Publish Events: A service publishes an event when a significant action or state?

Short answer: change occurs, such as creating a new order or processing a payment. The event is typically sent to a message broker like Kafka or RabbitMQ.

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.