</p>
</section> <!-- /intranet -->
<section id="envsettings"><title>Protocol Adjustments</title>
<p>For circumstances where <module>mod_proxy</module> is sending
requests to an origin server that doesn't properly implement
href="/env.html">environment variables</a> that can force the
<directive module="mod_env">SetEnv</directive> directive.</p>
<p>These are the <code>force-proxy-request-1.0</code> and
<code>proxy-nokeepalive</code> notes.</p>
<highlight language="config">
<Location /buggyappserver/>
ProxyPass http://buggyappserver:7001/foo/
SetEnv force-proxy-request-1.0 1
SetEnv proxy-nokeepalive 1
</Location>
</highlight>
</section> <!-- /envsettings -->
<section id="request-bodies"><title>Request Bodies</title>
<p>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
<code>Content-Length</code> request header. When passing these
requests on to the origin server, <module>mod_proxy_http</module>
will always attempt to send the <code>Content-Length</code>. 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 <a
href="/env.html">environment variables</a>. Setting
<code>proxy-sendcl</code> ensures maximum compatibility with
upstream servers by always sending the
<code>Content-Length</code>, while setting
<code>proxy-sendchunked</code> minimizes resource usage by using
chunked encoding.</p>
<p>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
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.</p>
<p><directive module="core">LimitRequestBody</directive> only applies to
request bodies that the server will spool to disk</p>
</section> <!-- /request-bodies -->
<section id="x-headers"><title>Reverse Proxy Request Headers</title>
<p>When acting in a reverse-proxy mode (using the <directive
module="mod_proxy">ProxyPass</directive> directive, for example),
<module>mod_proxy_http</module> adds several request headers in
order to pass information to the origin server. These headers
are:</p>
<dl>
<dt><code>X-Forwarded-For</code></dt>
<dd>The IP address of the client.</dd>
<dt><code>X-Forwarded-Host</code></dt>
<dd>The original host requested by the client in the <code>Host</code>
HTTP request header.</dd>
<dt><code>X-Forwarded-Server</code></dt>
<dd>The hostname of the proxy server.</dd>
</dl>
<p>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 <code>%{X-Forwarded-For}i</code> 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.</p>
<p>See also the <directive
module="mod_proxy">ProxyPreserveHost</directive> and <directive
module="mod_proxy">ProxyVia</directive> directives, which control
other request headers.</p>
</section> <!--/x-headers -->
<directivesynopsis type="section">
<name>Proxy</name>
<description>Container for directives applied to proxied resources</description>
<syntax><Proxy <var>wildcard-url</var>> ...</Proxy></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>Directives placed in <directive type="section">Proxy</directive>
sections apply only to matching proxied content. Shell-style wildcards are
allowed.</p>
<p>For example, the following will allow only hosts in
server:</p>
<highlight language="config">
<Proxy *>
Require host yournetwork.example.com
</Proxy>
</highlight>
<p>The following example will process all files in the <code>foo</code>
filter when they are sent through the proxy server:</p>
<highlight language="config">
<Proxy http://example.com/foo/*>
SetOutputFilter INCLUDES
</Proxy>
</highlight>
<note><title>Differences from the Location configuration section</title>
<p>A backend URL matches the configuration section if it begins with the
the <var>wildcard-url</var> 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/foobar. The matching of the final URL differs
from the behavior of the <directive type="section" module="core"
>Location</directive> section, which for purposes of this note
treats the final path component as if it ended in a slash.</p>
<p>For more control over the matching, see <directive type="section"
>ProxyMatch</directive>.</p>
</note>
</usage>
<seealso><directive type="section" module="mod_proxy">ProxyMatch</directive></seealso>
</directivesynopsis>
<directivesynopsis>
<name>ProxyBadHeader</name>
<description>Determines how to handle bad header lines in a
response</description>
<syntax>ProxyBadHeader IsError|Ignore|StartBody</syntax>
<default>ProxyBadHeader IsError</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyBadHeader</directive> directive determines the
behaviour of <module>mod_proxy</module> if it receives syntactically invalid
server. The following arguments are possible:</p>
<dl>
<dt><code>IsError</code></dt>
<dd>Abort the request and end up with a 502 (Bad Gateway) response. This is
the default behaviour.</dd>
<dt><code>Ignore</code></dt>
<dd>Treat bad header lines as if they weren't sent.</dd>
<dt><code>StartBody</code></dt>
<dd>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.</dd>
</dl>
</usage>
</directivesynopsis>
<directivesynopsis type="section">
<name>ProxyMatch</name>
<description>Container for directives applied to regular-expression-matched
proxied resources</description>
<syntax><ProxyMatch <var>regex</var>> ...</ProxyMatch></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive type="section">ProxyMatch</directive> directive is
identical to the <directive module="mod_proxy"
type="section">Proxy</directive> directive, except it matches URLs
using <glossary ref="regex">regular expressions</glossary>.</p>
<p>From 2.5.0 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
<module>mod_rewrite</module>. In order to prevent confusion, numbered
(unnamed) backreferences are ignored. Use named groups instead.</p>
<highlight language="config">
<ProxyMatch ^http://(?<sitename>[^/]+)>
require ldap-group cn=%{env:MATCH_SITENAME},ou=combined,o=Example
</ProxyMatch>
</highlight>
</usage>
