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Date: Thu, 18 Oct 2012 14:39:41 -0700
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To: Reinis Rozitis <r@roze.lv>
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Subject: Re: [PHP-DEV] [RFC] Socket activation support for PHP-FPM
From: david@davidstrauss.net (David Strauss)

On Thu, Oct 18, 2012 at 2:03 PM, Reinis Rozitis <r@roze.lv> wrote:
> What would be the advantage on using systemd instead of using FPMs native
> 'ondemand' process manager?

The ondemand process manager still keeps considerable memory
allocated, and PHP-FPM currently has some idle CPU load (<1% per
service, but it adds up when you manage 500+ pools on a box) when not
processing requests.

The ondemand process manager doesn't solve the dependency issue
mentioned in the RFC (a web server requiring PHP-FPM to be ready) or
allow privileges to be dropped before PHP-FPM gets invoked at all. The
latter is useful for platform providers that let users configure
PHP-FPM for their individual use cases but want to provide assigned
"listening" sockets.

Socket activation also supports replacing the entire binary (as with a
PHP-FPM security update) without interrupting listening on the socket.
PHP-FPM supports reloading to a limited degree, but I don't think it's
possible to fully replace the executable.

There is also work underway to have socket activation on the base
system spawn or start full containers (like LXC) on-demand. Since
PHP-FPM will, itself, be in the container, something else needs to
listen on its behalf.

Finally, it's a platform consistency issue. As more services move to
socket activation in Fedora and Red Hat, socket units will become a
sort of "common currency" for configuring which services listen where.

-- 
David Strauss
   | david@davidstrauss.net