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<div class="section" id="varnish-configuration-language-vcl"> |
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<h1>Varnish Configuration Language - VCL<a class="headerlink" href="#varnish-configuration-language-vcl" title="Permalink to this headline">¶</a></h1> |
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<p>Varnish has a great configuration system. Most other systems use |
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configuration directives, where you basically turn on and off lots of |
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switches. Varnish uses a domain specific language called Varnish |
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Configuration Language, or VCL for short. Varnish translates this |
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configuration into binary code which is then executed when requests |
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arrive.</p> |
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<p>The VCL files are divided into subroutines. The different subroutines |
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are executed at different times. One is executed when we get the |
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request, another when files are fetched from the backend server.</p> |
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<p>Varnish will execute these subroutines of code at different stages of |
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its work. Because it is code it is execute line by line precedence |
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isn't a problem. At some point you call an action in this subroutine |
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and then the execution of the subroutine stops.</p> |
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<p>If you don't call an action in your subroutine and it reaches the end |
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Varnish will execute some built in VCL code. You will see this VCL |
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code commented out in default.vcl.</p> |
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<p>99% of all the changes you'll need to do will be done in two of these |
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subroutines. <em>vcl_recv</em> and <em>vcl_fetch</em>.</p> |
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<div class="section" id="vcl-recv"> |
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<h2>vcl_recv<a class="headerlink" href="#vcl-recv" title="Permalink to this headline">¶</a></h2> |
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<p>vcl_recv (yes, we're skimpy with characters, it's Unix) is called at |
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the beginning of a request, after the complete request has been |
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received and parsed. Its purpose is to decide whether or not to serve |
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the request, how to do it, and, if applicable, which backend to use.</p> |
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<p>In vcl_recv you can also alter the request. Typically you can alter |
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the cookies and add and remove request headers.</p> |
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<p>Note that in vcl_recv only the request object, req is available.</p> |
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</div> |
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<div class="section" id="vcl-fetch"> |
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<h2>vcl_fetch<a class="headerlink" href="#vcl-fetch" title="Permalink to this headline">¶</a></h2> |
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<p>vcl_fetch is called <em>after</em> a document has been successfully retrieved |
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from the backend. Normal tasks her are to alter the response headers, |
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trigger ESI processing, try alternate backend servers in case the |
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request failed.</p> |
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<p>In vcl_fetch you still have the request object, req, available. There |
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is also a <em>backend response</em>, beresp. beresp will contain the HTTP |
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headers from the backend.</p> |
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</div> |
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<div class="section" id="actions"> |
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<h2>actions<a class="headerlink" href="#actions" title="Permalink to this headline">¶</a></h2> |
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<p>The most common actions to return are these:</p> |
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<dl class="docutils"> |
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<dt><em>pass</em></dt> |
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<dd>When you return pass the request and subsequent response will be passed to |
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and from the backend server. It won't be cached. pass can be returned from |
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vcl_recv</dd> |
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<dt><em>hit_for_pass</em></dt> |
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<dd>Similar to pass, but accessible from vcl_fetch. Unlike pass, hit_for_pass |
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will create a hitforpass object in the cache. This has the side-effect of |
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caching the decision not to cache. This is to allow would-be uncachable |
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requests to be passed to the backend at the same time. The same logic is |
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not necessary in vcl_recv because this happens before any potential |
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queueing for an object takes place.</dd> |
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<dt><em>lookup</em></dt> |
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<dd>When you return lookup from vcl_recv you tell Varnish to deliver content |
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from cache even if the request othervise indicates that the request |
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should be passed. You can't return lookup from vcl_fetch.</dd> |
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<dt><em>pipe</em></dt> |
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<dd>Pipe can be returned from vcl_recv as well. Pipe short circuits the |
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client and the backend connections and Varnish will just sit there |
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and shuffle bytes back and forth. Varnish will not look at the data being |
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send back and forth - so your logs will be incomplete. |
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Beware that with HTTP 1.1 a client can send several requests on the same |
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connection and so you should instruct Varnish to add a "Connection: close" |
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header before actually returning pipe.</dd> |
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<dt><em>deliver</em></dt> |
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<dd>Deliver the cached object to the client. Usually returned from vcl_fetch.</dd> |
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</dl> |
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</div> |
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<div class="section" id="requests-responses-and-objects"> |
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<h2>Requests, responses and objects<a class="headerlink" href="#requests-responses-and-objects" title="Permalink to this headline">¶</a></h2> |
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<p>In VCL, there are three important data structures. The request, coming |
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from the client, the response coming from the backend server and the |
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object, stored in cache.</p> |
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<p>In VCL you should know the following structures.</p> |
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<dl class="docutils"> |
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<dt><em>req</em></dt> |
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<dd>The request object. When Varnish has received the request the req object is |
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created and populated. Most of the work you do in vcl_recv you |
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do on or with the req object.</dd> |
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<dt><em>beresp</em></dt> |
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<dd>The backend respons object. It contains the headers of the object |
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comming from the backend. Most of the work you do in vcl_fetch you |
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do on the beresp object.</dd> |
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<dt><em>obj</em></dt> |
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<dd>The cached object. Mostly a read only object that resides in memory. |
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obj.ttl is writable, the rest is read only.</dd> |