<seealso><directive type="section" module="mod_proxy">Proxy</directive></seealso>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPreserveHost</name>
<description>Use incoming Host HTTP request header for proxy
request</description>
<syntax>ProxyPreserveHost On|Off</syntax>
<default>ProxyPreserveHost Off</default>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<compatibility>Usable in directory
context in 2.3.3 and later.</compatibility>
<usage>
<p>When enabled, this option will pass the Host: line from the incoming
request to the proxied host, instead of the hostname specified in the
<directive>ProxyPass</directive> line.</p>
<p>This option should normally be turned <code>Off</code>. 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.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyRequests</name>
<description>Enables forward (standard) proxy requests</description>
<syntax>ProxyRequests On|Off</syntax>
<default>ProxyRequests Off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This allows or prevents Apache httpd from functioning as a forward proxy
server. (Setting ProxyRequests to <code>Off</code> does not disable use of
the <directive module="mod_proxy">ProxyPass</directive> directive.)</p>
<p>In a typical reverse proxy or gateway configuration, this
option should be set to
<code>Off</code>.</p>
<p>In order to get the functionality of proxying HTTP or FTP sites, you
need also <module>mod_proxy_http</module> or <module>mod_proxy_ftp</module>
(or both) present in the server.</p>
<p>In order to get the functionality of (forward) proxying HTTPS sites, you
need <module>mod_proxy_connect</module> enabled in the server.</p>
<note type="warning"><title>Warning</title>
<p>Do not enable proxying with <directive
module="mod_proxy">ProxyRequests</directive> until you have <a
href="#access">secured your server</a>. Open proxy servers are dangerous
both to your network and to the Internet at large.</p>
</note>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyRemote</name>
<description>Remote proxy used to handle certain requests</description>
<syntax>ProxyRemote <var>match</var> <var>remote-server</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This defines remote proxies to this proxy. <var>match</var> 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 <code>*</code> to indicate
the server should be contacted for all requests. <var>remote-server</var> is
a partial URL for the remote server. Syntax:</p>
<example>
<dfn>remote-server</dfn> =
<var>scheme</var>://<var>hostname</var>[:<var>port</var>]
</example>
<p><var>scheme</var> is effectively the protocol that should be used to
communicate with the remote server; only <code>http</code> and <code>https</code>
are supported by this module. When using <code>https</code>, the requests
are forwarded through the remote proxy using the HTTP CONNECT method.</p>
<example><title>Example</title>
<highlight language="config">
ProxyRemote * http://cleverproxy.localdomain
ProxyRemote ftp http://ftpproxy.mydomain:8080
</highlight>
</example>
<p>In the last example, the proxy will forward FTP requests, encapsulated
as yet another HTTP proxy request, to another proxy which can handle
them.</p>
<p>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.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyRemoteMatch</name>
<description>Remote proxy used to handle requests matched by regular
expressions</description>
<syntax>ProxyRemoteMatch <var>regex</var> <var>remote-server</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyRemoteMatch</directive> is identical to the
<directive module="mod_proxy">ProxyRemote</directive> directive, except the
first argument is a <glossary ref="regex">regular expression</glossary>
match against the requested URL.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>BalancerGrowth</name>
<description>Number of additional Balancers that can be added Post-configuration</description>
<syntax>BalancerGrowth <var>#</var></syntax>
<default>BalancerGrowth 5</default>
<contextlist><context>server config</context><context>virtual host</context></contextlist>
<compatibility>BalancerGrowth is only available in Apache HTTP Server 2.3.13
and later.</compatibility>
<usage>
<p>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 1 pre-configured Balancer.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>BalancerPersist</name>
<description>Attempt to persist changes made by the Balancer Manager across restarts.</description>
<syntax>BalancerPersist On|Off</syntax>
<default>BalancerPersist Off</default>
<contextlist><context>server config</context><context>virtual host</context></contextlist>
<compatibility>BalancerPersist is only available in Apache HTTP Server 2.5.0
and later.</compatibility>
<usage>
<p>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
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPassInherit</name>
<description>Inherit ProxyPass directives defined from the main server</description>
<syntax>ProxyPassInherit On|Off</syntax>
<default>ProxyPassInherit On</default>
<contextlist><context>server config</context><context>virtual host</context></contextlist>
<compatibility>ProxyPassInherit is only available in Apache HTTP Server 2.5.0 and later.
and later.</compatibility>
<usage>
<directive module="mod_proxy">ProxyPass</directive>
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.</p>
<p>The setting in the global server defines the default for all vhosts.</p>
<p>Disabling ProxyPassInherit also disables <directive module="mod_proxy">BalancerInherit</directive>.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>BalancerInherit</name>
<syntax>BalancerInherit On|Off</syntax>
<default>BalancerInherit On</default>
<contextlist><context>server config</context><context>virtual host</context></contextlist>
<compatibility>BalancerInherit is only available in Apache HTTP Server 2.4.4 and later.
