Varnish可以输出到日志里面，下面是varnish3.x的写法

import std;
# To 'varnishlog'
std.log("varnish log info:" + req.host);
# To syslog
std.syslog( LOG_USER|LOG_ALERT, "There is serious troble");

varnish的日志通过varnishlog命令查看，可以加参数，只看某种url请求的，比如:

varnishlog -m 'RxURL:^/drupal$'

跟多参数查看varnish官网

https://www.varnish-cache.org/docs/3.0/reference/varnishlog.html