Twelve-Factor WordPress App #2: Dependencies

Factor #2: Dependencies

Explicitly declare and isolate dependencies

With Codebase out of the way, we’re already getting into unknown territory for WordPress.

Most programming languages offer a packaging system for distributing support libraries, such as CPAN for Perl or Rubygems for Ruby.

The packaging/dependency system for PHP is Composer.

A twelve-factor app never relies on implicit existence of system-wide packages. It declares all dependencies, completely and exactly, via a dependency declaration manifest.

In the world of Composer, the dependency declaration manifest is a composer.json file in the root of your project. At its core it’s just a JSON file that lists out all your dependencies and their versions. WordPress Plugins are also dependencies but by default there’s no explicit declaration of them. The solution to this is to manage your plugins via Composer. This means the plugins are also Composer packages.

One benefit of explicit dependency declaration is that it simplifies setup for developers new to the app. The new developer can check out the app’s codebase onto their development machine, requiring only the language runtime and dependency manager installed as prerequisites.

Once again in the world of Composer, this means that after a developer has checked out/cloned your codebase, they only need to run composer install. This simplifies developer on boarding time and makes for faster collaboration.

In Practice

Using Composer, especially with WordPress, is a massive topic on its own. Thankfully I’ve already addressed this in a blog post and screencast.