When you’re building an API, things start simple. But before you know it, there’s logic to reuse, from authentication to validation. This usually means a confusing list of before_actions. But there is a solution: moving from convoluted controllers to robust, maintainable chains of middleware. When you’re building an API, things start off simple. But before you know it, there’s lots of logic you want to build abstractions around and reuse - for example authentication, input validation and pagination. This usually means having a long list of callbacks living in your ApplicationController using Action Controller’s before_action magic. This leads to: tangled data dependencies (where callbacks depend on data retrieved by other callbacks and stored in instance variables - the authenticated user, for example) hidden behavior (all those excepts and only on your before_actions are hard to reason about and separated from your code, usually living in ApplicationController!) difficulties with testing (unit testing methods inside a controller is hard!) The middleware pattern can help us to bring sanity to our APIs and make them miles more maintainable This pattern, used by Elixir’s Phoenix, Node’s Express and even Ruby’s Rack helps us to untangle our data dependencies, make our code much more explicit and easily unit test complex behavior. We can apply this pattern to our Rails application to move faster and write more maintainable code. In this talk, you’ll learn how to move from convoluted controllers to robust, maintainable and well-tested chains of middleware built using an open-source gem, Coach (https://github.com/gocardless/coach). Each middleware can do exactly one job - for example, authenticating a user or validating input - and then either send a response to the client (for example an “invalid access token”) error or it can pass data along (for example the authenticated user) and call the next middleware. This talk is based on a blog post I wrote, “When good controllers go bad: getting started with Coach” (https://gocardless.com/blog/getting-started-with-coach/).