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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <title>Hashing — Varnish version 5.2.1 documentation</title> <link rel="stylesheet" href="../_static/classic.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript"> var DOCUMENTATION_OPTIONS = { URL_ROOT: '../', VERSION: '5.2.1', COLLAPSE_INDEX: false, FILE_SUFFIX: '.html', HAS_SOURCE: true }; </script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="top" title="Varnish version 5.2.1 documentation" href="../index.html" /> <link rel="up" title="VCL - Varnish Configuration Language" href="vcl.html" /> <link rel="next" title="Misbehaving servers" href="vcl-grace.html" /> <link rel="prev" title="Backend servers" href="vcl-backends.html" /> </head> <body role="document"> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="vcl-grace.html" title="Misbehaving servers" accesskey="N">next</a> |</li> <li class="right" > <a href="vcl-backends.html" title="Backend servers" accesskey="P">previous</a> |</li> <li class="nav-item nav-item-0"><a href="../index.html">Varnish version 5.2.1 documentation</a> »</li> <li class="nav-item nav-item-1"><a href="index.html" >The Varnish Users Guide</a> »</li> <li class="nav-item nav-item-2"><a href="vcl.html" accesskey="U">VCL - Varnish Configuration Language</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="hashing"> <h1>Hashing<a class="headerlink" href="#hashing" title="Permalink to this headline">ΒΆ</a></h1> <p>Internally, when Varnish stores content in the cache it stores the object together with a hash key to find the object again. In the default setup this key is calculated based on the content of the <em>Host</em> header or the IP address of the server and the URL.</p> <p>Behold the <cite>default vcl</cite>:</p> <div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">sub</span> <span class="n">vcl_hash</span> <span class="p">{</span> <span class="n">hash_data</span><span class="p">(</span><span class="n">req</span><span class="o">.</span><span class="n">url</span><span class="p">);</span> <span class="k">if</span> <span class="p">(</span><span class="n">req</span><span class="o">.</span><span class="n">http</span><span class="o">.</span><span class="n">host</span><span class="p">)</span> <span class="p">{</span> <span class="n">hash_data</span><span class="p">(</span><span class="n">req</span><span class="o">.</span><span class="n">http</span><span class="o">.</span><span class="n">host</span><span class="p">);</span> <span class="p">}</span> <span class="k">else</span> <span class="p">{</span> <span class="n">hash_data</span><span class="p">(</span><span class="n">server</span><span class="o">.</span><span class="n">ip</span><span class="p">);</span> <span class="p">}</span> <span class="k">return</span> <span class="p">(</span><span class="n">lookup</span><span class="p">);</span> <span class="p">}</span> </pre></div> </div> <p>As you can see it first checks in <cite>req.url</cite> then <cite>req.http.host</cite> if it exists. It is worth pointing out that Varnish doesn't lowercase the hostname or the URL before hashing it so in theory having "Varnish.org/" and "varnish.org/" would result in different cache entries. Browsers however, tend to lowercase hostnames.</p> <p>You can change what goes into the hash. This way you can make Varnish serve up different content to different clients based on arbitrary criteria.</p> <p>Let's say you want to serve pages in different languages to your users based on where their IP address is located. You would need some Vmod to get a country code and then put it into the hash. It might look like this.</p> <p>In <cite>vcl_recv</cite>:</p> <div class="highlight-default"><div class="highlight"><pre><span></span><span class="nb">set</span> <span class="n">req</span><span class="o">.</span><span class="n">http</span><span class="o">.</span><span class="n">X</span><span class="o">-</span><span class="n">Country</span><span class="o">-</span><span class="n">Code</span> <span class="o">=</span> <span class="n">geoip</span><span class="o">.</span><span class="n">lookup</span><span class="p">(</span><span class="n">client</span><span class="o">.</span><span class="n">ip</span><span class="p">);</span> </pre></div> </div> <p>And then add a <cite>vcl_hash</cite>:</p> <div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">sub</span> <span class="n">vcl_hash</span> <span class="p">{</span> <span class="n">hash_data</span><span class="p">(</span><span class="n">req</span><span class="o">.</span><span class="n">http</span><span class="o">.</span><span class="n">X</span><span class="o">-</span><span class="n">Country</span><span class="o">-</span><span class="n">Code</span><span class="p">);</span> <span class="p">}</span> </pre></div> </div> <p>As the default VCL will take care of adding the host and URL to the hash we don't have to do anything else. Be careful calling <code class="docutils literal"><span class="pre">return</span> <span class="pre">(lookup)</span></code> as this will abort the execution of the default VCL and Varnish can end up returning data based on more or less random inputs.</p> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h4>Previous topic</h4> <p class="topless"><a href="vcl-backends.html" title="previous chapter">Backend servers</a></p> <h4>Next topic</h4> <p class="topless"><a href="vcl-grace.html" title="next chapter">Misbehaving servers</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../_sources/users-guide/vcl-hashing.txt" rel="nofollow">Show Source</a></li> </ul> </div> <div id="searchbox" style="display: none" role="search"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <div><input type="text" name="q" /></div> <div><input type="submit" value="Go" /></div> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="vcl-grace.html" title="Misbehaving servers" >next</a> |</li> <li class="right" > <a href="vcl-backends.html" title="Backend servers" >previous</a> |</li> <li class="nav-item nav-item-0"><a href="../index.html">Varnish version 5.2.1 documentation</a> »</li> <li class="nav-item nav-item-1"><a href="index.html" >The Varnish Users Guide</a> »</li> <li class="nav-item nav-item-2"><a href="vcl.html" >VCL - Varnish Configuration Language</a> »</li> </ul> </div> <div class="footer" role="contentinfo"> © Copyright 2010-2014, Varnish Software AS. 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