Go2Linux posted a tutorial about configuring varnish logs (varnishnsca), logrotate and awstats

OK, you now have varnish installed on your server and you started to catch the pages on it, so your webserver is now missing the hits to your pages.
Well, that is great for your webserver load, but not too good for your statistics analysis, because /var/log/apache/access_log will miss the hit.

  Configure varnish logs (varnishnsca), logrotate and awstats