apache/docs/manual/mod/mod_proxy.xml

<?xml version="1.0"?>
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
<!-- $LastChangedRevision$ -->

<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->

<modulesynopsis metafile="mod_proxy.xml.meta">

<name>mod_proxy</name>
<description>Multi-protocol proxy/gateway server</description>
<status>Extension</status>
<sourcefile>mod_proxy.c</sourcefile>
<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
    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.</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>HTTP/0.9, HTTP/1.0, and
          HTTP/1.1</td><td><module>mod_proxy_http</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
    modules.  The ability to contact remote servers using the SSL/TLS
    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_balancer</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_hcheck</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_ssl</module></seealso>

    <section id="forwardreverse"><title>Forward Proxies and Reverse
       Proxies/Gateways</title>
      <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. 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 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.</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

&lt;Proxy *&gt;
  Require host internal.example.com
&lt;/Proxy&gt;
    </highlight>
    </example>
    </section> <!-- /examples -->

    <section id="handler"><title>Access via Handler</title>

      <p>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:
      </p>

      <example><title>Reverse Proxy PHP scripts</title>
      <highlight language="config">
&lt;FilesMatch "\.php$"&gt;
    SetHandler  "proxy:unix:/path/to/app.sock|fcgi://localhost/"
&lt;/FilesMatch&gt;
      </highlight>
      </example>

      <p>This feature is available in Apache HTTP Server 2.4.10 and later.</p>

    </section> <!-- /handler -->

    <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 reuse.
      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
      <code>http://backend.example.com</code> that will use the given timeout
      values. All timeouts use the <a href="directive-dict.html#Syntax">time-interval</a>
      directive syntax. 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">
&lt;Proxy http://backend.example.com&gt;
  ProxySet connectiontimeout=5 timeout=30
&lt;/Proxy&gt;
      </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 also be 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 -->

      <note type="warning"><title>Host part in the URL</title>
        <p>The host part needs to start with a letter [a-z]. For example:</p>
        <highlight language="config">
ProxyPass "/apps"     "http://127"
        </highlight>
        <p>is not valid and will cause an error while processing a request that
        maps the path.</p>
      </note>

      <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>

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

    </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">
&lt;Proxy *&gt;
  Require ip 192.168.0
&lt;/Proxy&gt;
      </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>

      <p><strong>See Also</strong> the <a href="mod_proxy_http.html#env"
      >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
      <code>http://somehost.example.com/</code>. Some commercial proxy servers
      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
      keepalives or HTTP/1.1, there are two <a
      href="../env.html">environment variables</a> that can force the
      request to use HTTP/1.0 with no keepalive. These are set via 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">
&lt;Location "/buggyappserver/"&gt;
  ProxyPass "http://buggyappserver:7001/foo/"
  SetEnv force-proxy-request-1.0 1
  SetEnv proxy-nokeepalive 1
&lt;/Location&gt;
        </highlight>

      <p> In 2.4.26 and later, the "no-proxy" environment variable can be set to disable 
      <module>mod_proxy</module> processing the current request.
      This variable should be set with <directive module="mod_setenvif"
      >SetEnvIf</directive>, as <directive module="mod_env">SetEnv</directive>
      is not evaluated early enough.</p>

    </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
    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.</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>

    <p>Note:  If you need to specify custom request headers to be
    added to the forwarded request, use the
    <directive module="mod_headers">RequestHeader</directive>
    directive.</p>

   </section> <!--/x-headers -->


<directivesynopsis type="section">
<name>Proxy</name>
<description>Container for directives applied to proxied resources</description>
<syntax>&lt;Proxy <var>wildcard-url</var>&gt; ...&lt;/Proxy&gt;</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
    <code>yournetwork.example.com</code> to access content via your proxy
    server:</p>

    <highlight language="config">
&lt;Proxy *&gt;
  Require host yournetwork.example.com
&lt;/Proxy&gt;
    </highlight>

    <p>The following example will process all files in the <code>foo</code>
    directory of <code>example.com</code> through the <code>INCLUDES</code>
    filter when they are sent through the proxy server:</p>

   <highlight language="config">
&lt;Proxy http://example.com/foo/*&gt;
  SetOutputFilter INCLUDES
&lt;/Proxy&gt;
    </highlight>

    <p>The next example will allow web clients from the specified IP
    addresses to issue <code>CONNECT</code> requests to access the
    <code>https://www.example.com/</code> SSL server if
    <module>mod_proxy_connect</module> is enabled.
    </p>

