There's been a lot of talk recently regarding the integration of the Symfony2 components, as a fundamental part of Drupal 8's core system. I won't rabble on repeating the many things that have already been said elsewhere; however, to quote the great Bogeyman himself, let me just say that "I think this is the beginning of a beautiful friendship".

On a project I'm currently working on, I decided to try out something of a related flavour. I built a stand-alone app in Silex (a sort of Symfony2 distribution); but, per the project's requirements, I also managed to heavily integrate the app with an existing Drupal 7 site. The app does almost everything on its own, except that: it passes its output to drupal_render_page() before returning the request; and it checks that a Drupal user is currently logged-in and has a certain Drupal user role, for pages where authorisation is required.

The result is: an app that has its own custom database, its own routes, its own forms, its own business logic, and its own templates; but that gets rendered via the Drupal theming system, and that relies on Drupal data for authentication and authorisation. What's more, the implementation is quite clean (minimal hackery involved) – only a small amount of code is needed for the integration, and then (for the most part) Drupal and Silex leave each other alone to get on with their respective jobs. Now, let me show you how it's done.