Message Queue — Async Processing

Async processing utilizes message queues like RabbitMQ, AWS SQS, Kafka, or Redis Streams to move heavy tasks out of the request path, preventing high p99 latency and thread pool timeouts. Meanwhile, async route handling differs between frameworks. Express 4 fails to catch Promise rejections in its synchronous try/catch block, leading to unhandledRejection and process crashes. Conversely, Fastify uses pipeline hooks to await handlers, ensuring rejections are captured and passed to the setErrorHandler for proper management.