   <highlight language="config">
&lt;Proxy www.example.com:443&gt;
  Require ip 192.168.0.0/16
&lt;/Proxy&gt;
   </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,
      &lt;Proxy http://example.com/foo&gt; matches all of
      http://example.com/foo, http://example.com/foo/bar, and
      http://example.com/foobar.  The matching of the final URL differs
      from the behavior of the <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
    behavior of <module>mod_proxy</module> if it receives syntactically invalid
    response header lines (<em>i.e.</em> containing no colon) from the origin
    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 behavior.</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>&lt;ProxyMatch <var>regex</var>&gt; ...&lt;/ProxyMatch&gt;</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 that it matches URLs
    using <glossary ref="regex">regular expressions</glossary>.</p>

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

<highlight language="config">
&lt;ProxyMatch ^http://(?&lt;sitename&gt;[^/]+)&gt;
    require ldap-group cn=%{env:MATCH_SITENAME},ou=combined,o=Example
&lt;/ProxyMatch&gt;
</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 module="mod_proxy">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>
<seealso><a href="#forwardreverse">Forward and Reverse Proxies/Gateways</a></seealso>
</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://goodguys.example.com/ http://mirrorguys.example.com:8000
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 that
    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 one 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 2.4.4 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
        normal restart/graceful state transitions.</p>
    </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 2.4.5 and later.
        </compatibility>
    <usage>
        <p>This directive will cause the current server/vhost to "inherit"
            <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>
    <description>Inherit proxy Balancers/Workers defined from the main server</description>
    <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 2.4.5 and later.</compatibility>
    <usage>
        <p>This directive will cause the current server/vhost to "inherit"
            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 can be used
            within a <code>&lt;Proxy <var>balancer://</var>...&gt;</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>BalancerMember</directive> directives:
            <var>loadfactor</var>. This is the member load factor - a decimal between 1.0
            (default) and 100.0, which defines the weighted load to be applied to the
            member in question.</p>
        <p>The <var>balancerurl</var> is only needed when not within a
            <code>&lt;Proxy <var>balancer://</var>...&gt;</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>&lt;Proxy <var>balancer://</var>...&gt;</code> container directive
            is ignored.</p>
        <p>Trailing slashes should typically be removed from the URL of a
            <directive>BalancerMember</directive>.</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>&lt;Proxy <var>balancer url|worker url</var>&gt;</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">
&lt;Proxy balancer://hotcluster&gt;
    BalancerMember http://www2.example.com:8080 loadfactor=1
    BalancerMember http://www3.example.com:8080 loadfactor=2
    ProxySet lbmethod=bytraffic
&lt;/Proxy&gt;
      </highlight>
    </example>

    <highlight language="config">
&lt;Proxy http://backend&gt;
    ProxySet keepalive=On
&lt;/Proxy&gt;
    </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>
<compatibility>Unix Domain Socket (UDS) support added in 2.4.7</compatibility>

<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>It is strongly suggested to review the concept of a
    <a href="#workers">Worker</a> before proceeding any further
    with this section.</note>

    <note>This directive is not supported within
    <directive type="section" module="core">Directory</directive> and
    <directive type="section" module="core">Files</directive> containers.</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>In 2.4.7 and later, support for using a Unix Domain Socket is available by using a target
    which prepends <code>unix:/path/lis.sock|</code>. For example, to proxy
    HTTP and target the UDS at /home/www/socket, you would use
    <code>unix:/home/www.socket|http://localhost/whatever/</code>. Since
    the socket is local, the hostname used (in this case <code>localhost</code>)
    is moot, but it is passed as the Host: header value of the request.</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>

    <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>Suppose the local server has address <code>http://example.com/</code>;
    then</p>

    <highlight language="config">
&lt;Location "/mirror/foo/"&gt;
    ProxyPass "http://backend.example.com/"
&lt;/Location&gt;
    </highlight>

    <p>will cause a local request for
    <code>http://example.com/mirror/foo/bar</code> to be internally converted
    into a proxy request to <code>http://backend.example.com/bar</code>.</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 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
    <a href="mod_proxy_balancer.html#balancer_manager">Balancer Manager</a> interface:</p>

    <highlight language="config">
        ProxyPass "/mirror/foo/" "http://backend.example.com/"
    </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
    to reverse-proxy a subdirectory, <em>e.g.</em></p>

    <highlight language="config">
&lt;Location "/mirror/foo/"&gt;
    ProxyPass "http://backend.example.com/"
&lt;/Location&gt;
&lt;Location "/mirror/foo/i"&gt;
    ProxyPass "!"
&lt;/Location&gt;
    </highlight>

    <highlight language="config">
ProxyPass "/mirror/foo/i" "!"
ProxyPass "/mirror/foo"   "http://backend.example.com"
    </highlight>

    <p>will proxy all requests to <code>/mirror/foo</code> to
    <code>backend.example.com</code> <em>except</em> requests made to
    <code>/mirror/foo/i</code>.</p>

