Moving a Rails/Mongrel site to Phusion Passenger on Ubuntu

As I’ve noted before, several of our Rails projects are hosted using Phusion Passenger. We’ve been helping HitFix explore this option in recent weeks because it solves several minor deployment and restart frustrations they’ve been grappling with, and in the process I wrote up this walk-through for the installation.

This process is actually really easy and the instructions on the Passenger site and those provided during the installation process are excellent. The glitch we ran in to is that recent versions of Ubuntu and/or Apache 2.2.x use a slightly different method of loading modules and module configuration. (I haven’t run in to this method often enough to have learned whether it’s new in Apache or in Ubuntu.)

Instead of using one monolithic configuration file, sometimes offloading host configuration to included files, these Apaches instead globally include all modules found in the mods_enabled subdirectory of the Apache directory. Each module has two files, a .load file and a .conf file. The .load file contains only the LoadModule configuration directive; the .conf file contains any configuration directives.

Now, the actual files live in the mods_available subdirectory of Apache, and activating a module just means adding a symlink to the relevant files in mods_enabled, then restarting Apache. Deactivating it just means removing the symlink and restarting again.

With that in mind, here’s the Passenger process:

• Install Passenger on the server. This should be as simple as:

sudo gem install passenger
sudo passenger-install-apache2-module

• On one system, this second command actually told me that the Apache 2 Development Headers were missing. (Passenger needs these to compile the Apache module.) I needed to run sudo apt-get install apache2-prefork-dev to get these headers. This didn’t work on the first attempt, but running sudo apt-get update once or twice finally got me a successful install of that package. Running the passenger-install-apache2-module script then worked successfully. Note that you will need a compiler on the system in order to generate the Apache module. You would think you could take this for granted, but apparently not.

At this point, the module is built. This is where we have to adapt Phusion’s original installation instructions. Essentially, the next step is to make sure the module is loaded by Apache. Here’s how I did this:

• Create a file at /etc/apache2/mods-available/passenger.load with the following content:

LoadModule passenger_module /usr/lib/ruby/gems/1.8/gems/passenger-2.0.6/ext/apache2/mod_passenger.so

• Create a file at /etc/apache2/mods-available/passenger.conf with the following content (I think the IfModule container may be optional, but I played safe):

<IfModule passenger_module>
PassengerRoot /usr/lib/ruby/gems/1.8/gems/passenger-2.0.6
PassengerRuby /usr/bin/ruby1.8
</IfModule>

• Create symbolic links to both those files from /etc/apache2/mods-enabled/, i.e.

sudo ln -s /etc/apache2/mods-available/passenger.load /etc/apache2/mods-enabled/
sudo ln -s /etc/apache2/mods-available/passenger.conf /etc/apache2/mods-enabled/

We can restart Apache at this point without disturbing the existing site. Note that we can change which ruby is used (e.g. for Ruby Enterprise Edition) by altering the path at the PassengerRuby directive and restarting Apache.

To move a site to Passenger, you want to back up the file found at /etc/apache2/sites-available/yoursite, then edit it to make these changes:

• Change the DocumentRoot to the public directory of the app, e.g. DocumentRoot /u/apps/yoursite/current/public
• Comment out (with a #) all the lines related to the proxy, starting with the Proxy balancer definition and extending through all the ProxyPass, ProxyPassReverse and ProxyPreserveHost directives.
• Restart Apache (/etc/init.d/apache2 restart). If something goes wrong, restore the backup you made of the configuration file and restart Apache again to restore the previous configuration.

The final trick is to update the restart task in Capistrano to handle restarting Passenger and not Mongrel. This is actually pretty easy, particularly if you’ve already overloaded the restart task in your config/deploy.rb file. Just replace the line reading run "mongrel_rails cluster::restart -C #{mongrel_config}" with one reading run "touch #{current_path}/tmp/restart.txt" and we’re good to go. The start and stop tasks probably also needs tweaking to remove the mongrel commands–probably pasting the same command in for “start” will do the trick unless we feel like putting Apache commands in.