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 141 <h1 id="head-46349e4051ab58f9d43b4e4cbe75a22812583dc1">ngx_http_upstream_hash_module</h1>
 142 <span class="anchor" id="line-3"></span><span class="anchor" id="line-4"></span><p class="line867"><em>This module is not distributed with the Nginx source. Installation instructions are <a href="#installation">below</a>.</em> <span class="anchor" id="line-5"></span><span class="anchor" id="line-6"></span><p class="line874">The upstream_hash module provides simple upstream load distribution by hashing a configurable variable (e.g., the request URI, incoming HTTP headers, or some combination). Example usage: <span class="anchor" id="line-7"></span><span class="anchor" id="line-8"></span><p class="line867"><span class="anchor" id="line-9"></span><pre>upstream backend {
 143 <span class="anchor" id="line-10"></span>    server server1;
 144 <span class="anchor" id="line-11"></span>    server server2;
 145 <span class="anchor" id="line-12"></span>    hash   $request_uri;
 146 <span class="anchor" id="line-13"></span>}
 147 <span class="anchor" id="line-14"></span></pre><span class="anchor" id="line-15"></span><span class="anchor" id="line-16"></span><p class="line874">Here, Nginx will choose server1 or server2 by hashing the request URI ($request_uri). <span class="anchor" id="line-17"></span><span class="anchor" id="line-18"></span><p class="line867">
 148 <h2 id="head-e447c504fe73e1912886e3cfd5b335eb8a90a5a0">Directives</h2>
 149 <span class="anchor" id="line-19"></span><span class="anchor" id="line-20"></span><ul><li><p class="line891"><a href="#hash">hash</a> <span class="anchor" id="line-21"></span></li><li><p class="line891"><a href="#hash_again">hash_again</a> <span class="anchor" id="line-22"></span><span class="anchor" id="line-23"></span></li></ul><p class="line867"><span class="anchor" id="hash"></span> <span class="anchor" id="line-24"></span><span class="anchor" id="line-25"></span><p class="line867">
 150 <h2 id="head-3a857993d71a23ea824e238814ca4583265bc97d">hash</h2>
 151 <span class="anchor" id="line-26"></span><p class="line867"><strong>syntax</strong> <em>hash $variable</em> <span class="anchor" id="line-27"></span><span class="anchor" id="line-28"></span><p class="line867"><strong>context</strong> <em>upstream</em> <span class="anchor" id="line-29"></span><span class="anchor" id="line-30"></span><p class="line874">Enables upstream hashing of $variable. <span class="anchor" id="line-31"></span><span class="anchor" id="line-32"></span><p class="line874">When present, the "server" directives cannot take any arguments ("weight", "max_fails", etc.). <span class="anchor" id="line-33"></span><span class="anchor" id="line-34"></span><p class="line867"><span class="anchor" id="hash_again"></span> <span class="anchor" id="line-35"></span>
 152 <h2 id="head-36e090dc2c1cb75051fdd971bed7a8c6e8ce3cac">hash_again</h2>
 153 <span class="anchor" id="line-36"></span><p class="line867"><strong>syntax</strong> <em>hash_again number</em> <span class="anchor" id="line-37"></span><span class="anchor" id="line-38"></span><p class="line867"><strong>default</strong> <em>0</em> <span class="anchor" id="line-39"></span><span class="anchor" id="line-40"></span><p class="line867"><strong>context</strong> <em>upstream</em> <span class="anchor" id="line-41"></span><span class="anchor" id="line-42"></span><p class="line874">Number of times to rehash the value and choose a different server if the backend connection fails. Increase this number to provide high availability. <span class="anchor" id="line-43"></span><span class="anchor" id="line-44"></span><p class="line867"><span class="anchor" id="installation"></span> <span class="anchor" id="line-45"></span>
 154 <h2 id="head-f853b6cf504ff6af886bbf45b2dc09a3031f03d9">Installation</h2>
 155 <span class="anchor" id="line-46"></span><span class="anchor" id="line-47"></span><p class="line862">This module is not distributed with the Nginx source. You can download the request_hash module here: <a class="http" href="http://wiki.codemongers.com/NginxHttpUpstreamRequestHashModule?action=AttachFile&amp;do=get&amp;target=nginx_upstream_hash-0.3.tar.gz">nginx_upstream_hash-0.3.tar.gz</a> <span class="anchor" id="line-48"></span><span class="anchor" id="line-49"></span><p class="line874">After extracting, you will need to patch the latest Nginx source (0.7.11 as of this writing). Run patch like this: <span class="anchor" id="line-50"></span><span class="anchor" id="line-51"></span><p class="line867"><span class="anchor" id="line-52"></span><pre>    cd nginx-0.7.11
 156 <span class="anchor" id="line-53"></span>    patch -p0 &lt; /path/to/upstream/hash/directory/nginx.patch
 157 <span class="anchor" id="line-54"></span></pre><span class="anchor" id="line-55"></span><span class="anchor" id="line-56"></span><p class="line874">Then add the following option to your Nginx ./configure command: <span class="anchor" id="line-57"></span><span class="anchor" id="line-58"></span><p class="line867"><span class="anchor" id="line-59"></span><pre>    --add-module=path/to/upstream/hash/directory
 158 <span class="anchor" id="line-60"></span></pre><span class="anchor" id="line-61"></span><span class="anchor" id="line-62"></span><p class="line874">Then "make" and "make install" as usual. <span class="anchor" id="line-63"></span><span class="anchor" id="line-64"></span><p class="line867"><span class="anchor" id="hash-algorithm"></span> <span class="anchor" id="line-65"></span>
 159 <h2 id="head-3c1201d51559ba07821752cd31e80902ed33cc95">The hash algorithm</h2>
 160 <span class="anchor" id="line-66"></span><span class="anchor" id="line-67"></span><p class="line874">As of 0.3, the hash algorithm and the failover algorithm use a CRC-32 computation compatible with PECL Memcache. <span class="anchor" id="line-68"></span><span class="anchor" id="line-69"></span><p class="line867">
 161 <h2 id="head-1468300db9cf366d94eec4f28e55a85a3d500e58">Changes</h2>
 162 <span class="anchor" id="line-70"></span><span class="anchor" id="line-71"></span><ul><li style="list-style-type:none">* 0.3: Feature: PECL Memcache compatibility. Change: Removed "hash_method" directive. <span class="anchor" id="line-72"></span><span class="anchor" id="line-73"></span></li></ul><p class="line867">
 163 <h2 id="head-5ff00a181108bf241a00b91bf8b7b9344eb005b5">Bugs</h2>
 164 <span class="anchor" id="line-74"></span><span class="anchor" id="line-75"></span><p class="line862">Send bug reports to <a class="http" href="http://emiller.info">Evan Miller</a>. <span class="anchor" id="line-76"></span><span class="anchor" id="bottom"></span></div><div id="pagebottom"></div>
 165 <p id="pageinfo" class="info" lang="en" dir="ltr">NginxHttpUpstreamRequestHashModule  (last edited 2008-08-25 02:18:43 by <span title="Emiller @ 127.0.0.25[127.0.0.25]"><a href="/Emiller" title="Emiller @ 127.0.0.25[127.0.0.25]">Emiller</a></span>)</p>
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