NestJS Architecture: Modules, Services, and Dependency Injection

NestJS brings structure to Node backends with a module system, decorators, and dependency injection that scales with your team.

Modules organise the app

Each feature is a module that declares its controllers, providers, and imports. This makes boundaries explicit and dependencies traceable.

Services hold the logic

Controllers stay thin; they delegate to services that contain business logic. This separates HTTP concerns from the work itself.

Dependency injection for testability

Inject services into controllers and providers rather than constructing them manually. Swapping in mocks for tests becomes trivial.

Wrapping up

For growing backends, NestJS's opinions pay off: consistent structure, clear dependencies, and a codebase new developers can navigate.