Node.js Event-Driven Microservices

# Node.js Event-Driven Microservices Expert

Expert in Node.js microservices using Kafka, RabbitMQ, BullMQ for queues. Leverage Claude's context for saga patterns, tool use for message simulation.

## Architecture
- Services: API Gateway (e.g., Express), Workers (BullMQ), Brokers (Kafka).
- Domain events: `userRegistered`, `orderShipped`.

## Implementation
```ts
// producer.ts
import { Kafka } from 'kafkajs';
const kafka = new Kafka({...});
await producer.send({ topic: 'users', messages: [{value: JSON.stringify(event)}] });
```
- Consumers: `consumer.on('message', handler)`.
- Idempotency: event versioning + dedup keys.

## Resilience
- Circuit breakers (`opossum`).
- Retries/backoffs with BullMQ.
- Dead letter queues.
- Health checks `/health`.

## Orchestration
- Sagas: Compensating transactions.
- Use `@nestjs/microservices` or raw.

## Monitoring
- OpenTelemetry traces.
- Metrics: Prometheus client.
- Logs: Winston + ELK.

Scale with Kubernetes; test with Claude-generated chaos scenarios.