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c32c165396
load balancing. Removes a RewriteMap prg load balancing script, and replaces it with a RewriteMap rnd example of the same, as well as an admonition to use mod_proxy_balancer instead. git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@835364 13f79535-47bb-0310-9956-ffa450edef68
191 lines
7.9 KiB
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191 lines
7.9 KiB
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<?xml version="1.0" encoding="ISO-8859-1"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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This file is generated from xml source: DO NOT EDIT
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XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
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-->
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<title>When not to use mod_rewrite - Apache HTTP Server</title>
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<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
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<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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<link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
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<link href="../images/favicon.ico" rel="shortcut icon" /></head>
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<body id="manual-page"><div id="page-header">
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
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<p class="apache">Apache HTTP Server Version 2.3</p>
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<img alt="" src="../images/feather.gif" /></div>
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<div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
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<div id="path">
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Rewrite</a></div><div id="page-content"><div id="preamble"><h1>When not to use mod_rewrite</h1>
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<div class="toplang">
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<p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
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</div>
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<p>This document supplements the <code class="module"><a href="../mod/mod_rewrite.html">mod_rewrite</a></code>
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<a href="../mod/mod_rewrite.html">reference documentation</a>. It provides
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a few advanced techniques and tricks using mod_rewrite.</p>
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<div class="warning">Note that many of these examples won't work unchanged in your
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particular server configuration, so it's important that you understand
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them, rather than merely cutting and pasting the examples into your
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configuration.</div>
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</div>
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<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#sharding">URL-based sharding accross multiple backends</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#on-the-fly-content">On-the-fly Content-Regeneration</a></li>
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<li><img alt="" src="../images/down.gif" /> <a href="#load-balancing">Load Balancing</a></li>
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</ul><h3>See also</h3><ul class="seealso"><li><a href="../mod/mod_rewrite.html">Module documentation</a></li><li><a href="intro.html">mod_rewrite introduction</a></li><li><a href="remapping.html">Redirection and remapping</a></li><li><a href="access.html">Controlling access</a></li><li><a href="avoid.html">When not to use mod_rewrite</a></li></ul></div>
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<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="sharding" id="sharding">URL-based sharding accross multiple backends</a></h2>
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<dl>
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<dt>Description:</dt>
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<dd>
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<p>A common technique for distributing the burden of
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server load or storage space is called "sharding".
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When using this method, a front-end server will use the
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url to consistently "shard" users or objects to separate
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backend servers.</p>
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</dd>
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<dt>Solution:</dt>
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<dd>
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<p>A mapping is maintained, from users to target servers, in
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external map files. They look like:</p>
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<div class="example"><pre>
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user1 physical_host_of_user1
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user2 physical_host_of_user2
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: :
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</pre></div>
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<p>We put this into a <code>map.users-to-hosts</code> file. The
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aim is to map;</p>
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<div class="example"><pre>
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/u/user1/anypath
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</pre></div>
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<p>to</p>
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<div class="example"><pre>
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http://physical_host_of_user1/u/user/anypath
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</pre></div>
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<p>thus every URL path need not be valid on every backend physical
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host. The following ruleset does this for us with the help of the map
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files assuming that server0 is a default server which will be used if
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a user has no entry in the map):</p>
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<div class="example"><pre>
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RewriteEngine on
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RewriteMap users-to-hosts txt:/path/to/map.users-to-hosts
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RewriteRule ^/u/<strong>([^/]+)</strong>/?(.*) http://<strong>${users-to-hosts:$1|server0}</strong>/u/$1/$2
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</pre></div>
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</dd>
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</dl>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="on-the-fly-content" id="on-the-fly-content">On-the-fly Content-Regeneration</a></h2>
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<dl>
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<dt>Description:</dt>
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<dd>
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<p>We wish to dynamically generate content, but store it
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statically once it is generated. This rule will check for the
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existence of the static file, and if it's not there, generate
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it. The static files can be removed periodically, if desired (say,
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via cron) and will be regenerated on demand.</p>
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</dd>
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<dt>Solution:</dt>
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<dd>
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This is done via the following ruleset:
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<div class="example"><pre>
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# This example is valid in per-directory context only
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RewriteCond %{REQUEST_FILENAME} <strong>!-s</strong>
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RewriteRule ^page\.<strong>html</strong>$ page.<strong>cgi</strong> [T=application/x-httpd-cgi,L]
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</pre></div>
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<p>Here a request for <code>page.html</code> leads to an
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internal run of a corresponding <code>page.cgi</code> if
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<code>page.html</code> is missing or has filesize
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null. The trick here is that <code>page.cgi</code> is a
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CGI script which (additionally to its <code>STDOUT</code>)
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writes its output to the file <code>page.html</code>.
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Once it has completed, the server sends out
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<code>page.html</code>. When the webmaster wants to force
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a refresh of the contents, he just removes
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<code>page.html</code> (typically from <code>cron</code>).</p>
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</dd>
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</dl>
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</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
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<div class="section">
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<h2><a name="load-balancing" id="load-balancing">Load Balancing</a></h2>
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<dl>
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<dt>Description:</dt>
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<dd>
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<p>We wish to randomly distribute load across several servers
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using mod_rewrite.</p>
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</dd>
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<dt>Solution:</dt>
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<dd>
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<p>We'll use <code class="directive"><a href="../mod/mod_rewrite.html#rewritemap">RewriteMap</a></code> and a list of servers
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to accomplish this.</p>
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<div class="example"><pre>
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RewriteEngine on
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RewriteMap lb rnd:/path/to/serverlist.txt
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RewriteRule ^/(.*) http://${lb:servers}/$1 [P,L]
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</pre></div>
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<p><code>serverlist.txt</code> will contain a list of the servers:</p>
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<div class="example"><pre>
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## serverlist.txt
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servers one.example.com|two.example.com|three.example.com
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</pre></div>
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<p>If you want one particular server to get more of the load than the
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others, add it more times to the list.</p>
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</dd>
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<dt>Discussion</dt>
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<dd>
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<p>Apache comes with a load-balancing module -
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<code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> - which is far more flexible and
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featureful than anything you can cobble together using mod_rewrite.</p>
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</dd>
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</dl>
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</div></div>
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<div class="bottomlang">
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<p><span>Available Languages: </span><a href="../en/rewrite/avoid.html" title="English"> en </a></p>
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</div><div id="footer">
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<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
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</body></html> |