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</dl> |
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</div> |
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<div class="section" id="operators"> |
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<h2>Operators<a class="headerlink" href="#operators" title="Permalink to this headline">¶</a></h2> |
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<p>The following operators are available in VCL. See the examples further |
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down for, uhm, examples.</p> |
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<dl class="docutils"> |
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<dt>=</dt> |
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<dd>Assignment operator.</dd> |
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</dl> |
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<dl class="docutils"> |
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<dt>==</dt> |
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<dd>Comparison.</dd> |
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</dl> |
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<dl class="docutils"> |
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<dt>~</dt> |
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<dd>Match. Can either be used with regular expressions or ACLs.</dd> |
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</dl> |
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<dl class="docutils"> |
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<dt>!</dt> |
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<dd>Negation.</dd> |
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</dl> |
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<dl class="docutils"> |
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<dt>&&</dt> |
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<dd>Logical <em>and</em></dd> |
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</dl> |
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<dl class="docutils"> |
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<dt>||</dt> |
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<dd>Logical <em>or</em></dd> |
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</dl> |
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</div> |
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<div class="section" id="example-1-manipulating-headers"> |
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<h2>Example 1 - manipulating headers<a class="headerlink" href="#example-1-manipulating-headers" title="Permalink to this headline">¶</a></h2> |
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<p>Lets say we want to remove the cookie for all objects in the /images |
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directory of our web server:</p> |
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<div class="highlight-python"><pre>sub vcl_recv { |
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if (req.url ~ "^/images") {
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unset req.http.cookie; |
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} |
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}</pre> |
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</div> |
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<p>Now, when the request is handled to the backend server there will be |
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no cookie header. The interesting line is the one with the |
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if-statement. It matches the URL, taken from the request object, and |
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matches it against the regular expression. Note the match operator. If |
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it matches the Cookie: header of the request is unset (deleted).</p> |
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</div> |
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<div class="section" id="example-2-manipulating-beresp"> |
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<h2>Example 2 - manipulating beresp<a class="headerlink" href="#example-2-manipulating-beresp" title="Permalink to this headline">¶</a></h2> |
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<p>Here we override the TTL of a object comming from the backend if it |
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matches certain criteria:</p> |
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<div class="highlight-python"><pre>sub vcl_fetch { |
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if (req.url ~ "\.(png|gif|jpg)$") {
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unset beresp.http.set-cookie; |
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set beresp.ttl = 1h; |
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} |
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}</pre> |
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</div> |
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</div> |
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<div class="section" id="example-3-acls"> |
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<h2>Example 3 - ACLs<a class="headerlink" href="#example-3-acls" title="Permalink to this headline">¶</a></h2> |
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<p>You create a named access control list with the <em>acl</em> keyword. You can match |
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the IP address of the client against an ACL with the match operator.:</p> |
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<div class="highlight-python"><pre># Who is allowed to purge.... |
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acl local {
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"localhost"; |
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"192.168.1.0"/24; /* and everyone on the local network */ |
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! "192.168.1.23"; /* except for the dialin router */ |
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} |
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sub vcl_recv {
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if (req.request == "PURGE") {
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if (client.ip ~ local) {
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return(lookup); |
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} |
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} |
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} |
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sub vcl_hit {
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if (req.request == "PURGE") {
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set obj.ttl = 0s; |
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error 200 "Purged."; |
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} |
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} |
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sub vcl_miss {
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if (req.request == "PURGE") {
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error 404 "Not in cache."; |
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} |
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}</pre> |
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</div> |
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</div> |
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</div> |
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</div> |
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<div class="sphinxsidebar"> |
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<div class="sphinxsidebarwrapper"> |
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<h3><a href="../index.html">Table Of Contents</a></h3> |
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<ul> |
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<li><a class="reference internal" href="#">Varnish Configuration Language - VCL</a><ul> |
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<li><a class="reference internal" href="#vcl-recv">vcl_recv</a></li> |
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<li><a class="reference internal" href="#vcl-fetch">vcl_fetch</a></li> |
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<li><a class="reference internal" href="#actions">actions</a></li> |
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<li><a class="reference internal" href="#requests-responses-and-objects">Requests, responses and objects</a></li> |
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<li><a class="reference internal" href="#operators">Operators</a></li> |
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<li><a class="reference internal" href="#example-1-manipulating-headers">Example 1 - manipulating headers</a></li> |
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<li><a class="reference internal" href="#example-2-manipulating-beresp">Example 2 - manipulating beresp</a></li> |
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<li><a class="reference internal" href="#example-3-acls">Example 3 - ACLs</a></li> |
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</ul> |
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</li> |
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</ul> |
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<p class="topless"><a href="putting_varnish_on_port_80.html" |
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title="previous chapter">Put Varnish on port 80</a></p> |
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<h4>Next topic</h4> |
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<p class="topless"><a href="statistics.html" |
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title="next chapter">Statistics</a></p> |
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