Async Nestjs Patterns

Async NestJS Patterns

Implement asynchronous flows, event-driven workflows, queues, microservices, and real-time WebSockets in a NestJS/TypeScript backend.

Use this skill when

• Wiring async/await with RxJS Observables (interceptors, guards)
• Building event-driven flows with @nestjs/event-emitter
• Implementing background jobs with Bull/BullMQ queues
• Adding microservices transport (TCP, Redis, NATS)
• Building WebSocket gateways for real-time features
• Implementing async lifecycle hooks (OnModuleInit, OnModuleDestroy)

Do not use this skill when

• The task is project structure / hexagonal layers → use hexagonal-nestjs-patterns
• The task is performance profiling → use performance-audit
• The task is Python async → use async-python-patterns
• The task is React async → use async-react-patterns

🎯 Core workflow

1. Decide async/await vs RxJS — load references/async-vs-rxjs.md to pick the right primitive.
2. Interceptors/pipes/guards — load references/interceptors-pipes.md when wiring middleware.
3. Event-driven — load references/event-driven.md for @nestjs/event-emitter and event design.
4. Background jobs — load references/queues.md for Bull/BullMQ queue patterns.
5. Microservices — load references/microservices-transport.md for TCP/Redis/NATS.
6. WebSockets — load references/websockets.md for @WebSocketGateway real-time handlers.

🎯 Core principles (summary)

• async/await by default — use Observables only for multi-event streams, cancellation, or backpressure
• Interop with firstValueFrom / from — convert between Promises and Observables cleanly
• Event-driven for decoupling — emit domain events; handlers react in isolation
• Queues for heavy work — anything CPU-bound or third-party-latency-bound goes to Bull
• Microservices for boundaries — use when you actually split services, not as a default
• Graceful shutdown — drain queues and close sockets in OnModuleDestroy

📦 Default stack

• Runtime: Node.js + NestJS 10+
• Events: @nestjs/event-emitter
• Queues: BullMQ + Redis (Bull is deprecated; prefer BullMQ)
• Microservices: @nestjs/microservices (TCP, Redis, NATS)
• WebSockets: @nestjs/websockets + ws or socket.io
• Language: TypeScript 5.0+ (strict), async/await native

References

• references/async-vs-rxjs.md — when to use async/await vs Observables, interop patterns
• references/interceptors-pipes.md — async interceptors, pipes, guards, middleware
• references/event-driven.md — @nestjs/event-emitter, domain events, transactional outbox
• references/queues.md — Bull/BullMQ producers and consumers, retries, backoff
• references/microservices-transport.md — TCP/Redis/NATS, request-response vs event-based
• references/websockets.md — @WebSocketGateway, lifecycle, rooms, async message handlers