PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation with some additional features useful for sites of any size, especially busier sites.
Source : PHP-FPM Website
PHP-FPM is far better than the standard mod_php implementation of PHP and also easier to implement that spawn-fcgi. PHP-FPM works like an application that loads and kills PHP instances as needed. Of all the benefits that it offers, reduced memory usage is the most attractive one.
Step 1 : Add the Dotdeb repository
You can skip this step if you have already added the Dotdeb repository while installing NGINX on your Rackspace Debian Cloud Server. The version of PHP and PHP-FPM in the Dotdeb repository is up-to-date and stable. We need to grab the latest version of PHP to benefit from all new updates and bug fixes. Read this article on adding the Dotdeb repository to your Debian Squeeze Server.
Step 2 : Installing PHP and PHP-FPM
The following command will do it all for you. I have included some popular PHP modules. You can choose and install the modules that you require.
sudo apt-get install php5-cgi php5-cli php5-common php5-curl php5-dev php5-fpm php5-gd php5-idn php5-imagick php5-imap php5-json php5-mcrypt php5-memcache php5-mhash php5-ming php5-mysql php5-ps php5-pspell php5-recode php5-snmp php5-sqlite php5-suhosin php5-tidy php5-xcache php5-xmlrpc php5-xsl php-pear php-soap
This command will install PHP-FPM and auto start the service. PHP-FPM will get added to the startup.
Step 3 : Configuring and Optimising PHP
As you will be using PHP-FPM to process PHP scripts, edit the php.ini file that can be found at /etc/php5/fpm/php.ini. There are a lot of PHP settings that you can configure to optimise PHP for performance, speed and security. The following three are a good starting point.
memory_limit = 64M expose_php = Off display_erros = Off
Step 4 : Configuring and Optimising PHP-FPM
Remember, we are setting up a low-end (256MB) web server on Rackspace. We need to conserve as much memory as possible. Edit the file /etc/php5/fpm/pool.d/www.conf
pm = dynamic pm.max_children = 10 pm.start_servers = 1 pm.min_spare_servers = 1 pm.max_spare_servers = 4 pm.max_requests = 500
This will bring down the number of children processes and free up some RAM.
Step 5 : Restart PHP-FPM
service php5-fpm restart
This command will restart PHP-FPM.