Varnish Cache - default TTL?

Question

I have discovered that I can set the TTL in Varnish as follows in my VCL file:

sub vcl_fetch {
    # 1 minute
    set obj.ttl = 1m;
}

But what is the default setting (assuming the backend server is setting no cache-control header) ?

Answer 1

This is in the default template:

sub vcl_fetch {
    if (beresp.ttl <= 0s ||
        beresp.http.Set-Cookie ||
        beresp.http.Vary == "*") {
                /*
                 * Mark as "Hit-For-Pass" for the next 2 minutes
                 */
                set beresp.ttl = 120 s;
                return (hit_for_pass);
    }
    return (deliver);
}

So, 120 seconds.

Answer 2

Default TTL can be passed through the varnishd command via the -t commandline switch and is probably sourced from a properties file on your filesystem. On the CentOS system I'm looking at it is set using DEFAULT_TTL from /etc/sysconfig/varnish.

You can see the live setting using varnishadm like so,

varnishadm param.show default_ttl

Actually, following default VCL logic relates to non-cacheable objects.

  sub vcl_fetch {
      if (beresp.ttl <= 0s ||
          beresp.http.Set-Cookie ||
          beresp.http.Vary == "*") {
                  /*
                   * Mark as "Hit-For-Pass" for the next 2 minutes
                   */
                  set beresp.ttl = 120 s;
                  return (hit_for_pass);
      }
      return (deliver);
  }

means "if object is not cacheable - pass client requests for this object to backend directly and simultaneously for 2 minutes, do not queue them"

Read more at https://stackoverflow.com/questions/12691489/varnish-hit-for-pass-means