Week 5 Day 1: Message Queues - Decoupling Components

When User A registers, you need to:

1. Create DB entry (50ms).
2. Send Welcome Email (2000ms).
3. Update CRM (500ms).

If you do this Synchronously, user waits 2.5s. If Email Service is down, Registration fails.

Solution: Message Queues

1. User Registers -> Create DB entry (50ms).
2. Publish Event: “UserCreated” -> Queue (5ms).
3. Return “Success” to user (Total 55ms).
4. Worker Service picks up event from Queue and sends email in background.

Benefits

• Decoupling: The Email service can be down, but registration still works. Messages just pile up in the Queue until it recovers.
• Traffic Spikes: If 1M users join at once, the queue acts as a buffer. Workers consume at their own pace.

Common Technologies

• RabbitMQ: Traditional AMQP. Good for complex routing.
• Kafka: High throughput log. Good for streaming data.
• AWS SQS: Simple, managed, infinite scaling.

Tomorrow: What if multiple services need to hear the same message? Pub/Sub. 📢

Next Step

Next: Pub Sub →