Pros¶

Speed

mod_perl is fast, and your entire app will be loaded in memory within each Apache process.

Shared memory for multiple apps

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

Cons¶

Memory usage

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.

Reloading

Any changes made to the code of your app require a full restart of Apache. 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.

Cannot run multiple versions of the same app

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

Cannot run different versions of libraries

If you have two different applications which run on the same machine, and each application needs a different versions of a library, the only way to do this is to have per-vhost perl interpreters (with different library paths). This is entirely possible, but nullifies all the memory sharing benefits that you get from having multiple applications sharing the same interpreter.

2. Install Apache with mod_perl¶

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

3. Configure your application¶

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.

Also, there have been reports that the block above should instead be (but this has not been confirmed):

    <Perl>
        use lib '/var/www/MyApp/lib';
        use MyApp;
    </Perl>
    <Location />
        SetHandler          modperl
        PerlResponseHandler MyApp
    </Location>

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

Test It¶

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

Non-root location¶

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 file handling¶

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.

Note the path of the application needs to be stated explicitly in the web server configuration for this recipes.