Pattern 14 / COMMS
Use this when letting many services react to the same business event.
Publish-Subscribe (Pub/Sub) fits when letting many services react to the same business event. Mechanism: publish an event to a topic and deliver a copy to every subscribed consumer. Use it for event-driven systems where inventory, notifications, analytics, and search all react separately. The toll: duplicates and ordering differences require idempotent subscribers.
Event-driven systems where inventory, notifications, analytics, and search all react separately.
Ordercreated fan-out to fulfillment, email, and metrics.
Describe the pressure first, then the mechanism, then the cost. That keeps the design grounded.
Same pressure family