mod_proxy.xml revision 715abc2963d95c317736885f4153bb0dcb22abfc
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<modulesynopsis metafile="mod_proxy.xml.meta">
<name>mod_proxy</name>
<status>Extension</status>
<identifier>proxy_module</identifier>
<summary>
<note type="warning"><title>Warning</title>
<p>Do not enable proxying with <directive module="mod_proxy"
>ProxyRequests</directive> until you have <a href="#access"
>secured your server</a>. Open proxy servers are dangerous both to your
network and to the Internet at large.</p>
</note>
proxying capability for <code>AJP13</code> (Apache JServe Protocol
version 1.3), <code>FTP</code>, <code>CONNECT</code> (for SSL),
The module can be configured to connect to other proxy modules for these
and other protocols.</p>
<p>Apache's proxy features are divided into several modules in
addition to <module>mod_proxy</module>:
<module>mod_proxy_http</module>, <module>mod_proxy_ftp</module>,
<module>mod_proxy_ajp</module>, <module>mod_proxy_balancer</module>,
and <module>mod_proxy_connect</module>. Thus, if you want to use
one or more of the particular proxy functions, load
<module>mod_proxy</module> <em>and</em> the appropriate module(s)
into the server (either statically at compile-time or dynamically
via the <directive module="mod_so">LoadModule</directive>
directive).</p>
<p>In addition, extended features are provided by other modules.
Caching is provided by <module>mod_cache</module> and related
protocol is provided by the <code>SSLProxy*</code> directives of
<module>mod_ssl</module>. These additional modules will need
to be loaded and configured to take advantage of these features.</p>
</summary>
<seealso><module>mod_cache</module></seealso>
<seealso><module>mod_proxy_http</module></seealso>
<seealso><module>mod_proxy_ftp</module></seealso>
<seealso><module>mod_proxy_connect</module></seealso>
<seealso><module>mod_ssl</module></seealso>
<section id="forwardreverse"><title>Forward and Reverse Proxies</title>
<p>Apache can be configured in both a <dfn>forward</dfn> and
<dfn>reverse</dfn> proxy mode.</p>
<p>An ordinary <dfn>forward proxy</dfn> is an intermediate
server that sits between the client and the <em>origin
server</em>. In order to get content from the origin server,
the client sends a request to the proxy naming the origin server
as the target and the proxy then requests the content from the
origin server and returns it to the client. The client must be
specially configured to use the forward proxy to access other
sites.</p>
<p>A typical usage of a forward proxy is to provide Internet
access to internal clients that are otherwise restricted by a
firewall. The forward proxy can also use caching (as provided
by <module>mod_cache</module>) to reduce network usage.</p>
<p>The forward proxy is activated using the <directive
module="mod_proxy">ProxyRequests</directive> directive. Because
forward proxys 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>, by contrast, appears to the
client just like an ordinary web server. No special
configuration on the client is necessary. The client makes
ordinary requests for content in the name-space of the reverse
proxy. The reverse proxy then decides where to send those
requests, and returns the content as if it was itself the
origin.</p>
<p>A typical usage of a reverse proxy is to provide Internet
users access to a server that is behind a firewall. Reverse
proxies can also be used to balance load among several back-end
servers, or to provide caching for a slower back-end server.
