How to track down the cause of the upstream timed out error in Nginx?

Question

Nginx

There is a server on ubuntu apache + nginx. It has several sites and recently every day the server dies with the error "*46 upstream timed out (110: Connection timed out) while connecting to upstream". There were no special changes in the code, but each of the sites daily updates the information in itself, in the files on the server, etc. Restarting the server helps, but I do not have enough knowledge to understand how to identify the problem - there is access to error logs, access, but I do not see anything unusual there.

Advise sensible material or technique in order to understand which script is overloading the system. Sites are voluminous with many functions, and even if you understand which of them launches a harmful process, then it will again be unclear how to identify that very function inside this particular site.

Answer 1

apache+nginx

Let's get the details! And behind also PHP probably? If so, then look at his logs.