Project Layout

src/
  app.module.ts
  main.ts
  common/
    guards/jwt-auth.guard.ts
    interceptors/logging.interceptor.ts
    pipes/parse-int.pipe.ts
    filters/http-exception.filter.ts
    middleware/request-logger.middleware.ts
  users/
    users.module.ts
    users.controller.ts
    users.service.ts
    dto/create-user.dto.ts
    dto/update-user.dto.ts
    entities/user.entity.ts
    repo/user.repo.ts
  auth/
    auth.module.ts
    auth.service.ts
  graphql/
    users.resolver.ts
  micro/
    micro.module.ts
    micro.client.ts
test/
  users.controller.spec.ts

High-level diagrams

Request/Response pipeline

Client
  │  HTTP
  ▼
[Nest Application]
  │
  ├─(1) Middleware           ← before routing (per module or global)
  │
  ├─(2) Guards               ← canActivate? if false => 403
  │
  ├─(3) Pipes                ← validate/transform params & body
  │
  ├─(4) Interceptors ─────┐  ← before/after handler (logging, mapping, cache)
  │                        │
  ├─(5) Controller handler ├── calls → Service → Repository/DB/Clients
  │                        │
  └─(6) Exception Filters ◄┘  ← catch/shape thrown exceptions

Layer mapping

Presentation: Controllers, Resolvers (GraphQL), DTOs (as request contracts)
Application: Services (use cases), Guards, Pipes, Interceptors
Domain: Entities, business rules
Infrastructure: Repositories, external clients (DB, microservice, HTTP/gRPC), Middleware
Config/Composition: Modules (wire everything), main.ts (bootstrap)

1) Modules (composition layer)

The basic building block in NestJS applications.
Every application has at least one root module (AppModule).
Modules group related components (controllers, providers, services) and help organize code into cohesive units.