service-layer-extractor

To refactor fat controllers into a service layer, you move business logic from routes and controllers into dedicated services. This separation of concerns improves backend readability and enables isolated unit testing through dependency injection.

The best way to migrate business logic is using a phased migration strategy with tests. You refactor endpoints incrementally, such as moving a user signup flow to a UserService, while wiring controllers to the new services and validating with unit tests.

You need dependency injection when separating business logic into services to enable isolated unit testing. By defining service interfaces and wiring dependencies, you establish clear layer boundaries that make your backend codebase scalable and maintainable.

A scalable backend folder layout separates concerns into routes, controllers, services, repositories, and models. This structured architecture ensures clear boundaries between request handling, business logic, and data access.

Yes, you can apply a service layer migration strategy to existing codebases with fat controllers. The approach provides a structured folder layout and a phased migration plan, allowing you to incrementally refactor complex controllers into testable services.