Message Broker: Use a message broker (e.g., Kafka, RabbitMQ) to route events?

Short answer: between producers and consumers, ensuring that services are loosely coupled. Example: In an e-commerce platform, when a Payment Service publishes a PaymentSucceeded event to Kafka, the Shipping Service can subscribe to this event and initiate the shipment process asynchronously.

Real-world example (ShopNest)

After payment succeeds, ShopNest publishes OrderPaid. Inventory and Notification services react independently—no giant distributed transaction.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.