and later.</compatibility>
<usage>
Balancers and Workers 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.</p>
<p>The setting in the global server defines the default for all vhosts.</p>
<p>Disabling <directive module="mod_proxy">ProxyPassInherit</directive> also disables BalancerInherit.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>BalancerMember</name>
<description>Add a member to a load balancing group</description>
<syntax>BalancerMember [<var>balancerurl</var>] <var>url</var> [<var
>key=value [key=value ...]]</var></syntax>
<contextlist><context>directory</context>
</contextlist>
<usage>
<p>This directive adds a member to a load balancing group. It could be used
within a <code><Proxy <var>balancer://</var>...></code> container
directive, and can take any of the key value pair parameters available to
<directive module="mod_proxy">ProxyPass</directive> directives.</p>
<p>One additional parameter is available only to <directive
module="mod_proxy">BalancerMember</directive> directives:
<var>loadfactor</var>. This is the member load factor - a number between 1
(default) and 100, which defines the weighted load to be applied to the
member in question.</p>
<p>The balancerurl is only needed when not in <code><Proxy <var>balancer://</var>...></code>
container directive. It corresponds to the url of a balancer defined in
<directive module="mod_proxy">ProxyPass</directive> directive.</p>
<p>The path component of the balancer URL in any
<code><Proxy <var>balancer://</var>...></code> container directive
is ignored.</p>
<p>Trailing slashes should typically be removed from the URL of a
<code>BalancerMember</code>.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxySet</name>
<description>Set various Proxy balancer or member parameters</description>
<syntax>ProxySet <var>url</var> <var>key=value [key=value ...]</var></syntax>
<contextlist><context>directory</context>
</contextlist>
<usage>
<p>This directive is used as an alternate method of setting any of the
parameters available to Proxy balancers and workers normally done via the
<directive module="mod_proxy">ProxyPass</directive> directive. If used
within a <code><Proxy <var>balancer url|worker url</var>></code>
container directive, the <var>url</var> 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
<directive module="mod_rewrite">RewriteRule</directive> instead of a
<directive module="mod_proxy">ProxyPass</directive> directive.</p>
<example>
<highlight language="config">
<Proxy balancer://hotcluster>
BalancerMember http://www2.example.com:8080 loadfactor=1
BalancerMember http://www3.example.com:8080 loadfactor=2
ProxySet lbmethod=bytraffic
</Proxy>
</highlight>
</example>
<highlight language="config">
<Proxy http://backend>
ProxySet keepalive=On
</Proxy>
</highlight>
<highlight language="config">
ProxySet balancer://foo lbmethod=bytraffic timeout=15
</highlight>
<highlight language="config">
ProxySet ajp://backend:7001 timeout=15
</highlight>
<note type="warning"><title>Warning</title>
<p>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.</p>
</note>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPass</name>
<description>Maps remote servers into the local server URL-space</description>
<syntax>ProxyPass [<var>path</var>] !|<var>url</var> [<var>key=value</var>
<var>[key=value</var> ...]] [nocanon] [interpolate] [noquery]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>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 <dfn>reverse
proxy</dfn> or <dfn>gateway</dfn>. The <var>path</var> is the name of
a local virtual path; <var>url</var> is a partial URL for the
remote server and cannot include a query string.</p>
<note><strong>Note: </strong>This directive cannot be used within a
<code><Directory></code> context.</note>
<note type="warning">The <directive
module="mod_proxy">ProxyRequests</directive> directive should
usually be set <strong>off</strong> when using
<directive>ProxyPass</directive>.</note>
<p>Support for using a Unix Domain Socket is available by using a url target
the socket is local, the hostname used (in this case <code>localhost</code>)
is moot.</p>
<note><strong>Note:</strong> The path associated with the <code>unix:</code>
URL is <directive>DefaultRuntimeDir</directive> aware.</note>
<note><strong>Note:</strong> <directive>RewriteRule</directive> requires
the <code>[P,NE]</code> option to prevent the <code>'|'</code> character
from being escaped.</note>
then</p>
<highlight language="config">
ProxyPass http://backend.example.com/
</Location>
</highlight>
<p>will cause a local request for
<p>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 the
<highlight language="config">
</highlight>
<note type="warning">
<p>If the first argument ends with a trailing <strong>/</strong>, the second
argument should also end with a trailing <strong>/</strong> and vice
versa. Otherwise the resulting requests to the backend may miss some
needed slashes and do not deliver the expected results.
</p>
</note>
<p>The <code>!</code> directive is useful in situations where you don't want
<highlight language="config">
ProxyPass http://backend.example.com/
</Location>
ProxyPass !
</Location>
</highlight>
<highlight language="config">
</highlight>
<note type="warning"><title>Ordering ProxyPass Directives</title>
<p>The configured <directive module="mod_proxy">ProxyPass</directive>
and <directive module="mod_proxy">ProxyPassMatch</directive>
rules are checked in the order of configuration. The first rule that
matches wins. So usually you should sort conflicting
<directive module="mod_proxy">ProxyPass</directive> rules starting with the
longest URLs first. Otherwise later rules for longer URLS will be hidden
by any earlier rule which uses a leading substring of the URL. Note that
there is some relation with worker sharing. In contrast, only one
<directive module="mod_proxy">ProxyPass</directive> directive can be placed
in a <directive module="core">Location</directive> block, and the most
specific location will take precedence.</p>
<p>For the same reasons exclusions must come <em>before</em> the
general <directive>ProxyPass</directive> directives.</p>
</note> <!-- /ordering_proxypass -->
<p>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 <directive>ProxyPass</directive> directive
using <code>key=value</code> parameters, described in the table
below.</p>
<p>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 <code>max</code> parameter to reduce the number from
the default. Use the <code>ttl</code> parameter to set an optional
time to live; connections which have been unused for at least
<code>ttl</code> seconds will be closed. <code>ttl</code> can be used
to avoid using a connection which is subject to closing because of the
backend server's keep-alive timeout.</p>
<p>The pool of connections is maintained per web server child
process, and <code>max</code> and other settings are not coordinated
among all child processes, except when only one child process is allowed
by configuration or MPM design.</p>
<example><title>Example</title>
<highlight language="config">
ProxyPass /example http://backend.example.com max=20 ttl=120 retry=300
</highlight>
</example>
<table border="2"><tr><th>BalancerMember parameters</th></tr></table>
<table>
<tr><th>Parameter</th>
<th>Default</th>
<th>Description</th></tr>
<tr><td>min</td>
<td>0</td>
<td>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.</td></tr>
<tr><td>max</td>
<td>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
<directive>ThreadsPerChild</directive> directive.</td></tr>
<tr><td>smax</td>
<td>max</td>
<td>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 <code>ttl</code> 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.</td></tr>
<tr><td>acquire</td>
<td>-</td>
<td>If set this will be the maximum time to wait for a free
connection in the connection pool, in milliseconds. If there are no free
connections in the pool the Apache httpd will return <code>SERVER_BUSY</code>
status to the client.
