NOTE: This article was written in 2005. For more up-to-date information on deplyoment, please see http://dev.catalyst.perl.org/wiki/deployment

In today's entry, I'll be talking about deploying an application in production using Apache and mod_perl.

mod_perl is the best solution for many applications, but I'll list some pros and cons so you can decide for yourself. The other production deployment option is FastCGI, which I'll talk about in a future calendar article.

mod_perl is very fast and your app will benefit from being loaded in memory within each Apache process.

If you need to run several Catalyst apps on the same server, mod_perl will share the memory for common modules.

Since your application is fully loaded in memory, every Apache process will be rather large. This means a large Apache process will be tied up while serving static files, large files, or dealing with slow clients. For this reason, it is best to run a two-tiered web architecture with a lightweight frontend server passing dynamic requests to a large backend mod_perl server.

Any changes made to the core code of your app require a full Apache restart. Catalyst does not support Apache::Reload or StatINC. This is another good reason to run a frontend web server where you can set up an ErrorDocument 502 page to report that your app is down for maintenance.

It is not possible to run two different versions of the same application in the same Apache instance because the namespaces will collide.

Now that we have that out of the way, let's talk about setting up mod_perl to run a Catalyst app.

You should install the latest versions of both Catalyst and Catalyst::Engine::Apache. The Apache engines were separated from the Catalyst core in version 5.50 to allow for updates to the engine without requiring a new Catalyst release.

Both Apache 1.3 and Apache 2 are supported, although Apache 2 is highly recommended. With Apache 2, make sure you are using the prefork MPM and not the worker MPM. The reason for this is that many Perl modules are not thread-safe and may have problems running within the threaded worker environment. Catalyst is thread-safe however, so if you know what you're doing, you may be able to run using worker.

In Debian, the following commands should get you going.

    apt-get install apache2-mpm-prefork
    apt-get install libapache2-mod-perl2

Every Catalyst application will automagically become a mod_perl handler when run within mod_perl. This makes the configuration extremely easy. Here is a basic Apache 2 configuration.

    PerlSwitches -I/var/www/MyApp/lib
    PerlModule MyApp

    <Location />
        SetHandler          modperl
        PerlResponseHandler MyApp
    </Location>

The most important line here is PerlModule MyApp. This causes mod_perl to preload your entire application into shared memory, including all of your controller, model, and view classes and configuration. If you have -Debug mode enabled, you will see the startup output scroll by when you first start Apache.

For an example Apache 1.3 configuration, please see the documentation for Catalyst::Engine::Apache::MP13 [1].

That's it, your app is now a full-fledged mod_perl application! Try it out by going to http://your.server.com/.

You may not always want to run your app at the root of your server or virtual host. In this case, it's a simple change to run at any non-root location of your choice.

    <Location /myapp>
        SetHandler          modperl
        PerlResponseHandler MyApp
    </Location>

When running this way, it is best to make use of the uri_for method in Catalyst for constructing correct links.

Static files can be served directly by Apache for a performance boost.

    DocumentRoot /var/www/MyApp/root
    <Location /static>
        SetHandler default-handler
    </Location>

This will let all files within root/static be handled directly by Apache. In a two-tiered setup, the frontend server should handle static files. The configuration to do this on the frontend will vary.

--Andy Grundman

https://metacpan.org/module/Catalyst::Engine::Apache::MP13