    <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. In 2.4.26 and later, the "no-proxy"
      environment variable is an alternative to exclusions, and is the only
      way to configure an exclusion of a <directive>ProxyPass</directive>
      directive in <directive module="core">Location</directive> context. 
      This variable should be set with <directive module="mod_setenvif"
      >SetEnvIf</directive>, as <directive module="mod_env">SetEnv</directive>
      is not evaluated early enough.
      </p>

    </note> <!-- /ordering_proxypass -->

    <p><strong>ProxyPass <code>key=value</code> Parameters</strong></p>

    <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 tables
    below.</p>

    <note type="warning"><title>Maximum connections to the backend</title>
    <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. 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>
    </note>

    <p>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>

    <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>Worker|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>1...n</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. Uses the <a href="directive-dict.html#Syntax">time-interval</a> directive syntax
    </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.
    When connection reuse is enabled each backend domain is resolved
    (with a DNS query) only once per child process and cached for all further
    connections until the child is recycled. To disable connection reuse,
    set this property value to <code>On</code>.
    </td></tr>
    <tr><td>enablereuse</td>
        <td>On</td>
        <td>This is the inverse of 'disablereuse' above, provided as a
        convenience for scheme handlers that require opt-in for connection
        reuse (such as <module>mod_proxy_fcgi</module>).
    </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
        'auto' means poll/wait for a period of time and flush if
        no input has been received for 'flushwait' milliseconds.
        Currently, this is in effect only for mod_proxy_ajp and mod_proxy_fcgi.
    </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'.
        Uses <a href="directive-dict.html#Syntax">time-interval</a> directive syntax.
    </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, which tends 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
    from dropping 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. Uses the <a href="directive-dict.html#Syntax">time-interval</a> directive syntax.</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
        HTTP/1.1 - for non HTTP/1.1 backends, this property has no
        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. Uses the <a href="directive-dict.html#Syntax">time-interval</a> directive syntax.
    </td></tr>
    <tr><td>receivebuffersize</td>
        <td>0</td>
        <td>Adjusts the size of the explicit (TCP/IP) network buffer size for
        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 to 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.
    Uses the <a href="directive-dict.html#Syntax">time-interval</a> directive syntax.
    </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 border="1">
         <tr><td><code>D</code></td><td>Worker is disabled and will not accept any requests; will be
                    automatically retried.</td></tr>
         <tr><td><code>S</code></td><td>Worker is administratively stopped; will not accept requests
                    and will not be automatically retried</td></tr>
         <tr><td><code>I</code></td><td>Worker is in ignore-errors mode and will always be considered available.</td></tr>
         <tr><td><code>H</code></td><td>Worker is in hot-standby mode and will only be used if no other
                    viable workers are available.</td></tr>
         <tr><td><code>E</code></td><td>Worker is in an error state.</td></tr>
         <tr><td><code>N</code></td><td>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.
        Uses the <a href="directive-dict.html#Syntax">time-interval</a> directive syntax.
    </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. Uses the <a href="directive-dict.html#Syntax">time-interval</a> directive syntax.
    </td></tr>
    <tr><td>flusher</td>
        <td>flush</td>
        <td><p>Name of the provider used by <module>mod_proxy_fdpass</module>.
        See the documentation of this module for more details.</p>
    </td></tr>
    <tr><td>secret</td>
        <td>-</td>
        <td><p>Value of secret used by <module>mod_proxy_ajp</module>.
        See the documentation of this module for more details.</p>
    </td></tr>
    <tr><td>upgrade</td>
        <td>WebSocket</td>
        <td><p>Protocol accepted in the Upgrade header by <module>mod_proxy_wstunnel</module>.
        See the documentation of this module for more details.</p>
    </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 added 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. The 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 <code>On</code> 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 names for cookies
        and url encoded id (like servlet containers), use | to separate them.
        The first part is for the cookie; the second is for the path.<br />
        Available in Apache HTTP Server 2.4.4 and later.
    </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
        used as an additional sticky session path delimiter/separator. This
        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. The default is to not wait.
        Uses the <a href="directive-dict.html#Syntax">time-interval</a> directive syntax.
    </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.<br />
        Available in Apache HTTP Server 2.4.5 and later.
    </td></tr>
    <tr><td>nonce</td>
        <td>&lt;auto&gt;</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>.<br />
        Available in Apache HTTP Server 2.4.2 and later.
    </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
&lt;Proxy balancer://mycluster&gt;
    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
&lt;/Proxy&gt;
    </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/"
&lt;Proxy balancer://hotcluster&gt;
    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
&lt;/Proxy&gt;
    </highlight>

