random 502 gateway errors with nginx php-fpm and ubuntu

Question

I was having an issue with random 502 gateway errors using nginx and php-fpm. In my case I discovered a scenario where various php.ini error_log settings and error_reporting lev

Answer 1

502 gateway errors in Nginx are caused by php-fpm not having enough process and/or timeouts. Logging only tells you what the issues are and are not the cause of 502 errors.

I use stunnel+haproxy+nginx+php-fpm on 25 servers. The defaults in pfp-fpm are very low, even for a moderately busy server. Configure the fpm child processes much the same way you would with apache mod_php.

I use the following:

pm.max_children = 250
pm.start_servers = 20
pm.min_spare_servers =10
pm.max_spare_servers = 20
pm.max_requests = 1500

This is a server with 2GB ram. It serves 20-30GB traffic per day with no 502's

Answer 2

I've run into this on windows machines running iis and php in fastCGI mode so it isn't just a nix problem.

The culprit was php logging as well. You don't have to set it to a static directory though if you grant proper permissions it can write to the same directory that the script resides in. (Can be very helpful if you have a large and complicated site)

My server is setup this way and I just added a rule to not serve the error logs to the public.

To sum it up, CHECK PERMISSIONS! =)

Answer 3

I have a similar problem that resolved by disabling PHP warnings, however, I think the problem has something to do with NGINX configuration of the buffers which the error logging uses. The error only triggers after a certain number of warning messages are queued, and seems to be quite predictably repeatable; but I can't figure out what settings are involved so have shut off the warnings until I can resolve the settings that are broken.

Answer 4

If above steps don't help you solve your issue, check if you have eaccelerator enabled.

Disable it globally by disabling the load .so entry in either your php.ini or php.d/eaccelerator.ini

All problems are gone. Seems like the accellerator fails in certain situations in combination with php-fpm.