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DiverseAndRemote.com
Asked: 2013-05-30 06:07:42 +0800 CST

How do I set a varnish response TTL dynamically?

  • 772

my php script is sending a header X_Cache_ttl: 1h and in my varnish config file I have

sub vcl_fetch
{
    if(beresp.http.X-Cache-ttl){
            set beresp.ttl = beresp.http.X-Cache-ttl;
    }
}

but the line with the set command is causing varnish to fail when I try to start it.

in the log I get 

Expression has type STRING, expected DURATION
('input' Line 116 Pos 34) -- ('input' Line 116 Pos 56)
            set beresp.ttl = beresp.http.X-Cache-ttl;

How do I convert X-Cache-ttl to a duration so that I can dynamically set the TTL?

I would like to avoid multiple if statements similar to 

if(beresp.http.X-Cache-ttl == "60s") {
    set beresp.ttl = 60s;
}

if(beresp.http.X-Cache-ttl == "1h") {
    set beresp.ttl = 1h;
}

If it matters I'm using varnish 3.0.3 on centos 6.

cache

2 Answers

  1. Best Answer

    The vmod_std module has a function that should do what you're looking for.

    import std; at the top of the VCL, then this should work:

    sub vcl_fetch
{
    set beresp.ttl = std.duration(beresp.http.X-Cache-ttl, 1h);
}

    ..where the 1h is your default if the header isn't set.

    • 11

  2. According to the Varnish documentation you can use the Cache-Control header.

    Cache-Control

    The 'Cache-Control' header instructs caches how to handle the content. Varnish cares about the max-age parameter and uses it to calculate the TTL for an object.

    So make sure you issue a 'Cache-Control' header with a max-age header. You can have a look at what Varnish Software's Drupal server issues:

    $ GET -Used http://www.varnish-software.com/|grep ^Cache-Control
Cache-Control: public, max-age=600

    https://github.com/varnishcache/varnish-cache/blob/master/doc/sphinx/users-guide/increasing-your-hitrate.rst

    • 2