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<?xml version="1.0" encoding="ISO-8859-1"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!-- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX This file is generated from xml source: DO NOT EDIT XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX --><title>mod_proxy_balancer - Apache HTTP Server</title><link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /><link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /><link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link href="../images/favicon.ico" rel="shortcut icon" /></head><body><div id="page-header"><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><p class="apache">Apache HTTP Server Version 2.2</p><img alt="" src="../images/feather.gif" /></div><div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div><div id="path"><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 2.2</a> > <a href="./">Modules</a></div><div id="page-content"><div id="preamble"><h1>Apache Module mod_proxy_balancer</h1><div class="toplang"><p><span>Available Languages: </span><a href="../en/mod/mod_proxy_balancer.html" title="English"> en </a> |<a href="../ja/mod/mod_proxy_balancer.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a></p></div><table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> extension for load balancing </td></tr><tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr><tr><th><a href="module-dict.html#ModuleIdentifier">Module營dentifier:</a></th><td>proxy_balancer_module</td></tr><tr><th><a href="module-dict.html#SourceFile">Source燜ile:</a></th><td>mod_proxy_balancer.c</td></tr><tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td>Available in version 2.1 and later</td></tr></table><h3>Summary</h3> <p>This module <em>requires</em> the service of <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code>. It provides load balancing support for <code>HTTP</code>, <code>FTP</code> and <code>AJP13</code> protocols </p> <p>Thus, in order to get the ability of load balancing, <code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code> and <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> have to be present in the server.</p> <div class="warning"><h3>Warning</h3> <p>Do not enable proxying until you have <a href="mod_proxy.html#access">secured your server</a>. Open proxy servers are dangerous both to your network and to the Internet at large.</p> </div></div><div id="quickview"><h3 class="directives">Directives</h3><p>This module provides no directives.</p><h3>Topics</h3><ul id="topics"><li><img alt="" src="../images/down.gif" /> <a href="#scheduler">Load balancer scheduler algorithm</a></li><li><img alt="" src="../images/down.gif" /> <a href="#example">Example of a balancer configuration</a></li><li><img alt="" src="../images/down.gif" /> <a href="#requests">Request Counting Algorithm</a></li><li><img alt="" src="../images/down.gif" /> <a href="#traffic">Weighted Traffic Counting Algorithm</a></li><li><img alt="" src="../images/down.gif" /> <a href="#busyness">Pending Request Counting Algorithm</a></li><li><img alt="" src="../images/down.gif" /> <a href="#environment">Exported Environment Variables</a></li><li><img alt="" src="../images/down.gif" /> <a href="#enable">Enabling Balancer Manager Support</a></li></ul><h3>See also</h3><ul class="seealso"><li><code class="module"><a href="../mod/mod_proxy.html">mod_proxy</a></code></li></ul></div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="section"><h2><a name="scheduler" id="scheduler">Load balancer scheduler algorithm</a></h2> <p>At present, there are 3 load balancer scheduler algorithms available for use: Request Counting, Weighted Traffic Counting and Pending Request Counting. These are controlled via the <code>lbmethod</code> value of the Balancer definition. See the <code class="directive"><a href="../mod/mod_proxy.html#proxypass">ProxyPass</a></code> directive for more information.</p></div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="section"><h2><a name="example" id="example">Example of a balancer configuration</a></h2> <p>Before we dive into the technical details, here's an example of how you might use <code class="module"><a href="../mod/mod_proxy_balancer.html">mod_proxy_balancer</a></code> to provide load balancing between two back-end servers: </p> <div class="example"><p><code> <Proxy balancer://mycluster><br /> BalancerMember http://192.168.1.50:80<br /> BalancerMember http://192.168.1.51:80<br /> </Proxy><br /> ProxyPass /test balancer://mycluster/ </code></p></div></div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div><div class="section"><h2><a name="requests" id="requests">Request Counting Algorithm</a></h2> <p>Enabled via <code>lbmethod=byrequests</code>, the idea behind this scheduler is that we distribute the requests among the various workers to ensure that each gets their configured share of the number of requests. It works as follows:</p> <p><dfn>lbfactor</dfn> is <em>how much we expect this worker to work</em>, or <em>the workers's work quota</em>. This is a normalized value representing their "share" of the amount of work to be done.</p> <p><dfn>lbstatus</dfn> is <em>how urgent this worker has to work to fulfill its quota of work</em>.</p> <p>The <dfn>worker</dfn> is a member of the load balancer, usually a remote host serving one of the supported protocols.</p> <p>We distribute each worker's work quota to the worker, and then look which of them needs to work most urgently (biggest lbstatus). This worker is then selected for work, and its lbstatus reduced by the total work quota we distributed to all workers. Thus the sum of all lbstatus does not change(*) and we distribute the requests as desired.</p> <p>If some workers are disabled, the others will still be scheduled correctly.</p> <div class="example"><pre><code>for each worker in workers worker lbstatus += worker lbfactor total factor += worker lbfactor if worker lbstatus > candidate lbstatus candidate = workercandidate lbstatus -= total factor</code></pre></div> <p>If a balancer is configured as follows:</p> <table><tr><th>worker</th> <th class="data">a</th> <th class="data">b</th> <th class="data">c</th> <th class="data">d</th></tr><tr><th>lbfactor</th> <td class="data">25</td> <td class="data">25</td> <td class="data">25</td> <td class="data">25</td></tr><tr><th>lbstatus</th> <td class="data">0</td> <td class="data">0</td> <td class="data">0</td> <td class="data">0</td></tr></table> <p>And <var>b</var> gets disabled, the following schedule is produced:</p> <table><tr><th>worker</th> <th class="data">a</th> <th class="data">b</th> <th class="data">c</th> <th class="data">d</th></tr><tr><th>lbstatus</th> <td class="data"><em>-50</em></td> <td class="data">0</td> <td class="data">25</td> <td class="data">25</td></tr><tr><th>lbstatus</th> <td class="data">-25</td> <td class="data">0</td> <td class="data"><em>-25</em></td> <td class="data">50</td></tr><tr><th>lbstatus</th> <td class="data">0</td> <td class="data">0</td> <td class="data">0</td> <td class="data"><em>0</em></td></tr><tr><td class="data" colspan="5">(repeat)</td></tr></table> <p>That is it schedules: <var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var> <var>d</var> <var>a</var> <var>c</var> <var>d</var> ... Please note that:</p> <table><tr><th>worker</th> <th class="data">a</th> <th class="data">b</th> <th class="data">c</th> <th class="data">d</th></tr><tr><th>lbfactor</th> <td class="data">25</td> <td class="data">25</td> <td class="data">25</td> <td class="data">25</td></tr></table> <p>Has the exact same behavior as:</p> <table><tr><th>worker</th> <th class="data">a</th> <th class="data">b</th> <th class="data">c</th> <th class="data">d</th></tr><tr><th>lbfactor</th> <td class="data">1</td> <td class="data">1</td> <td class="data">1</td> <td class="data">1</td></tr></table> <p>This is because all values of <dfn>lbfactor</dfn> are normalized with respect to the others. For:</p>⌨️ 快捷键说明
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