How to debug VCL in varnish?

Question

How can I print a log in VCL?

Can I print log info on screen?

Can I do like this?

sub vcl_recv {
  ....
  log.info(req.http.host         


        

Answer 1

Using a vcl config file, import the additional included "standard library", which includes a bunch of utility functions:

import std;

# To 'varnishlog'
std.log("varnish log info:" + req.host);

# To syslog
std.syslog( LOG_USER|LOG_ALERT, "There is serious trouble");

v6.x - https://varnish-cache.org/docs/6.0/reference/vmod_generated.html#void-log-string-s

v5.x - https://varnish-cache.org/docs/5.0/reference/vmod_std.generated.html?#func-log

v4.x - https://varnish-cache.org/docs/4.0/reference/vmod_std.generated.html?#func-log

v3.x - https://varnish-cache.org/docs/3.0/reference/vmod_std.html#log

See also man varnishlog