Low server response speed (WAIT 2-5 sec) - where to dig and how to solve?

Question

Nginx

In short:
- clean Centos 7
installed - VestaCP panel installed (nginx face, httpd under the hood)
- config: 1 core - 3Ghz / 2GB RAM/20GB HDD (Raid10, no drawdown by IOPS
) special load
A problem has been detected - the server response speed is from 2 to 5 seconds (namely WAIT).
Further (as the problem was discovered) nginx was tuned (under 1 core, smaller compression and other trifles, so that the processor ate less).
The problem never went away.
Where to dig, what could be the matter?

Answer 1

What is weight and how do you test

Answer 2

I agree with nirvimel that you need to watch $upstream_response_time. If the backend's response time is about the same as the wait time, it's worth looking at what it's doing.
Most often in such cases, the backend is to blame. Especially if there is some kind of Joomla (well, yes ... I don’t like it), you will have to get into the giblets and see where everything is (then php-xdebug + qcachegrind in hand).