nestjs-modules-services-controllers

Clean architecture in NestJS organizes features into separate modules, each containing a service for business logic, a controller for HTTP endpoints, and DTOs for validation. This structure separates concerns, improves testability, and scales as your API grows by keeping domain boundaries clear and dependencies injected through NestJS's built-in container.

Structure your TypeScript backend under src/modules with feature-first organization: each module (users, posts, auth) contains a controller handling HTTP requests, a service encapsulating business logic, and DTOs defining request/response shapes. This pattern follows RESTful conventions, centralizes validation, and makes dependency injection straightforward across your API.

Yes. Refactoring into separate feature modules involves extracting domain logic into dedicated services, grouping related controllers under module boundaries, defining DTOs for each feature's inputs and outputs, and reorganizing code under src/modules. NestJS's module system and dependency injection make splitting a monolith into clean, testable features straightforward.

Implement consistent RESTful patterns by standardizing HTTP methods (GET, POST, PUT, DELETE) in controllers, using DTOs to validate incoming requests, returning predictable response shapes, and handling errors uniformly across endpoints. NestJS controllers decorated with @Controller map routes, while services injected via dependency injection handle the actual logic.

DTOs (Data Transfer Objects) define the shape and validation rules for data entering and leaving your API endpoints. In modular NestJS design, each feature module defines its own DTOs, which controllers use to validate requests before passing data to services. This ensures type safety, consistent validation, and clear API contracts.

Consistent naming conventions improve readability and maintainability. NestJS modules typically follow feature names (users, auth, posts), services append .service.ts, controllers append .controller.ts, and DTOs append .dto.ts. This standardization, combined with src/modules organization, makes the codebase predictable and easier to navigate as it grows.