Question

I am using Varnish 3.0.3 and to use it to leverage browser caching by setting a maximum age in the HTTP headers for static resources. I tried adding the following configuration to default.vcl:

sub vcl_fetch {
  if (beresp.cacheable) {
    /* Remove Expires from backend, it's not long enough */
    unset beresp.http.expires;

    /* Set the clients TTL on this object */
    set beresp.http.cache-control = "max-age=900";

    /* Set how long Varnish will keep it */
    set beresp.ttl = 1w;

    /* marker for vcl_deliver to reset Age: */
    set beresp.http.magicmarker = "1";
  }
}

sub vcl_deliver {
  if (resp.http.magicmarker) {
    /* Remove the magic marker */
    unset resp.http.magicmarker;

    /* By definition we have a fresh object */
    set resp.http.age = "0";
  }
}

This is copied from https://www.varnish-cache.org/trac/wiki/VCLExampleLongerCaching . Maybe I just made a typo. On restart of Varnish, it no longer worked.

I have two questions. Is this the correct way to do it for Varnish 3? If so, what am I doing wrong? Secondly, is there a way to test the Varnish configuration file, before a restart? Something along the ways of what Apache has with “/sbin/service httpd configtest”. That catches mistakes before going live. Thank you.

Answer 1

Yes, in general this is the way of overriding the backend’s TTL.
Remove beresp.http.expires, set beresp.http.cache-control, set beresp.ttl.
beresp.cacheable is a 2.[01]-ism. The same test in 3.0 is to check that beresp.ttl > 0.

A small tip is to store your magic marker on req.http instead, then you don’t have to clean it up before handing the object to the client.

With regards to testing a configuration file, you can call the VCL compiler directly with “varnishd -C -f /etc/varnish/default.vcl” for example. If your VCL is faulty you get the error message, if the VCL is valid you get a few pages with generated C code.