Switching Apache2 to php-fpm for performance

there are many articles on the internet telling you to switch from Apache & mod_php to nginx to get better performance.

However the main reason for performance improvement is not nginx itself but rather the way it integrates PHP.

Different ways to integrate PHP

Apache traditionally used mod_php to embed the PHP interpreter inside Apache HTTP request handler. This way it can directly interpret PHP scripts whereas with CGI it would have to start a new PHP interpreter process first – per request.

The drawback however is that the PHP interpreter is embedded in all request handlers – even those that just serve static files. This obviously blows up memory consumption which in turn can lower performance.

Nginx on the other hand uses the FCGI approach where a pool of PHP processes is started along the webserver using the FCGI process manager, FPM. The webserver then delegates individual requests using the FCGI protocol as needed.
This avoids the PHP interpreter startup costs as well as starting it without a need and is the reason nginx is faster then mod_php.

However since Apache 2.4 one can also use FCGI to integrate PHP and get virtually the same characteristics like nginx. Sticking with Apache saves you migrating all the .htaccess rules and means an easier setup for many webapps.

Furthermore since Apache 2.4.10 one can use mod_proxy_fcgi for a reverse-proxy configuration which further reduces the occupied PHP workers in the FPM pool for better performance.

Configuration on Ubuntu 16.04

Switching to FCGI on Ubuntu 16.04 is quite easy. The needed module are installed by default and just need to be enabled:

a2enmod proxy_fcgi && a2dismod php7.0

Then inside your-site.conf add

 # PHP-FPM
 <FilesMatch "\.php$">
     SetHandler "proxy:unix:/var/run/php/php7.0-fpm.sock|fcgi://localhost/"
 </FilesMatch>
 <Proxy "fcgi://localhost/">
 </Proxy>

this connects Apache in reverse proxy mode to the PHP-FPM pool using unix domain sockets for optimal performance. See the Apache Wiki for details.

Note that php-fpm by default only creates 5 PHP worker processes, which in turn limits the maximal simultaneous connections. You might want to raise this by adaptingĀ pm.max_children inĀ /etc/php/7.0/fpm/pool.d/www.conf.

Typically you set this to RAM size / avg. process size. You can find out the latter via:

ps -ylC php-fpm7.0 --sort:rss

Performance Measurements

To measure the results I did a force reload of my single user Nextcloud instance and measured the Load time via Chrome developer tools:

Page mod_php mod_proxy_fcgi
Files 701 ms 605 ms 0.86
News 1.77 s 1.67 s 0.94

as one can see depending on the amount of static/ dynamic files and internal/ external requests we can bring down the page load time by up to 15%.