In addition, reverse proxies can be used simply to bring
several servers into the same URL space.</p>
<p>A reverse proxy is activated using the <directive
module="mod_proxy">ProxyPass</directive> directive or the
<code>[P]</code> flag to the <directive
module="mod_rewrite">RewriteRule</directive> directive. It is
<strong>not</strong> necessary to turn <directive
module="mod_proxy">ProxyRequests</directive> on in order to
configure a reverse proxy.</p>
</section> <!-- /forwardreverse -->
<section id="examples"><title>Basic Examples</title>
<p>The examples below are only a very basic idea to help you
get started. Please read the documentation on the individual
directives.</p>
<p>In addition, if you wish to have caching enabled, consult
the documentation from <module>mod_cache</module>.</p>
<example><title>Forward Proxy</title>
ProxyRequests On<br />
ProxyVia On<br />
<br />
<Proxy *><br />
<indent>
Order deny,allow<br />
Deny from all<br />
Allow from internal.example.com<br />
</indent>
</Proxy>
</example>
<example><title>Reverse Proxy</title>
ProxyRequests Off<br />
<br />
<Proxy *><br />
<indent>
Order deny,allow<br />
Allow from all<br />
</indent>
</Proxy><br />
<br />
ProxyPass /foo http://foo.example.com/bar<br />
ProxyPassReverse /foo http://foo.example.com/bar
</example>
</section> <!-- /examples -->
<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>
<example>
<Proxy *><br />
<indent>
Order Deny,Allow<br />
Deny from all<br />
Allow from 192.168.0<br />
</indent>
</Proxy>
</example>
<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>
</section> <!-- /access -->
<section id="ftp-proxy"><title>FTP Proxy</title>
<section id="mimetypes"><title>Why doesn't file type <var>xxx</var>
download via FTP?</title>
<p>You probably don't have that particular file type defined as
configuration file. A useful line can be</p>
<example>
</example>
<p>Alternatively you may prefer to default everything to binary:</p>
<example>
</example>
</section> <!-- /mimetypes -->
<section id="type"><title>How can I force an FTP ASCII download of
File <var>xxx</var>?</title>
<p>In the rare situation where you must download a specific file using the
FTP <code>ASCII</code> transfer method (while the default transfer is in
<code>binary</code> mode), you can override <module>mod_proxy</module>'s
default by suffixing the request with <code>;type=a</code> to force an
ASCII transfer. (FTP Directory listings are always executed in ASCII mode,
however.)</p>
</section> <!-- /type -->
<section id="ftpnonget"><title>How can I do FTP upload?</title>
<p>Currently, only GET is supported for FTP in mod_proxy. You can
of course use HTTP upload (POST or PUT) through an Apache proxy.</p>
</section>
<section id="percent2fhck"><title>How can I access FTP files outside
of my home directory?</title>
<p>An FTP URI is interpreted relative to the home directory of the user
who is logging in. Alas, to reach higher directory levels you cannot
use /../, as the dots are interpreted by the browser and not actually
sent to the FTP server. To address this problem, the so called <dfn>Squid
%2f hack</dfn> was implemented in the Apache FTP proxy; it is a
solution which is also used by other popular proxy servers like the <a
href="http://www.squid-cache.org/">Squid Proxy Cache</a>. By
prepending <code>/%2f</code> to the path of your request, you can make
such a proxy change the FTP starting directory to <code>/</code> (instead
of the home directory). For example, to retrieve the file
<example>
</example>
</section> <!-- /percent2fhck -->
<section id="ftppass"><title>How can I hide the FTP cleartext password
in my browser's URL line?</title>
<p>To log in to an FTP server by username and password, Apache uses
different strategies. In absense of a user name and password in the URL
altogether, Apache sends an anonymous login to the FTP server,
<example>
user: anonymous<br />
password: apache_proxy@
</example>
<p>This works for all popular FTP servers which are configured for
anonymous access.</p>
<p>For a personal login with a specific username, you can embed the user
name into the URL, like in:</p>
<example>
ftp://<var>username</var>@<var>host</var>/myfile
</example>
<p>If the FTP server asks for a password when given this username (which
it should), then Apache will reply with a <code>401</code> (Authorization
required) response, which causes the Browser to pop up the
attempt is retried, and if successful, the requested resource is
presented. The advantage of this procedure is that your browser does not
display the password in cleartext (which it would if you had used</p>
<example>
ftp://<var>username</var>:<var>password</var>@<var>host</var>/myfile
</example>
<p>in the first place).</p>
<note><title>Note</title>
<p>The password which is transmitted in such a way is not encrypted on
its way. It travels between your browser and the Apache proxy server in
a base64-encoded cleartext string, and between the Apache proxy and the
FTP server as plaintext. You should therefore think twice before
accessing your FTP server via HTTP (or before accessing your personal
files via FTP at all!) When using unsecure channels, an eavesdropper
might intercept your password on its way.</p>
</note>
</section> <!-- /ftppass -->
</section> <!-- /ftpproxy -->
<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 proxy server situated in an intranet needs to forward
external requests through the company's firewall (for this, configure
the <directive module="mod_proxy">ProxyRemote</directive> directive
to forward the respective <var>scheme</var> to the firewall proxy).
