Provided by: varnish_1.0.3-2_i386 bug

NAME

     VCL - Varnish Configuration Language

DESCRIPTION

     The VCL language is a small domain-specific language designed to be used
     to define request handling and document caching policies for the Varnish
     HTTP accelerator.

     When a new configuration is loaded, the varnishd management process
     translates the VCL code to C and compiles it to a shared object which is
     then dynamically linked into the server process.

   Syntax
     The VCL syntax is very simple, and deliberately similar to C and Perl.
     Blocks are delimited by curly braces, statements end with semicolons, and
     comments may be written as in C, C++ or Perl according to your own
     preferences.

     In addition to the C-like assignment (=), comparison (==) and boolean (!,
     && and ||) operators, VCL supports regular expression and ACL matching
     using the ~ operator.

     Unlike C and Perl, the backslash (\) character has no special meaning in
     strings in VCL, so it can be freely used in regular expressions without
     doubling.

     Assignments are introduced with the set keyword.  There are no user-
     defined variables; values can only be assigned to variables attached to
     backend, request or document objects.  Most of these are typed, and the
     values assigned to them must have a compatible unit suffix.

     VCL has if tests, but no loops.

   Backend declarations
     A backend declaration creates and initializes a named backend object:

         backend www {
             set backend.host = "www.example.com";
             set backend.port = "http";
         }

     The backend object can later be used to select a backend at request time:

         if (req.http.host ~ "^(www.)?example.com$") {
             set req.backend = www;
         }

   ACLs
     An ACL declaration creates and initializes a named access control list
     which can later be used to match client addresses:

         acl local {
             "locahost";         /* myself */
             "10.0.0.1"/8;       /* and everyone on the local network */
             ! "10.0.0.23";      /* except for the dialin router */
         }

     If an ACL entry specifies a host name which Varnish is unable to resolve,
     it will match any address it is compared to.  Consequently, if it is
     preceded by a negation mark, it will reject any address it is compared
     to, which may not be what you intended.  If the entry is enclosed in
     parentheses, however, it will simply be ignored.

     To match an IP address against an ACL, simply use the match operator:

         if (client.ip ~ local) {
             pipe;
         }

   Subroutines
     A subroutine is used to group code for legibility or reusability:

         sub pipe_if_local {
             if (client.ip ~ local) {
                 pipe;
             }
         }

     Subroutines in VCL do not take arguments, nor do they return values.

     To call a subroutine, use the call keyword followed by the subroutine’s
     name:

         call pipe_if_local;

     There are five special subroutines which hook into the Varnish workflow:

     vcl_recv     Called at the beginning of a request, after the complete
                  request has been received and parsed.  Its purpose is to
                  decide whether or not to serve the request, how to do it,
                  and, if applicanle, which backend to use.

     vcl_hit      Called after a cache lookup if the requested document was
                  found in the cache.

     vcl_miss     Called after a cache lookup if the requested document was
                  not found in the cache.  Its purpose is to decide whether or
                  not to attempt to retrieve the document from the backend,
                  and which backend to use.

     vcl_fetch    Called after a document has been retrieved from the backend,
                  before it is inserted into the cache.

     vcl_timeout  Called by the reaper thread when a cached document has
                  reached its expiry time.

     If one of these subroutines is left undefined or terminates without
     reaching a handling decision, control will be handed over to the builtin
     default.  See the EXAMPLES section for a listing of the default code.

   Variables
     Although subroutines take no arguments, the necessary information is made
     available to the handler subroutines through global variables.

     The following variables are available in backend declarations:

     backend.host
           Host name or IP address of a backend.

     backend.port
           Service name or port number of a backend.

     The following variables are available while processing a request:

     client.ip
           The client’s IP address.

     req.request
           The request type (e.g. "GET", "HEAD").

     req.url
           The requested URL.

     req.proto
           The HTTP protocol version used by the client.

     req.backend
           The backend to use to service the request.

     req.http.header
           The corresponding header from the HTTP request.

     The following variables are available after the requested object has been
     retrieved from cache or from the backend:

     obj.valid
           True if the object was successfully retrieved.

     obj.cacheable
           True if the object is cacheable.

     obj.ttl
           The object’s time to live.

EXAMPLES

     The following code is the equivalent of the default configuration with
     the backend address set to "backend.example.com" and no backend port
     specified.

         backend default {
             set backend.host = "backend.example.com";
             set backend.port = "http";
         }

         sub vcl_recv {
             if (req.request != "GET" && req.request != "HEAD") {
                 pipe;
             }
             if (req.http.Expect) {
                 pipe;
             }
             if (req.http.Authenticate || req.http.Cookie) {
                 pass;
             }
             lookup;
         }

         sub vcl_hit {
             if (!obj.cacheable) {
                 pass;
             }
             deliver;
         }

         sub vcl_miss {
             fetch;
         }

         sub vcl_fetch {
             if (!obj.valid) {
                 error;
             }
             if (!obj.cacheable) {
                 insert_pass;
             }
             if (resp.http.Set-Cookie) {
                 insert_pass;
             }
             insert;
         }

         sub vcl_timeout {
             discard;
         };

     The following example shows how to support multiple sites running on
     separate backends in the same Varnish instance, by selecting backends
     based on the request URL.

         backend www {
             set backend.host = "www.example.com";
             set backend.port = "80";
         }

         backend images {
             set backend.host = "images.example.com";
             set backend.port = "80";
         }

         sub vcl_recv {
             if (req.http.host ~ "^(www.)?example.com$") {
                 set req.backend = www;
             } elsif (req.http.host ~ "^images.example.com") {
                 set req.backend = images;
             } else {
                 error 404 "Unknown virtual host";
             }
         }

     The following snippet demonstrates how to force a minimum TTL for all
     documents.  Note that this is not the same as setting the default_ttl
     run-time parameter, as that only affects document for which the backend
     did not specify a TTL.

         sub vcl_fetch {
             if (obj.ttl < 120s) {
                 set obj.ttl = 120s;
             }
         }

     The following snippet demonstrates how to force Varnish to cache
     documents even when cookies are present.

         sub vcl_recv {
             if (req.request == "GET" && req.http.cookie) {
                 lookup;
             }
         }

         sub vcl_fetch {
             if (resp.http.Set-Cookie) {
                 insert;
             }
         }

     The following code implements the HTTP PURGE method as used by Squid for
     object invalidation:

         acl purge {
                 "localhost";
                 "10.0.0.1"/8;
         }

         sub vcl_recv {
             if (req.request == "PURGE") {
                 if (!client.ip ~ purge) {
                     error 405 "Not allowed.";
                 }
                 lookup;
             }
         }

         sub vcl_hit {
             if (req.request == "PURGE") {
                 set obj.ttl = 0s;
                 error 200 "Purged.";
             }
         }

         sub vcl_miss {
             if (req.request == "PURGE") {
                 error 404 "Not in cache.";
             }
         }

SEE ALSO

     varnishd(1)

HISTORY

     The VCL language was developed by Poul-Henning Kamp 〈phk@phk.freebsd.dk〉
     in cooperation with Verdens Gang AS and Linpro AS.  This manual page was
     written by Dag-Erling Smørgrav 〈des@linpro.no〉.