</td></tr>
<tr><td>connectiontimeout</td>
<td>timeout</td>
<td>Connect timeout in seconds.
The number of seconds Apache httpd waits for the creation of a connection to
the backend to complete. By adding a postfix of ms the timeout can be
also set in milliseconds.
</td></tr>
<tr><td>disablereuse</td>
<td>Off</td>
<td>This parameter should be used when you want to force mod_proxy
to immediately close a connection to the backend after being used, and
thus, disable its persistent connection and pool for that backend.
This helps in various situations where a firewall between Apache
httpd and
the backend server (regardless of protocol) tends to silently
drop connections or when backends themselves may be under round-
robin DNS. To disable connection pooling reuse,
set this property value to <code>On</code>.
</td></tr>
<tr><td>flushpackets</td>
<td>off</td>
<td>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
no input has been received for 'flushwait' milliseconds.
Currently this is in effect only for AJP.
</td></tr>
<tr><td>flushwait</td>
<td>10</td>
<td>The time to wait for additional input, in milliseconds, before
flushing the output brigade if 'flushpackets' is 'auto'.
</td></tr>
<tr><td>iobuffersize</td>
<td>8192</td>
<td>Adjusts the size of the internal scratchpad IO buffer. This allows you
to override the <directive>ProxyIOBufferSize</directive> for a specific worker.
This must be at least 512 or set to 0 for the system default of 8192.
</td></tr>
<tr><td>keepalive</td>
<td>Off</td>
<td><p>This parameter should be used when you have a firewall between your
Apache httpd and the backend server, who tend to drop inactive connections.
This flag will tell the Operating System to send <code>KEEP_ALIVE</code>
messages on inactive connections and thus prevent the firewall to drop the connection.
To enable keepalive set this property value to <code>On</code>. </p>
<p>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.</p>
</td></tr>
<tr><td>lbset</td>
<td>0</td>
<td>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.
</td></tr>
<tr><td>ping</td>
<td>0</td>
<td>Ping property tells the webserver to "test" the connection to
the backend before forwarding the request. For negative values
the test is a simple socket check, for positive values it's
a more functional check, dependent upon the protocol. For AJP, it causes
<module>mod_proxy_ajp</module>to send a <code>CPING</code>
request on the ajp13 connection (implemented on Tomcat 3.3.2+, 4.1.28+
and 5.0.13+). For HTTP, it causes <module>mod_proxy_http</module>
to send a <code>100-Continue</code> to the backend (only valid for
effect). In both cases the parameter is the delay in seconds to wait
for the reply.
This feature has been added to avoid problems with hung and
busy backends.
This will increase the network traffic during the normal operation
which could be an issue, but it will lower the
traffic in case some of the cluster nodes are down or busy.
By adding a postfix of ms the delay can be also set in
milliseconds.
</td></tr>
<tr><td>receivebuffersize</td>
<td>0</td>
proxied connections. This allows you to override the
<directive>ProxyReceiveBufferSize</directive> for a specific worker.
This must be at least 512 or set to 0 for the system default.
</td></tr>
<tr><td>redirect</td>
<td>-</td>
<td>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.
</td></tr>
<tr><td>retry</td>
<td>60</td>
<td>Connection pool worker retry timeout in seconds.
If the connection pool worker to the backend server is in the error state,
Apache httpd will not forward any requests to that server until the timeout
expires. This enables to shut down the backend server for maintenance,
and bring it back online later. A value of 0 means always retry workers
in an error state with no timeout.
</td></tr>
<tr><td>route</td>
<td>-</td>
<td>Route of the worker when used inside load balancer.
The route is a value appended to session id.
</td></tr>
<tr><td>status</td>
<td>-</td>
<td>Single letter value defining the initial status of
this worker.
<table>
<tr><td>D: Worker is disabled and will not accept any requests.</td></tr>
<tr><td>S: Worker is administratively stopped.</td></tr>
<tr><td>I: Worker is in ignore-errors mode, and will always be considered available.</td></tr>
<tr><td>H: Worker is in hot-standby mode and will only be used if no other
viable workers are available.</td></tr>
<tr><td>E: Worker is in an error state.</td></tr>
<tr><td>N: Worker is in drain mode, and will only accept existing sticky sessions
destined for itself and ignore all other requests.</td></tr>
</table>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.
</td></tr>
<tr><td>timeout</td>
<td><directive module="mod_proxy">ProxyTimeout</directive></td>
<td>Connection timeout in seconds.
The number of seconds Apache httpd waits for data sent by / to the backend.
</td></tr>
<tr><td>ttl</td>
<td>-</td>
<td>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.
</td></tr>
</table>
<p>If the Proxy directive scheme starts with the
<code>balancer://</code> (eg: <code>balancer://cluster</code>,
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 <module>mod_proxy_balancer</module>
for more information about how the balancer works.
</p>
<table border="2"><tr><th>Balancer parameters</th></tr></table>
<table>
<tr><th>Parameter</th>
<th>Default</th>
<th>Description</th></tr>
<tr><td>lbmethod</td>
<td>byrequests</td>
<td>Balancer load-balance method. Select the load-balancing scheduler
method to use. Either <code>byrequests</code>, to perform weighted
request counting, <code>bytraffic</code>, to perform weighted
traffic byte count balancing, or <code>bybusyness</code>, to perform
pending request balancing. Default is <code>byrequests</code>.
</td></tr>
<tr><td>maxattempts</td>
<td>One less than the number of workers, or 1 with a single worker.</td>
<td>Maximum number of failover attempts before giving up.
