Provided by: varnish_1.1.2_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.

     The contents of another VCL file may be inserted at any point in the code
     by using the include keyword followed by the name of the other file as a
     quoted string.

   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;
         }

   Functions
     The following built-in functions are available:

     regsub(str, regex, sub)
             Returns a copy of str with all occurrences of the regular
             expression regex replaced with sub.  Within sub, $0 (which can
             also be spelled &) is replaced with the entire matched string,
             and $n is replaced with the contents of subgroup n in the matched
             string.

     purge_url(regex)
             Purge all objects in cache whose URLs match regex.

   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.

     If multiple subroutines with the same name are defined, they are
     concatenated in the order in which the appear in the source.

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

         call pipe_if_local;

     There are a number of special subroutines which hook into the Varnish
     workflow.  These subroutines may inspect and manipulate HTTP headers and
     various other aspects of each request, and to a certain extent decide how
     the request should be handled.  Each subroutine terminates by calling one
     of a small number of keywords which indicates the desired outcome.

     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 applicable,
             which backend to use.

             The vcl_recv subroutine may terminate with one of the following
             keywords:

             error code [reason]
                     Return the specified error code to the client and abandon
                     the request.

             pass    Switch to pass mode.  Control will eventually pass to
                     vcl_pass.

             pipe    Switch to pipe mode.  Control will eventually pass to
                     vcl_pipe.

             lookup  Look up the requested object in the cache.  Control will
                     eventually pass to vcl_hit or vcl_miss, depending on
                     whether the object is in the cache.

     vcl_pipe
             Called upon entering pipe mode.  In this mode, the request is
             passed on to the backend, and any further data from either client
             or backend is passed on unaltered until either end closes the
             connection.

             The vcl_pipe subroutine may terminate with one of the following
             keywords:

             error code [reason]
                     Return the specified error code to the client and abandon
                     the request.

             pipe    Proceed with pipe mode.

     vcl_pass
             Called upon entering pass mode.  In this mode, the request is
             passed on to the backend, and the backend’s response is passed on
             to the client, but is not entered into the cache.  Subsequent
             requests submitted over the same client connection are handled
             normally.

             The vcl_pass subroutine may terminate with one of the following
             keywords:

             error code [reason]
                     Return the specified error code to the client and abandon
                     the request.

             pass    Proceed with pass mode.

     vcl_hash
             Currently not used.  The vcl_hash subroutine may terminate with
             one of the following keywords:

             hash    Proceed.

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

             The vcl_hit subroutine may terminate with one of the following
             keywords:

             error code [reason]
                     Return the specified error code to the client and abandon
                     the request.

             pass    Switch to pass mode.  Control will eventually pass to
                     vcl_pass.

             deliver
                     Deliver the cached object to the client.  Control will
                     eventually pass to vcl_deliver.

     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.

             The vcl_miss subroutine may terminate with one of the following
             keywords:

             error code [reason]
                     Return the specified error code to the client and abandon
                     the request.

             pass    Switch to pass mode.  Control will eventually pass to
                     vcl_pass.

             fetch   Retrieve the requested object from the backend.  Control
                     will eventually pass to vcl_fetch.

     vcl_fetch
             Called after a document has been successfully retrieved from the
             backend.

             The vcl_fetch subroutine may terminate with one of the following
             keywords:

             error code [reason]
                     Return the specified error code to the client and abandon
                     the request.

             pass    Switch to pass mode.  Control will eventually pass to
                     vcl_pass.

             insert  Insert the object into the cache, then deliver it to the
                     client.  Control will eventually pass to vcl_deliver.

     vcl_deliver
             Called before a cached object is delivered to the client.

             The vcl_deliver subroutine may terminate with one of the
             following keywords:

             error code [reason]
                     Return the specified error code to the client and abandon
                     the request.

             deliver
                     Deliver the object to the client.

     vcl_timeout
             Called by the reaper thread shortly before a cached document
             reaches its expiry time.

             The vcl_timeout subroutine may terminate with one of the
             following keywords:

             fetch   Request a fresh copy of the object from the backend.

             discard
                     Discard the object.

     vcl_discard
             Called by the reaper thread when a cached document is about to be
             discarded, either because it has expired or because space is
             running low.

             The vcl_discard subroutine may terminate with one of the
             following keywords:

             discard
                     Discard the object.

             keep    Keep the object in cache.

     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 always available:

     now   The current time, in seconds since the epoch.

     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.

     server.ip
           The IP address of the socket on which the client connection was
           received.

     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 HTTP header.

     The following variables are available while preparing a backend request
     (either for a cache miss or for pass or pipe mode):

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

     bereq.url
           The requested URL.

     bereq.proto
           The HTTP protocol version used to talk to the server.

     bereq.http.header
           The corresponding HTTP header.

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

     obj.proto
           The HTTP protocol version used when the object was retrieved.

     obj.status
           The HTTP status code returned by the server.

     obj.response
           The HTTP status message returned by the server.

     obj.valid
           True if the request resulted in a valid HTTP response.

     obj.cacheable
           True if the request resulted in a cacheable response.  A response
           is considered cacheable if it is valid (see above), the HTTP status
           code is 200, 203, 300, 301, 302, 404 or 410 and it has a non-zero
           time-to-live when Expires and Cache-Control headers are taken into
           account.

     obj.ttl
           The object’s remaining time to live, in seconds.

     obj.lastuse
           The approximate time elapsed since the object was last requests, in
           seconds.

     The following variables are available while preparing a response to the
     client:

     resp.proto
           The HTTP protocol version to use for the response.

     resp.status
           The HTTP status code that will be returned.

     resp.response
           The HTTP status message that will be returned.

     resp.http.header
           The corresponding HTTP header.

     Values may be assigned to variables using the set keyword:

         sub vcl_recv {
             # Normalize the Host: header
             if (req.http.host ~ "^(www.)?example.com$") {
                 set req.http.host = "www.example.com";
             }
         }

     HTTP headers can be removed entirely using the remove keyword:

         sub vcl_fetch {
             # Don’t cache cookies
             remove obj.http.Set-Cookie;
         }

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_pipe {
             pipe;
         }

         sub vcl_pass {
             pass;
         }

         sub vcl_hash {
             set req.hash += req.url;
             set req.hash += req.http.host;
             hash;
         }

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

         sub vcl_miss {
             fetch;
         }

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

         sub vcl_deliver {
             deliver;
         }

         sub vcl_timeout {
             discard;
         }

         sub vcl_discard {
             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$") {
                 set req.http.host = "www.example.com";
                 set req.backend = www;
             } elsif (req.http.host ~ "^images.example.com$") {
                 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 (obj.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〉.