NestJS microservices module

NestJS microservices use transport layers (TCP, Redis, NATS, Kafka, gRPC, MQTT) alongside or instead of HTTP. `@MessagePattern` and `@EventPattern` bind handlers to message shapes.

					@Controller()
export class OrdersMsController {
  @MessagePattern({ cmd: 'get_order' })
  getOrder(@Payload() data: { id: string }) {
    return this.orders.findOne(data.id);
  }

  @EventPattern('order_created')
  onOrderCreated(@Payload() event: OrderCreatedEvent) {
    return this.notifications.send(event);
  }
}
				

Hybrid apps connect HTTP and microservice transports in one process. Serialization, timeouts, retries, and dead-letter handling are transport-specific. Idempotency matters for at-least-once delivery.

On interviews: when to split HTTP and messaging boundaries, request-response versus fire-and-forget events, and health checks across transports.

Common pitfalls: treating message handlers like HTTP without timeout/retry policy, shared mutable state between transports, and missing correlation IDs across services.

The trade-off is balancing simplicity, performance, safety, and operability — name which axis you optimized and what cost you accepted.

Checklist:

• Choose transport by delivery and ops requirements.
• Define explicit message contracts and versioning.
• Implement timeouts, retries, and idempotency.
• Keep domain logic transport-agnostic in services.