Building a Rails Controller From Scratch by Alex Kitchens - YouTube

If you replaced ActionController with an implementation of your own, what would you have to build to get your app working again? In this talk, we'll do just that. We'll see how the controller interacts with the router to receive a request, process it, and return a response. We'll also rebuild controller features like Params, Controller Callbacks, and Rendering. In the end, we'll have a new functioning controller class called AwesomeController, and we will have seen what it takes to process a request in Rails.