It's possible to have the same speed of delivering features over time and the "Fearless Refactoring: Rails Controllers" book will teach you how. This book contains a distilled knowledge taken from reliable architectures, like DDD, Hexagonal Architecture, DCI. I spend years researching those topics with one goal. Make your application better, simply, step-by-step, under control. I took what's best from the popular architectures, got rid of things that don't fit well with the Rails specifics and prepared recipes how to deal with a messy Rails code. Who has time to stay on top of all the latest articles, ideas, and code samples? You need good, working, easy to change code. This book is a step-by-step guide how to introduce a service layer in your existing Rails app. Every step is described in every detail, with code changes. All of that, so that you can safely refactor your codebase, even without a full test coverage.