</td></tr>
<tr><td>nofailover</td>
<td>Off</td>
<td>If set to <code>On</code> 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.
</td></tr>
<tr><td>stickysession</td>
<td>-</td>
<td>Balancer sticky session name. The value is usually set to something
like <code>JSESSIONID</code> or <code>PHPSESSIONID</code>,
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.
</td></tr>
<tr><td>stickysessionsep</td>
<td>"."</td>
<td>Sets the separation symbol in the session cookie. Some backend application servers
do not use the '.' as the symbol. For example the Oracle Weblogic server uses
'!'. The correct symbol can be set using this option. The setting of 'Off'
signifies that no symbol is used.
</td></tr>
<tr><td>scolonpathdelim</td>
<td>Off</td>
<td>If set to <code>On</code> the semi-colon character ';' will be
is mainly used to emulate mod_jk's behavior when dealing with paths such
as <code>JSESSIONID=6736bcf34;foo=aabfa</code>
</td></tr>
<tr><td>timeout</td>
<td>0</td>
<td>Balancer timeout in seconds. If set this will be the maximum time
to wait for a free worker. Default is not to wait.
</td></tr>
<tr><td>failonstatus</td>
<td>-</td>
<td>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.
</td></tr>
<tr><td>failontimeout</td>
<td>Off</td>
<td>If set, an IO read timeout after a request is sent to the backend will
force the worker into error state. Worker recovery behaves the same as other
worker errors.
</td></tr>
<tr><td>nonce</td>
<td><auto></td>
<td>The protective nonce used in the <code>balancer-manager</code> application page.
The default is to use an automatically determined UUID-based
nonce, to provide for further protection for the page. If set,
then the nonce is set to that value. A setting of <code>None</code>
disables all nonce checking.
<note><title>Note</title>
<p>In addition to the nonce, the <code>balancer-manager</code> page
should be protected via an ACL.</p>
</note>
</td></tr>
<tr><td>growth</td>
<td>0</td>
<td>Number of additional BalancerMembers to allow to be added
to this balancer in addition to those defined at configuration.
</td></tr>
<tr><td>forcerecovery</td>
<td>On</td>
<td>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 <code>Off</code>.
</td></tr>
</table>
<p>A sample balancer setup</p>
<highlight language="config">
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>
</highlight>
<p>Setting up a hot-standby, that will only be used if no other
members are available</p>
<highlight language="config">
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 server below is on hot standby
BalancerMember ajp://1.2.3.6:8009 status=+H
ProxySet lbmethod=bytraffic
</Proxy>
</highlight>
<p>Normally, mod_proxy will canonicalise ProxyPassed URLs.
But this may be incompatible with some backends, particularly those
that make use of <var>PATH_INFO</var>. The optional <var>nocanon</var>
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.</p>
<p>Normally, mod_proxy will include the query string when
generating the <var>SCRIPT_FILENAME</var> environment variable.
The optional <var>noquery</var> keyword (available in
httpd 2.4.1 and later) prevents this.</p>
<p>When used inside a <directive type="section" module="core"
>Location</directive> section, the first argument is omitted and the local
directory is obtained from the <directive type="section" module="core"
>Location</directive>. The same will occur inside a
<directive type="section" module="core">LocationMatch</directive> section,
however ProxyPass does not interpret the regexp as such, so it is necessary
to use <directive>ProxyPassMatch</directive> in this situation instead.</p>
<p>This directive is not supported in <directive type="section" module="core"
>Directory</directive> or <directive type="section" module="core"
>Files</directive> sections.</p>
<p>If you require a more flexible reverse-proxy configuration, see the
<directive module="mod_rewrite">RewriteRule</directive> directive with the
<code>[P]</code> flag.</p>
<p>The optional <var>interpolate</var> keyword (available in
httpd 2.2.9 and later), in combination with
<directive>ProxyPassInterpolateEnv</directive> causes the ProxyPass
to interpolate environment variables, using the syntax
<var>${VARNAME}</var>. Note that many of the standard CGI-derived
environment variables will not exist when this interpolation happens,
so you may still have to resort to <module>mod_rewrite</module>
for complex rules. Also note that interpolation is not supported
within the scheme portion of a URL. Dynamic determination of the
scheme can be accomplished with <module>mod_rewrite</module> as in the
following example.</p>
<highlight language="config">
RewriteEngine On
RewriteCond %{HTTPS} =off
RewriteRule . - [E=protocol:http]
RewriteCond %{HTTPS} =on
RewriteRule . - [E=protocol:https]
</highlight>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPassMatch</name>
<description>Maps remote servers into the local server URL-space using regular expressions</description>
<syntax>ProxyPassMatch [<var>regex</var>] !|<var>url</var> [<var>key=value</var>
<var>[key=value</var> ...]]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>This directive is equivalent to <directive module="mod_proxy">ProxyPass</directive>,
but makes use of regular expressions, instead of simple prefix matching. The
supplied regular expression is matched against the <var>url</var>, and if it
matches, the server will substitute any parenthesized matches into the given
string and use it as a new <var>url</var>.</p>
<note><strong>Note: </strong>This directive cannot be used within a
<code><Directory></code> context.</note>
then</p>
<highlight language="config">
ProxyPassMatch ^(/.*\.gif)$ http://backend.example.com$1
</highlight>
<p>will cause a local request for
<note><title>Note</title>
<p>The URL argument must be parsable as a URL <em>before</em> regexp
substitutions (as well as after). This limits the matches you can use.
