So as you guys said: it's a normal behavior of nginx and the problem is how can I monitor response time exactly?because, when I request a static link (a jpeg i.e), it take about 3s to completely download, but request_time still 0.000, and because it's a HIT request so I dont have upstream_response_time too. What metric or method that I should use to monitor my nginx reponse time performance?

Thanks for quickly reply