Version is the latest?
varnishlog, varnishncsa, varnishd can be accessible and available
// Log when failed due to not enough permission /etc/varnish$ varnishstat ..... Could not get hold of varnishd, is it running?
default.vcl difference should be tested
(Cache Hit rate) User agent normalization
e.g. If the cache is for API, response should be same for ALL user agents.
e.g. Cache for iPhone6 and 7 should be same.