For instance, if we had used</p>
<highlight language="config">
ProxyPassMatch ^(/.*\.gif)$ http://backend.example.com:8000$1
</highlight>
<p>in our previous example, it would fail with a syntax error
at server startup. This is a bug (PR 46665 in the ASF bugzilla),
and the workaround is to reformulate the match:</p>
<highlight language="config">
ProxyPassMatch ^/(.*\.gif)$ http://backend.example.com:8000/$1
</highlight>
</note>
<p>The <code>!</code> directive is useful in situations where you don't want
to reverse-proxy a subdirectory.</p>
<p>When used inside a <directive type="section" module="core"
>LocationMatch</directive> section, the first argument is omitted and the
regexp is obtained from the <directive type="section" module="core"
>LocationMatch</directive>.</p>
<p>If you require a more flexible reverse-proxy configuration, see the
<directive module="mod_rewrite">RewriteRule</directive> directive with the
<code>[P]</code> flag.</p>
<note type="warning">
<title>Security Warning</title>
<p>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.</p>
</note>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPassReverse</name>
<description>Adjusts the URL in HTTP response headers sent from a reverse
proxied server</description>
<syntax>ProxyPassReverse [<var>path</var>] <var>url</var>
[<var>interpolate</var>]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>This directive lets Apache httpd adjust the URL in the <code>Location</code>,
<code>Content-Location</code> and <code>URI</code> headers on HTTP
redirect responses. This is essential when Apache httpd is used as a
reverse proxy (or gateway) to avoid by-passing the reverse proxy
because of HTTP redirects on the backend servers which stay behind
the reverse proxy.</p>
<p>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 by-pass the proxy. To rewrite HTML content to
match the proxy, you must load and enable <module>mod_proxy_html</module>.
</p>
<p><var>path</var> is the name of a local virtual path. <var>url</var> is a
partial URL for the remote server - the same way they are used for the
<directive module="mod_proxy">ProxyPass</directive> directive.</p>
<p>For example, suppose the local server has address
<highlight language="config">
ProxyPassReverseCookieDomain backend.example.com public.example.com
</highlight>
<p>will not only cause a local request for the
(the functionality <code>ProxyPass</code> provides here). It also takes care
redirect response to the client. Note that the hostname used for
constructing the URL is chosen in respect to the setting of the <directive
module="core">UseCanonicalName</directive> directive.</p>
<p>Note that this <directive>ProxyPassReverse</directive> directive can
also be used in conjunction with the proxy pass-through feature
(<code>RewriteRule ... [P]</code>) from <module>mod_rewrite</module>
because it doesn't depend on a corresponding <directive module="mod_proxy"
>ProxyPass</directive> directive.</p>
<p>The optional <var>interpolate</var> keyword (available in
httpd 2.2.9 and later), used together with
<directive>ProxyPassInterpolateEnv</directive>, enables interpolation
of environment variables specified using the format <var>${VARNAME}</var>.
Note that interpolation is not supported within the scheme portion of a
URL.</p>
<p>When used inside a <directive type="section" module="core"
>Location</directive> section, the first argument is omitted and the local
directory is obtained from the <directive type="section" module="core"
>Location</directive>. The same occurs inside a <directive type="section"
module="core">LocationMatch</directive> 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 <directive type="section" module="core"
>Location</directive> section.</p>
<p>This directive is not supported in <directive type="section" module="core"
>Directory</directive> or <directive type="section" module="core"
>Files</directive> sections.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPassReverseCookieDomain</name>
<description>Adjusts the Domain string in Set-Cookie headers from a reverse-
proxied server</description>
<syntax>ProxyPassReverseCookieDomain <var>internal-domain</var>
<var>public-domain</var> [<var>interpolate</var>]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>Usage is basically similar to
<directive module="mod_proxy">ProxyPassReverse</directive>, but instead of
rewriting headers that are a URL, this rewrites the <code>domain</code>
string in <code>Set-Cookie</code> headers.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPassReverseCookiePath</name>
<description>Adjusts the Path string in Set-Cookie headers from a reverse-
proxied server</description>
<syntax>ProxyPassReverseCookiePath <var>internal-path</var>
<var>public-path</var> [<var>interpolate</var>]</syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>
Useful in conjunction with
<directive module="mod_proxy">ProxyPassReverse</directive>
in situations where backend URL paths are mapped to public paths on the
reverse proxy. This directive rewrites the <code>path</code> string in
<code>Set-Cookie</code> headers. If the beginning of the cookie path matches
<var>internal-path</var>, the cookie path will be replaced with
<var>public-path</var>.
</p><p>
In the example given with
<directive module="mod_proxy">ProxyPassReverse</directive>, the directive:
</p>
<highlight language="config">
</highlight>
<p>
will rewrite a cookie with backend path <code>/</code> (or
</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyBlock</name>
<description>Disallow proxy requests to certain hosts</description>
<syntax>ProxyBlock *|<var>hostname</var>|<var>partial-hostname</var> [<var>hostname</var>|<var>partial-hostname</var>]...</syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyBlock</directive> directive can be used to
block FTP or HTTP access to certain hosts via the proxy, based on
a full or partial hostname match, or, if applicable, an IP address
comparison.</p>
<p>Each of the arguments to the <directive>ProxyBlock</directive>
directive can be either <code>*</code> or a alphanumeric string.
