Send 502 when all php-fpm workers are in use

[justink101]

Starting php-fpm: [07-Jul-2014 17:52:33] WARNING: [pool app-execute]
listen.backlog(0) was too low for the ondemand process manager. I updated it
for you to 128

Well that is unfortunate, not sure why using on-demand required a backlog of
128. Essentially this php-fpm pool runs jobs then the workers automatically
exit. So essentially they spawn run and die.

pm = ondemand
pm.max_children = 100
pm.process_idle_timeout = 3s;

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,251476,251519#msg-251519