A few days ago, I published a blogpost called A better way to run PHP-FPM. It's gotten a fair amount of attention. It detailed the use of the "ondemand" process manager as well as using a separate PHP-FPM master per pool, for a unique APC cache.
The setup works fine, but has the downside that you'll have multiple masters running -- an obvious consequence. Kim Ausloos created a solution for this by using systemd's socket activation. This means PHP-FPM masters are only started when needed and no longer stay active on the system when obsolete.
This has a few benefits and possible downsides;
- Pro: masters are only spawned when needed, meaning less memory consumed overall
- Pro: masters are also killed when they're obsolete, so a perfect ondemand scenario
- Min: no longer able to restart a PHP-FPM pool when needed (to load new .INI settings), all pools would restart?
- Min: APC cache will be destroyed whenever a PHP-FPM master is killed (which may not be a bad thing, for low-traffic sites)
I'll do some more testing on this use-case, as well as the performance penalty (if any) of having to start new master on a first request to the PHP-FPM socket. For this to work out, RHEL or CentOS 7 is needed in my case (we're a RHEL/CentOS shop), as systemd is required and will only be supported from RHEL/CentOS 7.