At startup, the module will attempt to resolve every alphanumeric
string from a DNS name to a set of IP addresses, but any DNS errors
are ignored.</p>
<p>If an asterisk "<code>*</code>" argument is specified,
<module>mod_proxy</module> will deny access to all FTP or HTTP
sites.</p>
<p>Otherwise, for any request for an HTTP or FTP resource via the
proxy, <module>mod_proxy</module> will check the hostname of the
request URI against each specified string. If a partial string
match is found, access is denied. If no matches against hostnames
are found, and a remote (forward) proxy is configured using
<directive>ProxyRemote</directive> or
<directive>ProxyRemoteMatch</directive>, access is allowed. If no
remote (forward) proxy is configured, the IP address of the
hostname from the URI is compared against all resolved IP
addresses determined at startup. Access is denied if any match is
found.</p>
<p>Note that the DNS lookups may slow down the startup time of the
server.</p>
<example><title>Example</title>
<highlight language="config">
</highlight>
</example>
<p>Note that <code>example</code> would also be sufficient to match any
of these sites.</p>
<p>Hosts would also be matched if referenced by IP address.</p>
<p>Note also that</p>
<highlight language="config">
ProxyBlock *
</highlight>
<p>blocks connections to all sites.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyReceiveBufferSize</name>
<description>Network buffer size for proxied HTTP and FTP
connections</description>
<syntax>ProxyReceiveBufferSize <var>bytes</var></syntax>
<default>ProxyReceiveBufferSize 0</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyReceiveBufferSize</directive> directive specifies an
for increased throughput. It has to be greater than <code>512</code> or set
to <code>0</code> to indicate that the system's default buffer size should
be used.</p>
<example><title>Example</title>
<highlight language="config">
ProxyReceiveBufferSize 2048
</highlight>
</example>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyIOBufferSize</name>
<description>Determine size of internal data throughput buffer</description>
<syntax>ProxyIOBufferSize <var>bytes</var></syntax>
<default>ProxyIOBufferSize 8192</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyIOBufferSize</directive> 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 <code>512</code>.</p>
<p>In almost every case there's no reason to change that value.</p>
<p>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 <code>packetSize</code> attribute of
your AJP connector on the Tomcat side! The attribute
<code>packetSize</code> is only available in Tomcat <code>5.5.20+</code>
and <code>6.0.2+</code></p>
<p>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.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyMaxForwards</name>
<description>Maximium number of proxies that a request can be forwarded
through</description>
<syntax>ProxyMaxForwards <var>number</var></syntax>
<default>ProxyMaxForwards -1</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyMaxForwards</directive> directive specifies the
maximum number of proxies through which a request may pass, if there's no
<code>Max-Forwards</code> header supplied with the request. This may
be set to prevent infinite proxy loops, or a DoS attack.</p>
<example><title>Example</title>
<highlight language="config">
ProxyMaxForwards 15
</highlight>
</example>
<p>Note that setting <directive>ProxyMaxForwards</directive> is a
setting <code>Max-Forwards</code> if the Client didn't set it.
Earlier Apache httpd versions would always set it. A negative
<directive>ProxyMaxForwards</directive> value, including the
default -1, gives you protocol-compliant behaviour, but may
leave you open to loops.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>NoProxy</name>
<description>Hosts, domains, or networks that will be connected to
directly</description>
<syntax>NoProxy <var>host</var> [<var>host</var>] ...</syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This directive is only useful for Apache httpd proxy servers within
intranets. The <directive>NoProxy</directive> directive specifies a
spaces. A request to a host which matches one or more of these is
always served directly, without forwarding to the configured
<directive module="mod_proxy">ProxyRemote</directive> proxy server(s).</p>
<example><title>Example</title>
<highlight language="config">
ProxyRemote * http://firewall.example.com:81
</highlight>
</example>
<p>The <var>host</var> arguments to the <directive>NoProxy</directive>
directive are one of the following type list:</p>
<dl>
<!-- ===================== Domain ======================= -->
<dt><var><a name="domain" id="domain">Domain</a></var></dt>
<dd>
<p>A <dfn>Domain</dfn> is a partially qualified DNS domain name, preceded
by a period. It represents a list of hosts which logically belong to the
all ending in <var>Domain</var>).</p>
<example><title>Examples</title>
.com .example.org.
</example>
<p>To distinguish <var>Domain</var>s from <var><a href="#hostname"
>Hostname</a></var>s (both syntactically and semantically; a DNS domain can
have a DNS A record, too!), <var>Domain</var>s are always written with a
leading period.</p>
<note><title>Note</title>
<p>Domain name comparisons are done without regard to the case, and
<var>Domain</var>s are always assumed to be anchored in the root of the
equal. Since a domain comparison does not involve a DNS lookup, it is much
more efficient than subnet comparison.</p>
</note></dd>
<!-- ===================== SubNet ======================= -->
<dt><var><a name="subnet" id="subnet">SubNet</a></var></dt>
<dd>
<p>A <dfn>SubNet</dfn> 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 <var>SubNet</var>. 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:</p>
<dl>
<dt><code>192.168</code> or <code>192.168.0.0</code></dt>
<dd>the subnet 192.168.0.0 with an implied netmask of 16 valid bits
(sometimes used in the netmask form <code>255.255.0.0</code>)</dd>
valid bits (also used in the form <code>255.255.248.0</code>)</dd>
</dl>
<p>As a degenerate case, a <em>SubNet</em> with 32 valid bits is the
equivalent to an <var><a href="#ipaddr">IPAddr</a></var>, while a <var>SubNet</var> with zero
<var>_Default_</var>, matching any IP address.</p></dd>
<!-- ===================== IPAddr ======================= -->
<dt><var><a name="ipaddr" id="ipaddr">IPAddr</a></var></dt>
<dd>
<p>A <dfn>IPAddr</dfn> 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.</p>
<example><title>Example</title>
192.168.123.7
</example>
<note><title>Note</title>
<p>An <var>IPAddr</var> does not need to be resolved by the DNS system, so
it can result in more effective apache performance.</p>
</note></dd>
<!-- ===================== Hostname ======================= -->
<dt><var><a name="hostname" id="hostname">Hostname</a></var></dt>
<dd>
<p>A <dfn>Hostname</dfn> is a fully qualified DNS domain name which can
be resolved to one or more <var><a href="#ipaddr">IPAddrs</a></var> via the
DNS domain name service. It represents a logical host (in contrast to
<var><a href="#domain">Domain</a></var>s, see above) and must be resolvable
to at least one <var><a href="#ipaddr">IPAddr</a></var> (or often to a list
of hosts with different <var><a href="#ipaddr">IPAddr</a></var>s).</p>
<example><title>Examples</title>
prep.ai.example.edu<br />
</example>
<note><title>Note</title>
<p>In many situations, it is more effective to specify an <var><a
href="#ipaddr">IPAddr</a></var> in place of a <var>Hostname</var> 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.</p>
<p><var>Hostname</var> comparisons are done without regard to the case,
and <var>Hostname</var>s are always assumed to be anchored in the root
considered equal.</p>
</note></dd>
</dl>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyTimeout</name>
<description>Network timeout for proxied requests</description>
<syntax>ProxyTimeout <var>seconds</var></syntax>
<default>Value of <directive module="core">Timeout</directive></default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This directive allows a user to specifiy a timeout on proxy requests.