However, when it has to
access resources within the intranet, it can bypass the firewall when
accessing hosts. The <directive module="mod_proxy">NoProxy</directive>
directive is useful for specifying which hosts belong to the intranet and
should be accessed directly.</p>
<p>Users within an intranet tend to omit the local domain name from their
WWW requests, thus requesting "http://somehost/" instead of
let them get away with this and simply serve the request, implying a
configured local domain. When the <directive module="mod_proxy"
>ProxyDomain</directive> directive is used and the server is <a
href="#proxyrequests">configured for proxy service</a>, Apache 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 you have a application server which doesn't
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>
<example>
<Location /buggyappserver/><br />
<indent>
ProxyPass http://buggyappserver:7001/foo/<br />
SetEnv force-proxy-request-1.0 1<br />
SetEnv proxy-nokeepalive 1<br />
</indent>
</Location>
</example>
</section> <!-- /envsettings -->
<directivesynopsis type="section">
<name>Proxy</name>
<description>Container for directives applied to proxied resources</description>
<syntax><Proxy <var>wildcard-url</var>> ...</Proxy></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>Directives placed in <directive type="section">Proxy</directive>
sections apply only to matching proxied content. Shell-style wildcards are
allowed.</p>
<p>For example, the following will allow only hosts in
server:</p>
<example>
<Proxy *><br />
<indent>
Order Deny,Allow<br />
Deny from all<br />
Allow from yournetwork.example.com<br />
</indent>
</Proxy>
</example>
<p>The following example will process all files in the <code>foo</code>
filter when they are sent through the proxy server:</p>
<example>
<Proxy http://example.com/foo/*><br />
<indent>
SetOutputFilter INCLUDES<br />
</indent>
</Proxy>
</example>
</usage>
</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>
<compatibility>available in Apache 2.0.44 and later</compatibility>
<usage>
<p>The <directive>ProxyBadHeader</directive> directive determines the
behaviour of <module>mod_proxy</module> if it receives syntactically invalid
are possible:</p>
<dl>
<dt><code>IsError</code></dt>
<dd>Abort the request and end up with a 502 (Bad Gateway) response. This is
the default behaviour.</dd>
<dt><code>Ignore</code></dt>
<dd>Treat bad header lines as if they weren't sent.</dd>
<dt><code>StartBody</code></dt>
<dd>When receiving the first bad header line, finish reading the headers and
treat the remainder as body. This helps to work around buggy backend servers
which forget to insert an empty line between the headers and the body.</dd>
</dl>
</usage>
</directivesynopsis>
<directivesynopsis type="section">
<name>ProxyMatch</name>
<description>Container for directives applied to regular-expression-matched
proxied resources</description>
<syntax><ProxyMatch <var>regex</var>> ...</ProxyMatch></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive type="section">ProxyMatch</directive> directive is
identical to the <directive module="mod_proxy"
type="section">Proxy</directive> directive, except it matches URLs
using regular expressions.</p>
</usage>
</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>
</contextlist>
<compatibility>Available in Apache 2.0.31 and later.</compatibility>
<usage>
<p>When enabled, this option will pass the Host: line from the incoming
request to the proxied host, instead of the hostname specified in the
<directive>ProxyPass</directive> line.</p>
<p>This option should normally be turned <code>Off</code>. It is mostly
useful in special configurations like proxied mass name-based virtual
hosting, where the original Host header needs to be evaluated by the
backend server.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyRequests</name>
<description>Enables forward (standard) proxy requests</description>
<syntax>ProxyRequests On|Off</syntax>
<default>ProxyRequests Off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This allows or prevents Apache 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 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>
<note type="warning"><title>Warning</title>
<p>Do not enable proxying with <directive
module="mod_proxy">ProxyRequests</directive> until you have <a
href="#access">secured your server</a>. Open proxy servers are dangerous
