What are modules, controllers and services?

Definition:

Nest modules define feature boundaries and register the controllers and providers that belong to a feature. Controllers handle transport concerns, while services usually contain business rules. This separation makes code easier to reuse and test without tying every decision to HTTP.

Key points:

• A module groups a feature and declares its dependencies.

• A controller handles HTTP input and responses.

• A service holds business logic; keep controllers small.

• Keep database and business operations out of large controllers; a service can also be called by a job or scheduled task.

Interview point:

• A module describes dependency visibility; it is more than a folder that holds related files.