Quick Setup: Apache Worker, FastCGI, PHP-FPM and APC

I'm not going to go into great depths in this post, I'm mainly going to go through setting up Apache MPM Worker, PHP-FPM, FastCGI (mod_fastcgi, not mod_fcgid) and APC with an almost minimal configuration. I'm using Ubuntu 11.04 to demonstrate, though the steps should work for most Debian based, and generally most distro's apart from the package management and location of configuration files. I know 11.04 is a bit out of date but I'm waiting for Precise Pangolin to be released to upgrade to a LTS. This setup also allows the APC cache to be shared among PHP processes.

The point of all of this was to change away from Apache Prefork to Apache Worker as serving static files with mod_php running in a limited memory environment is devastating to available memory. I am quite happy with this set up so far, and haven't had problems with it at all.

It is much more common to see this set up with nginx rather than Apache, and I may go that route eventually but it is useful to not have to translate Apache configurations to nginx configurations when I am just testing something out, or someone else has to get their hands dirty.

Installing the necessary packages

On Ubuntu this is accomplished by:

sudo apt-get install apache2-mpm-worker libapache2-mod-fastcgi php5-fpm php-apc php5-gd

It will also cause a few other dependencies to be installed, and you need the multiverse repository enabled to get the FastCGI package. The GD library is not strictly necessary but it allows the APC status page to make its' graphs.

Apache Configuration

I found that mod_fastcgi was automatically enabled upon install, but just to be sure we enable it anyway, along with mod_actions which we will be using.

sudo a2enmod fastcgi actions

I added the following to /etc/apache2/httpd.conf, but I'm sure you could also add it to a specific virtualhost. I also created the directory /var/www/fastcgi, you may also have change its' ownership to be the same as the Apache or PHP-FPM processes so they can access the directory, it's usually www-data on Ubuntu. We are also using Unix sockets to connect to the PHP-FPM process as this has less overhead than going through the TCP/IP stack.

<IfModule mod_fastcgi.c>
        Alias /php5.fastcgi /var/www/fastcgi/php5.fastcgi
        AddHandler php-script .php
        FastCGIExternalServer /var/www/fastcgi/php5.fastcgi -socket /var/run/php-fpm.sock
        Action php-script /php5.fastcgi virtual
 
# This part is not necessary to get it to work, but it stops anything else from being
# accessed from it by mistake or maliciously.
        <Directory "/var/www/fastcgi">
                Order allow,deny
                <Files "php5.fastcgi">
                        Order deny,allow
                </Files>
        </Directory>
</IfModule>

In short it tells Apache to send all PHP files off to the PHP-FPM process. Seeing as we are using FastCGIExternalServer, FastCGI will let PHP-FPM do it's own process management.

PHP-FPM Configuration

We will be using the default process pool that is already set up, so we just need to change one line to tell PHP-FPM to listen for incoming connections on the same socket as we used in the Apache configuration. We are editing /etc/php5/fpm/pool.d/www.conf in this case.

; Find the line below
listen = 127.0.0.1:9000
; and change it to this:
listen = /var/run/php-fpm.sock

If you are in a low memory environment you will really want to adjust the process management settings. I left mine with dynamic process management and lowered the rest of the settings, if you don't set pm.start_servers, PHP-FPM will complain when you restart it, and set it to 20, which may be more than you need or have memory for.

PHP-FPM Status Page

If you want to see the status page for this PHP-FPM pool, you also need to uncomment the following 2 lines in /etc/php5/fpm/pool.d/www.conf:

pm.status_path = /status
ping.path = /ping

The status page contains a few lines of information about the process pool, such as active and idle processes, and accepted connections. My main use of it though is to check that the maximum number of children the pool can have has not been reached, which would mean that some request might have been denied as there were no spare processes.

To actually access the status page you will need to add the following to a virtualhost, within a directory:

<FilesMatch "^ping|status$">
          SetHandler php-script
</FilesMatch>

You can change ping and status to something else if you prefer but remember to change it in the pool configuration file and in the above snippet. I wouldn't put this somewhere publicly accessible but is useful to have around.

APC

APC should already be enabled after installing, we need to edit it's configuration file to set a larger memory limit and to use shared memory. The file in this case is /etc/php5/fpm/conf.d/apc.ini, and we add the following 2 lines:

apc.mmap_file_mask=/apc.shm.XXXXXX
apc.shm_size=96

This sets the memory limit to 96mb and makes APC use shared memory. In later versions of APC you may need to add a 'M' after the memory size setting or it will complain. While this has worked fine for me on normal Ubuntu installations, I had to edit /etc/fstab on our OpenVZ VPS and add the following:

none  /dev/shm    tmpfs   defaults    0    0

What is very useful when dealing with APC is to copy /usr/share/doc/php-apc/apc.php.gz to a web accessible folder and unzip it. It gives you an overview of how APC is doing and is very useful for troubleshooting, plus you get graphs. It should definitely not be publicly accessible. You will need to edit it to add a password if you want to be able to login to clear the cache but the file is well commented for that.

Using PHP-FPM along with APC will allow the APC opcode cache to be shared among all the PHP processes in the same pool. If you wish to use APC but are wary about sharing the APC opcode cache among different sites, simply create a new PHP-FPM process pool for each site and specify the pool in the relevant virtualhost. You can also specify most PHP configuration options on a per pool basis and run PHP as a different user or group per pool. You may even want to disable APC for a process pool if you wished.

Finishing Up

Issue the following command to restart PHP-FPM and Apache:

sudo service apache2 restart && sudo service php5-fpm restart

If everything went alright you should now be able to serve PHP files with a great reduction in memory usage over Apache Prefork. I couldn't produce a repeatable, significant performance difference in using Apache Worker and PHP-FPM over Prefork and mod_php, though my testing was by no means conclusive. I used ab to access a basic Drupal page, and a static HTML page and requests per second were improved on both given limited resources, but I seem to have mislaid the results.

As a final note you may be able to reduce your Apache processes size further by setting 'ThreadStackSize 192000' in apache2.conf but this can cause severe crashes of the webserver and corruption of requests, the amount you can reduce the thread stack size to depends on what modules your Apache setup is using and so changing this setting should be well tested before going into production. According to the Apache 2.2 documentation, 128000 is too low on Linux, and from my experience 136000 is also too low. Though using 192000 reduces our 64 bit Ubuntu VPS's Apache processes size from around 22mb each to around 8 - 10mb each without ill effect.

It also goes without saying you can reduce your Apache process size by disabling unneeded modules.

Thanks for reading, and hopefully see you another time. :)