Commit df41130c authored by Per Andreas Buer's avatar Per Andreas Buer

VCL Basics

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@4856 d4fa192b-c00b-0410-8231-f00ffab90ce4
parent 75b40a64
...@@ -31,7 +31,12 @@ subroutines of the configuration at the relevant times. ...@@ -31,7 +31,12 @@ subroutines of the configuration at the relevant times.
Varnish will execute these subroutines of code at different stages of Varnish will execute these subroutines of code at different stages of
its work. Since its code it's execute line by line and precedence its work. Since its code it's execute line by line and precedence
isn't a problem. isn't a problem. At some point you call an action in this subroutine
and then the execution of the subroutine stops.
If you don't call an action in your subroutine and it reaches the end
Varnish will execute some built in code as well. We discuss this in
XXX: Appendix A - the builtin VCL.
99% of all the changes you'll need to do will be done in two of these 99% of all the changes you'll need to do will be done in two of these
subroutines. subroutines.
...@@ -47,7 +52,6 @@ the request, how to do it, and, if applicable, which backend to use. ...@@ -47,7 +52,6 @@ the request, how to do it, and, if applicable, which backend to use.
In vcl_recv you can also alter the request, dropping cookies, rewrite In vcl_recv you can also alter the request, dropping cookies, rewrite
headers. headers.
vcl_fetch vcl_fetch
~~~~~~~~~ ~~~~~~~~~
...@@ -56,6 +60,69 @@ from the backend. Normal tasks her are to alter the response headers, ...@@ -56,6 +60,69 @@ from the backend. Normal tasks her are to alter the response headers,
trigger ESI processing, try alternate backend servers in case the trigger ESI processing, try alternate backend servers in case the
request failed. request failed.
actions
~~~~~~~
The most common actions to call are these:
*pass*
When you call pass the request and subsequent response will be passed
to and from the backend server. It won't be cached. pass can be called
in both vcl_recv and vcl_fetch.
*lookup*
When you call lookup from vcl_recv you tell Varnish to deliver content
from cache even if the request othervise indicates that the request
should be passed. You can't call lookup from vcl_fetch.
*pipe*
*deliver*
*esi*
ESI-process the fetched document.
Example 1 - manipulating headers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Lets say we want to remove the cookie for all objects in the /static
directory of our web server:::
sub vcl_recv {
if (req.url ~ "^/images") {
unset req.http.cookie;
}
}
Now, when the request is handled to the backend server there will be
no cookie header. The interesting line is the one with the
if-statement. It probably needs a bit of explaining. Varnish has a few
objects that are available throughout the VCL. The important ones are:
*req*
The request object. Each HTTP transaction contains a request and a
response. When Varnish has recieved the request the req object is
created and populated. Most of the work you do in vcl_fetch you
do on or with the req object.
*beresp*
The backend respons object. It contains the headers of the object
comming from the backend. Most of the work you do in vcl_fetch you
do on the beresp object.
Example 2 - manipulating beresp
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here we override the TTL of a object comming from the backend if it
matches certain criteria:::
sub vcl_fetch {
if (beresp.url ~ "\.(png|gif|jpg)$") {
unset beresp.http.set-cookie;
beresp.ttl = 3600;
}
}
Example one Example 3 - ACLs
~~~~~~~~~~~ ~~~~~~~~~~~~~~~~
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