502 Gateway Errors under High Load (nginx/php-fpm)

This should fix it...

You have:fastcgi_buffers 4 256k;

Change it to: fastcgi_buffers 256 16k; // 4096k total

Also set fastcgi_max_temp_file_size 0, that will disable buffering to disk if replies start to exceeed your fastcgi buffers.

nginx centos php

Unix socket accept 128 connections by default. It is good to put this line into /etc/sysctl.conf

net.core.somaxconn = 4096

nginx centos php

If it's not helping in some cases - use normal port bind instead of socket, because socket on 300+ can block new requests forcing nginx to show 502.

CodeHunter