Nginx – Getting 502 Bad Gateway, php-fpm takes 100% cpu

I am running a very similar set up (nginx 0.7.61, php+fpm 5.2.10) and my PHP processes never die, even after being idle.

The process control bits of my php-fpm.conf are as follows:

<value name="pm">
    <value name="style">static</value>
    <value name="max_children">3</value>
    <value name="apache_like">
        <value name="StartServers">20</value>
        <value name="MinSpareServers">5</value>
        <value name="MaxSpareServers">35</value>
    </value>
</value>
<value name="request_terminate_timeout">0s</value>
<value name="request_slowlog_timeout">0s</value>
<value name="slowlog">logs/slow.log</value>
<value name="rlimit_files">1024</value>
<value name="rlimit_core">0</value>
<value name="chroot"></value>
<value name="chdir"></value>
<value name="catch_workers_output">yes</value>
<value name="max_requests">500</value>

Note that while I have the apache-like bits defined (they were part of the default config), they aren't used because I have PM style static set.

You can turn up the logs to debug level using this in the global options section:

<value name="log_level">debug</value>

to see if there's a reported reason that it's shutting down workers.

A latch-ditch fix if this doesn't work would be to have a service like pingdom hit a php on your site every x minutes, but my experience with this software combo doesn't suggest that this should be required.

I think your max_children is too low

<value name="max_children">3</value>

Also you can try switching from TCP port to unix socket for php-fpm:

php-fpm.conf

<value name="listen_address">/tmp/php.sock</value>

nginx.conf

fastcgi_pass unix:/tmp/php.sock;

Elaborated:

1. Unix sockets are ~20% faster
2. You don't use time-wait sockets for each connect