Much like the Apache Worker MPM, mod_spdy is a multithreaded module, and processes multiple SPDY requests from the same connection simultaneously. This poses a problem for other Apache modules that may not be thread-safe, such as mod_php. Fortunately, it is fairly easy to adjust your Apache configuration to make your existing PHP code safe to use with mod_spdy (and with the Worker MPM as well).
Check your current PHP setup
If you are running a site with PHP, there are two common setups. The first is to use mod_php, with the Apache Prefork MPM. The second is to use mod_fcgid. As when using the Worker MPM, when using mod_spdy it is important to use this second setup.
To quickly check which setup you are currently using, run the
apache2ctl -M (or
httpd -M on some
systems), which will list all the Apache modules you have installed. If you
see something like
php5_module in the list, you are using
mod_php, and will need to adjust your setup for use with mod_spdy. If you
don't see that but instead you see
fcgid_module in the list,
then it is probably already safe for you to install and use mod_spdy.
Configure PHP for use with mod_spdy
Configuring PHP to work with mod_spdy is very similar to configuring PHP to work with the Worker MPM. Instead of using mod_php, you can use mod_fcgid which manages separate processes dedicated to running PHP.
To switch to PHP via mod_fcgid, follow the Apache mod_fcgid example (scroll down a bit on that page, to the PHP example).
It's important to also uninstall or disable mod_php as part of making the switch to mod_fcgid, since it's now mod_fcgid that's responsible for running PHP. On Ubuntu:
sudo a2dismod php sudo apt-get install php5 php5-cgi libapache2-mod-fcgid
Then add the following to your httpd.conf, which tells Apache to route requests for PHP scripts to mod_fcgid (this is a simplified version of the Apache mod_fcgid example linked to above):
<Location /> AddHandler fcgid-script .php Options +ExecCGI FcgidWrapper /usr/bin/php-cgi .php </Location>
Restart Apache and you should now be serving PHP via mod_fcgid, in a way that's compatible with mod_spdy or with the Worker MPM.
There are some additional mod_fcgid configuration details that you may want to read about in the Apache mod_fcgid example documentation.