I have a Linux server running Nginx and from time to time it starts throwing a 502 error when trying to access it throw HTTP, and after a while gets back to normal.
I've checked the different logs (Nginx, PHP and MySQL) and didn't find anything that could help me find what's causing this.
Any idea where I should look or if it's possible to set any logging/monitorinh tool to help me out?
Thanks,
502 is a Bad Gateway error. You may want to use a log monitoring tool to see these types of errors. You may also want to send the PHP errors to see if they are generating fatal errors at the same time. I personally use Loggly for this purpose, but you can use other tools available in the market.
Also, I would recommend logging Nginx as JSON, and adding to the normal metrics, the uptime for the upstream servers, so that you can see if the 502 errors are also correlated with deteriorating performance.
If you haven't read this already, I recommend starting here:
https://www.nginx.com/resources/admin-guide/logging-and-monitoring/