both to your network and to the Internet at large.</p>
</note>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyRemote</name>
<description>Remote proxy used to handle certain requests</description>
<syntax>ProxyRemote <var>match</var> <var>remote-server</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This defines remote proxies to this proxy. <var>match</var> is either the
name of a URL-scheme that the remote server supports, or a partial URL
for which the remote server should be used, or <code>*</code> to indicate
the server should be contacted for all requests. <var>remote-server</var> is
a partial URL for the remote server. Syntax:</p>
<example>
<dfn>remote-server</dfn> =
<var>scheme</var>://<var>hostname</var>[:<var>port</var>]
</example>
<p><var>scheme</var> is effectively the protocol that should be used to
communicate with the remote server; only <code>http</code> is supported by
this module.</p>
<example><title>Example</title>
ProxyRemote * http://cleversite.com<br />
ProxyRemote ftp http://ftpproxy.mydomain.com:8080
</example>
<p>In the last example, the proxy will forward FTP requests, encapsulated
as yet another HTTP proxy request, to another proxy which can handle
them.</p>
<p>This option also supports reverse proxy configuration - a backend
webserver can be embedded within a virtualhost URL space even if that
server is hidden by another forward proxy.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyRemoteMatch</name>
<description>Remote proxy used to handle requests matched by regular
expressions</description>
<syntax>ProxyRemoteMatch <var>regex</var> <var>remote-server</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyRemoteMatch</directive> is identical to the
<directive module="mod_proxy">ProxyRemote</directive> directive, except the
first argument is a regular expression match against the requested URL.</p>
</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></syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>This directive allows remote servers to be mapped into the space of
the local server; the local server does not act as a proxy in the
conventional sense, but appears to be a mirror of the remote
server. <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>
then</p>
<example>
</example>
<p>will cause a local request for
<p>The <code>!</code> directive is useful in situations where you don't want
<example>
</example>
<note><title>Note</title>
<p>Order is important. you need to put the exclusions <em>before</em> the
general <directive>ProxyPass</directive> directive.</p>
</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>.</p>
<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>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>
</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></syntax>
<contextlist><context>server config</context><context>virtual host</context>
<context>directory</context>
</contextlist>
<usage>
<p>This directive lets Apache 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 is used as a reverse proxy to avoid
by-passing the reverse proxy because of HTTP redirects on the backend
servers which stay behind the reverse proxy.</p>
<p>Only the HTTP response headers specifically mentioned above
will be rewritten. Apache will not rewrite other response
headers, nor will it rewrite URL references inside HTML pages.
This means that if the proxied content contains absolute URL
references, they will by-pass the proxy. A third-party module
that will look inside the HTML and rewrite URL references is Nick
Kew's <a href="http://apache.webthing.com/software/mod_proxy_html/"
>mod_proxy_html</a>.</p>
<p><var>path</var> is the name of a local virtual path. <var>url</var> is a
partial URL for the remote server - the same way they are used for the
<directive module="mod_proxy">ProxyPass</directive> directive.</p>
<p>For example, suppose the local server has address
<example>
</example>
<p>will not only cause a local request for the
(the functionality <code>ProxyPass</code> provides here). It also takes care
redirect response to the client. Note that the hostname used for
constructing the URL is chosen in respect to the setting of the <directive
module="core">UseCanonicalName</directive> directive.</p>
<p>Note that this <directive>ProxyPassReverse</directive> directive can
also be used in conjunction with the proxy pass-through feature
