NestJS Microservices

Transport Strategies

• Synchronous (RPC): Use gRPC for low-latency, internal service-to-service calls.
  • Why: 10x faster than REST/JSON, centralized .proto contracts.
• Asynchronous (Events): Use RabbitMQ or Kafka for decoupling domains.
  • Pattern: Fire-and-forget (emit()) for side effects (e.g., "UserCreated" -> "SendEmail").

Monorepo Architecture

• Contracts:
  • Pattern: Store all DTOs, .proto files, and Interfaces in a Shared Library (libs/contracts).
  • Rule: Services never import code from other services. They only import from contracts.
• Versioning: Semantic versioning of messages is mandatory. Never change a field type; add a new field.

Exception Handling

• Propagation: Standard HttpException is lost over Rpc/Tcp.

• Standard: Use RpcException and generic Filters.

  // Global RPC Filter
  @Catch()
  export class RpcExceptionFilter implements RpcExceptionFilter<RpcException> {
    catch(exception: RpcException, host: ArgumentsHost): Observable<any> {
      return throwError(() => exception.getError());
    }
  }
  

Serialization

• Message DTOs: Use class-validator just like HTTP.
  • Config: Apply useGlobalPipes(new ValidationPipe({ transform: true })) in the MicroserviceOptions setup, not just HTTP app setup.