would rather just return a timeout and fail gracefully instead of waiting
however long it takes the server to return.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyDomain</name>
<description>Default domain name for proxied requests</description>
<syntax>ProxyDomain <var>Domain</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This directive is only useful for Apache httpd proxy servers within
intranets. The <directive>ProxyDomain</directive> 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 <var>Domain</var> appended
will be generated.</p>
<example><title>Example</title>
<highlight language="config">
ProxyRemote * http://firewall.example.com:81<br />
ProxyDomain .example.com
</highlight>
</example>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyVia</name>
<description>Information provided in the <code>Via</code> HTTP response
header for proxied requests</description>
<syntax>ProxyVia On|Off|Full|Block</syntax>
<default>ProxyVia Off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This directive controls the use of the <code>Via:</code> HTTP
header by the proxy. Its intended use is to control the flow of
proxy requests along a chain of proxy servers. See <a
14.45 for an explanation of <code>Via:</code> header lines.</p>
<ul>
<li>If set to <code>Off</code>, which is the default, no special processing
is performed. If a request or reply contains a <code>Via:</code> header,
it is passed through unchanged.</li>
<li>If set to <code>On</code>, each request and reply will get a
<code>Via:</code> header line added for the current host.</li>
<li>If set to <code>Full</code>, each generated <code>Via:</code> header
line will additionally have the Apache httpd server version shown as a
<code>Via:</code> comment field.</li>
<li>If set to <code>Block</code>, every proxy request will have all its
<code>Via:</code> header lines removed. No new <code>Via:</code> header will
be generated.</li>
</ul>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyErrorOverride</name>
<description>Override error pages for proxied content</description>
<syntax>ProxyErrorOverride On|Off</syntax>
<default>ProxyErrorOverride Off</default>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>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
<module>mod_include</module>'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).</p>
<p>This directive does not affect the processing of informational (1xx),
normal success (2xx), or redirect (3xx) responses.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyPassInterpolateEnv</name>
<description>Enable Environment Variable interpolation in Reverse Proxy configurations</description>
<syntax>ProxyPassInterpolateEnv On|Off</syntax>
<default>ProxyPassInterpolateEnv Off</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>This directive, together with the <var>interpolate</var> argument to
<directive>ProxyPass</directive>, <directive>ProxyPassReverse</directive>,
<directive>ProxyPassReverseCookieDomain</directive> and
<directive>ProxyPassReverseCookiePath</directive>
enables reverse proxies to be dynamically
configured using environment variables, which may be set by
another module such as <module>mod_rewrite</module>.
It affects the <directive>ProxyPass</directive>,
<directive>ProxyPassReverse</directive>,
<directive>ProxyPassReverseCookieDomain</directive>, and
<directive>ProxyPassReverseCookiePath</directive> directives,
and causes them to substitute the value of an environment
variable <code>varname</code> for the string <code>${varname}</code>
in configuration directives (if the <var>interpolate</var> option is set).</p>
<p>Keep this turned off (for server performance) unless you need it!</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyStatus</name>
<description>Show Proxy LoadBalancer status in mod_status</description>
<syntax>ProxyStatus Off|On|Full</syntax>
<default>ProxyStatus Off</default>
<contextlist><context>server config</context>
<context>virtual host</context>
</contextlist>
<usage>
<p>This directive determines whether or not proxy
loadbalancer status data is displayed via the <module>mod_status</module>
server-status page.</p>
<note><title>Note</title>
<p><strong>Full</strong> is synonymous with <strong>On</strong></p>
</note>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyAddHeaders</name>
<description>Add proxy information in X-Forwarded-* headers</description>
<syntax>ProxyAddHeaders Off|On</syntax>
<default>ProxyAddHeaders On</default>
<contextlist><context>server config</context>
<context>virtual host</context>
<context>directory</context>
</contextlist>
<compatibility>Available in version 2.3.10 and later</compatibility>
<usage>
<p>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.</p>
<note><title>Effectiveness</title>
<p>This option is of use only for HTTP proxying, as handled by <module>mod_proxy_http</module>.</p>
</note>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxySourceAddress</name>
<description>Set local IP address for outgoing proxy connections</description>
<syntax>ProxySourceAddress <var>address</var></syntax>
<contextlist><context>server config</context>
<context>virtual host</context>
</contextlist>
<compatibility>Available in version 2.3.9 and later</compatibility>
<usage>
<p>This directive allows to set a specific local address to bind to when connecting
to a backend server.</p>
</usage>
</directivesynopsis>
</modulesynopsis>