(<code>RewriteRule ... [P]</code>) from <module>mod_rewrite</module>
because its doesn't depend on a corresponding <directive module="mod_proxy"
>ProxyPass</directive> directive.</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>.</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></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></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>path</code>
string in <code>Set-Cookie</code> headers.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>AllowCONNECT</name>
<description>Ports that are allowed to <code>CONNECT</code> through the
proxy</description>
<syntax>AllowCONNECT <var>port</var> [<var>port</var>] ...</syntax>
<default>AllowCONNECT 443 563</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>AllowCONNECT</directive> directive specifies a list
of port numbers to which the proxy <code>CONNECT</code> method may
connect. Today's browsers use this method when a <code>https</code>
connection is requested and proxy tunneling over HTTP is in effect.</p>
<p>By default, only the default https port (<code>443</code>) and the
default snews port (<code>563</code>) are enabled. Use the
<directive>AllowCONNECT</directive> directive to override this default and
allow connections to the listed ports only.</p>
<p>Note that you'll need to have <module>mod_proxy_connect</module> present
in the server in order to get the support for the <code>CONNECT</code> at
all.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyBlock</name>
<description>Words, hosts, or domains that are banned from being
proxied</description>
<syntax>ProxyBlock *|<var>word</var>|<var>host</var>|<var>domain</var>
[<var>word</var>|<var>host</var>|<var>domain</var>] ...</syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyBlock</directive> directive specifies a list of
FTP document requests to sites whose names contain matched words,
hosts or domains are <em>blocked</em> by the proxy server. The proxy
module will also attempt to determine IP addresses of list items which
may be hostnames during startup, and cache them for match test as
well. That may slow down the startup time of the server.</p>
<example><title>Example</title>
</example>
IP address.</p>
<p>Note that <code>wotsamattau</code> would also be sufficient to match
<p>Note also that</p>
<example>
ProxyBlock *
</example>
<p>blocks connections to all sites.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyReceiveBufferSize</name>
<description>Network buffer size for proxied HTTP and FTP
connections</description>
<syntax>ProxyReceiveBufferSize <var>bytes</var></syntax>
<default>ProxyReceiveBufferSize 0</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>The <directive>ProxyReceiveBufferSize</directive> directive specifies an
for increased throughput. It has to be greater than <code>512</code> or set
to <code>0</code> to indicate that the system's default buffer size should
be used.</p>
<example><title>Example</title>
ProxyReceiveBufferSize 2048
</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 less or equal <code>8192</code>.</p>
<p>In almost every case there's no reason to change that value.</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 10</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<compatibility>Available in Apache 2.0 and later</compatibility>
<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 is
set to prevent infinite proxy loops, or a DoS attack.</p>
<example><title>Example</title>
ProxyMaxForwards 15
</example>
</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 proxy servers within
intranets. The <directive>NoProxy</directive> directive specifies a
spaces. A request to a host which matches one or more of these is
always served directly, without forwarding to the configured
<directive module="mod_proxy">ProxyRemote</directive> proxy server(s).</p>
<example><title>Example</title>
ProxyRemote * http://firewall.mycompany.com:81<br />
</example>
<p>The <var>host</var> arguments to the <directive>NoProxy</directive>
directive are one of the following type list:</p>
<dl>
<!-- ===================== Domain ======================= -->
<dt><var><a name="domain" id="domain">Domain</a></var></dt>
<dd>
<p>A <dfn>Domain</dfn> is a partially qualified DNS domain name, preceded
by a period. It represents a list of hosts which logically belong to the
all ending in <var>Domain</var>).</p>
<example><title>Examples</title>
.com .apache.org.
