Extending Chassis

Chassis includes a flexible extension system to allow setting up the server exactly how you like.

Available Extensions

This is a non-exhaustive list of what’s available to drop into your Chassis box.

  • Memcache: Install a memcached server, and configure WordPress to use it automatically.
  • Redis: Install Redis server.
  • phpMyAdmin: Set up phpMyAdmin on your Chassis box
  • Tester: Install and configure PHPUnit, along with the WordPress additions so you can run plugin unit tests.
  • Theme Review: Set Chassis up for theme reviewing.
  • MailHog: A Chassis extension to install and configure MailHog on your server.
  • Cavalcade: Cavalcade is a replacement for WordPress’ built-in cron that runs as a daemon on your system. It horizontally scales in production to ensure your scheduled tasks keep up with the scale of your site.
  • XDebug: A Chassis extension to install and configure Xdebug on your server.
  • Query Monitor: A Chassis extension to install and configure your Chassis WP install to use Query Monitor to help with debugging.
  • Debugging: A Chassis extension to install and activate common WordPress plugins used for debugging during development.
  • NodeJS: A Chassis extension to install NodeJS.
  • Imagick: A Chassis extension to install ImageMagick.
  • Fish: A Chassis extension to install Fish Shell.
  • Composer: A Chassis extension to install PHP packages to install Composer.

Creating your own

Chassis extensions can be created by anyone who knows the Puppet configuration language.


“What’s Puppet?”, I hear you cry. Puppet is a tool that allows you to “provision” servers; that is, make them consistent by installing software packages and setting configuration. It also includes its own neat language for the configuration, giving it a huge amount of power.

Before you get worried that we’re crazy (although we might be), and that you’re learning something useless, Puppet is one of the most widely used tools for configuring servers, and has a huge community behind it. Everyone from Twitter to the New York Times to Google uses Puppet to set up their servers. Anything you pick up here is applicable in the wider Puppet ecosystem too for setting up your own servers.

Chassis internally uses Puppet to configure your virtual machine and set up all the niceties that you’ve come to expect from Chassis, such as switching PHP versions or configuring MySQL.

If you don’t already know Puppet, we recommend reading the Learning Puppet series, which guides you into understanding and using Puppet. We’ve already got Puppet set up and installed inside your Chassis virtual machine, so you can follow any of the steps by simply running puppet inside the box.

Once you’ve got a grip on Puppet, we’d recommend having a quick read of how Chassis works internally. We store all our files in the puppet/ directory.

Extensions are nothing more than a bit of convention and a Puppet manifest. An extension is essentially a subdirectory of extensions/ under your Chassis root directory, containing a chassis.pp Puppet manifest. This manifest is added to the Chassis manifests and run during a provision. It’s also loaded in at the same time as the rest of the Chassis Puppet files, so you can add your own configuration and set up resource dependencies as needed.

If you need to load PHP in, Chassis also automatically adds a require block for extensions/*/local-config.php. Simply create this file, or use Puppet to create it at /vagrant/extensions/<extension>/local-config.php and it’ll be loaded in via wp-config.php.

For an example of how it’s done, take a look at one of the existing extensions linked above. The memcache extension includes an example of how to install a PHP extension and automatically configure WordPress to use it, and is a very simple introduction to the system.

Example: Installing The Memcached Extension

To install the memcached extension you would do the following:

  1. Open your terminal and navigate to your root Chassis folder.
  2. git clone git@github.com:Chassis/memcache.git extensions/memcache.
  3. vagrant provision.