Event Bus and Message Brokers

In a choreography saga, services communicate by exchanging events. For this to work reliably in a distributed system, we need robust communication mechanisms.

Imagine an order being created, then needing payment, and finally shipping. Each step is an event triggering the next service.

• Order Service publishes OrderCreated
• Payment Service subscribes to OrderCreated, publishes PaymentProcessed
• Shipping Service subscribes to PaymentProcessed, publishes ShipmentScheduled

An Event Bus is a pattern that enables different parts of an application (or different services) to communicate by sending and receiving events without knowing about each other directly.

Think of it as a central hub where events are broadcast. Any interested party can 'listen' for specific events.

It decouples services, meaning they don't need to know who will process their events, only that an event occurred.