</example>
<p>To distinguish <var>Domain</var>s from <var><a href="#hostname"
>Hostname</a></var>s (both syntactically and semantically; a DNS domain can
have a DNS A record, too!), <var>Domain</var>s are always written with a
leading period.</p>
<note><title>Note</title>
<p>Domain name comparisons are done without regard to the case, and
<var>Domain</var>s are always assumed to be anchored in the root of the
equal. Since a domain comparison does not involve a DNS lookup, it is much
more efficient than subnet comparison.</p>
</note></dd>
<!-- ===================== SubNet ======================= -->
<dt><var><a name="subnet" id="subnet">SubNet</a></var></dt>
<dd>
<p>A <dfn>SubNet</dfn> is a partially qualified internet address in
numeric (dotted quad) form, optionally followed by a slash and the netmask,
specified as the number of significant bits in the <var>SubNet</var>. It is
used to represent a subnet of hosts which can be reached over a common
network interface. In the absence of the explicit net mask it is assumed
that omitted (or zero valued) trailing digits specify the mask. (In this
case, the netmask can only be multiples of 8 bits wide.) Examples:</p>
<dl>
<dt><code>192.168</code> or <code>192.168.0.0</code></dt>
<dd>the subnet 192.168.0.0 with an implied netmask of 16 valid bits
(sometimes used in the netmask form <code>255.255.0.0</code>)</dd>
valid bits (also used in the form <code>255.255.248.0</code>)</dd>
</dl>
<p>As a degenerate case, a <em>SubNet</em> with 32 valid bits is the
equivalent to an <var><a href="#ipadr">IPAddr</a></var>, while a <var>SubNet</var> with zero
<var>_Default_</var>, matching any IP address.</p></dd>
<!-- ===================== IPAddr ======================= -->
<dt><var><a name="ipaddr" id="ipaddr">IPAddr</a></var></dt>
<dd>
<p>A <dfn>IPAddr</dfn> represents a fully qualified internet address in
numeric (dotted quad) form. Usually, this address represents a host, but
there need not necessarily be a DNS domain name connected with the
address.</p>
<example><title>Example</title>
192.168.123.7
</example>
<note><title>Note</title>
<p>An <var>IPAddr</var> does not need to be resolved by the DNS system, so
it can result in more effective apache performance.</p>
</note></dd>
<!-- ===================== Hostname ======================= -->
<dt><var><a name="hostname" id="hostname">Hostname</a></var></dt>
<dd>
<p>A <dfn>Hostname</dfn> is a fully qualified DNS domain name which can
be resolved to one or more <var><a href="#ipaddr">IPAddrs</a></var> via the
DNS domain name service. It represents a logical host (in contrast to
<var><a href="#domain">Domain</a></var>s, see above) and must be resolvable
to at least one <var><a href="#ipaddr">IPAddr</a></var> (or often to a list
of hosts with different <var><a href="#ipaddr">IPAddr</a></var>s).</p>
<example><title>Examples</title>
prep.ai.mit.edu<br />
</example>
<note><title>Note</title>
<p>In many situations, it is more effective to specify an <var><a
href="#ipaddr">IPAddr</a></var> in place of a <var>Hostname</var> since a
DNS lookup can be avoided. Name resolution in Apache can take a remarkable
deal of time when the connection to the name server uses a slow PPP
link.</p>
<p><var>Hostname</var> comparisons are done without regard to the case,
and <var>Hostname</var>s are always assumed to be anchored in the root
considered equal.</p>
</note></dd>
</dl>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyTimeout</name>
<description>Network timeout for proxied requests</description>
<syntax>ProxyTimeout <var>seconds</var></syntax>
<default>ProxyTimeout 300</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<compatibility>Available in Apache 2.0.31 and later</compatibility>
<usage>
<p>This directive allows a user to specifiy a timeout on proxy requests.
would rather just return a timeout and fail gracefully instead of waiting
however long it takes the server to return.</p>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyDomain</name>
<description>Default domain name for proxied requests</description>
<syntax>ProxyDomain <var>Domain</var></syntax>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This directive is only useful for Apache 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>
ProxyRemote * http://firewall.mycompany.com:81<br />
ProxyDomain .mycompany.com
</example>
</usage>
</directivesynopsis>
<directivesynopsis>
<name>ProxyVia</name>
<description>Information provided in the <code>Via</code> HTTP response
header for proxied requests</description>
<syntax>ProxyVia On|Off|Full|Block</syntax>
<default>ProxyVia Off</default>
<contextlist><context>server config</context><context>virtual host</context>
</contextlist>
<usage>
<p>This directive controls the use of the <code>Via:</code> HTTP
header by the proxy. Its intended use is to control the flow of
proxy requests along a chain of proxy servers. See <a
14.45 for an explanation of <code>Via:</code> header lines.</p>
<ul>
<li>If set to <code>Off</code>, which is the default, no special processing
is performed. If a request or reply contains a <code>Via:</code> header,
it is passed through unchanged.</li>
<li>If set to <code>On</code>, each request and reply will get a
<code>Via:</code> header line added for the current host.</li>
<li>If set to <code>Full</code>, each generated <code>Via:</code> header
line will additionally have the Apache 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>
</contextlist>
<compatibility>Available in version 2.0 and later</compatibility>
<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>
</usage>
</directivesynopsis>
</modulesynopsis>