    <p><strong>Additional ProxyPass Keywords</strong></p>

    <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 this keyword 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>The optional <var>interpolate</var> keyword, 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]

RewriteRule ^/mirror/foo/(.*) %{ENV:protocol}://backend.example.com/$1 [P]
ProxyPassReverse  "/mirror/foo/" "http://backend.example.com/"
ProxyPassReverse  "/mirror/foo/" "https://backend.example.com/"
    </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>&lt;Directory&gt;</code> context.</note>

    <p>Suppose the local server has address <code>http://example.com/</code>;
    then</p>

    <highlight language="config">
ProxyPassMatch "^/(.*\.gif)$" "http://backend.example.com/$1"
    </highlight>

    <p>will cause a local request for
    <code>http://example.com/foo/bar.gif</code> to be internally converted
    into a proxy request to <code>http://backend.example.com/foo/bar.gif</code>.</p>
    <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>
      <title>Default Substitution</title>
      <p>When the URL parameter doesn't use any backreferences into the regular
      expression, the original URL will be appended to the URL parameter.
      </p>
    </note>

    <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 bypassing 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 bypass 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. These parameters are used the same way as
    for the <directive module="mod_proxy">ProxyPass</directive> directive.</p>

    <p>For example, suppose the local server has address
    <code>http://example.com/</code>; then</p>

    <highlight language="config">
ProxyPass         "/mirror/foo/" "http://backend.example.com/"
ProxyPassReverse  "/mirror/foo/" "http://backend.example.com/"
ProxyPassReverseCookieDomain  backend.example.com  public.example.com
ProxyPassReverseCookiePath  "/"  "/mirror/foo/"
    </highlight>

    <p>will not only cause a local request for the
    <code>http://example.com/mirror/foo/bar</code> to be internally converted
    into a proxy request to <code>http://backend.example.com/bar</code>
    (the functionality which <code>ProxyPass</code> provides here).
    It also takes care of redirects which the server <code>backend.example.com</code> sends
    when redirecting <code>http://backend.example.com/bar</code> to
    <code>http://backend.example.com/quux</code> . Apache httpd adjusts this to
    <code>http://example.com/mirror/foo/quux</code> before forwarding the HTTP
    redirect response to the client. Note that the hostname used for
    constructing the URL is chosen in respect to the setting of the <directive
    module="core">UseCanonicalName</directive> directive.</p>

    <p>Note that this <directive>ProxyPassReverse</directive> directive can
    also be used in conjunction with the proxy 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, 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">
ProxyPassReverseCookiePath  "/"  "/mirror/foo/"
    </highlight>
<p>
will rewrite a cookie with backend path <code>/</code> (or
<code>/example</code> or, in fact, anything) to <code>/mirror/foo/</code>.
</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">
      ProxyBlock news.example.com auctions.example.com friends.example.com
      </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
    explicit (TCP/IP) network buffer size for proxied HTTP and FTP connections,
    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
    violation of the HTTP/1.1 protocol (RFC2616), which forbids a Proxy
    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 behavior 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
    list of subnets, IP addresses, hosts and/or domains, separated by
    spaces. A request to a host which matches one or more of these is
    always served directly, without forwarding to the configured
    <directive module="mod_proxy">ProxyRemote</directive> proxy server(s).</p>

    <example><title>Example</title>
    <highlight language="config">
ProxyRemote  *  http://firewall.example.com:81
NoProxy         .example.com 192.168.112.0/21
    </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
    same DNS domain or zone (<em>i.e.</em>, the suffixes of the hostnames are
    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
      DNS tree; therefore, the two domains <code>.ExAmple.com</code> and
      <code>.example.com.</code> (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.</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>
    <dt><code>192.168.112.0/21</code></dt>
    <dd>the subnet <code>192.168.112.0/21</code> with a netmask of 21
    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
    valid bits (<em>e.g.</em>, 0.0.0.0/0) is the same as the constant
    <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 />
      www.example.org
    </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
      of the DNS tree; therefore, the two hosts <code>WWW.ExAmple.com</code>
      and <code>www.example.com.</code> (note the trailing period) are
      considered equal.</p>
     </note></dd>
    </dl>
</usage>
<seealso><a href="../dns-caveats.html">DNS Issues</a></seealso>
</directivesynopsis>

<directivesynopsis>
<name>ProxyTimeout</name>
<description>Network timeout for proxied requests</description>
<syntax>ProxyTimeout <var>time-interval</var>[s]</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.
    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.</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"
NoProxy           ".example.com" "192.168.112.0/21"
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
    href="http://www.ietf.org/rfc/rfc2616.txt">RFC 2616</a> (HTTP/1.1), section
    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>