When my website receives many requests per second (I assume at least 80 requests per second), the server randomly blocks some requests with 502 Bad Gateway nginx-errors. This happens every few seconds: All requests are blocked and you can't even view the website after a quick refresh. But then again, three seconds later, everything is back to normal.
The site is in general very fast, even during these weird phases. It doesn't lag or anything - it just randomly blocks connections.
The error messages seem to appear for everyone at the same time. So I assume that there is some kind of timed max_connection limit or something which quits the service for a few seconds.
I've tried everything that came up to my mind:
Checking ulimits (Soft & Hard are both at about 50,000),
nginx worker_connections raised to 8,192 (from 4,094)
and doubled max_connections in my mysql settings.
Still without any effect.
Also I tried to look through every error log on my server (nginx, httpd, mysql etc.), but I couldn't find anything useful. Though maybe I'm missing an important log... they're quiet hard to find and I don't really know what to look for.
Is there anything I could try?
I can also provide several .conf files, if necessary.
