How pub/sub works

Publish an order event once and follow independent copies to billing, email and analytics. Take one subscriber offline without stopping the others.

When to use it

Let several services react independently to the same business event without the publisher calling each service directly.

Explore the tradeoffs

Publication and delivery counts measure different things. Independent subscribers increase delivery work and operational state.

One subscriber's filter does not remove the event from other subscriptions. Filters reduce unwanted deliveries but need deliberate schema and routing contracts.

Retaining events prevents offline misses; idempotency prevents repeated effects. Durable subscriptions need bounded retention and consumers that can catch up.

Model boundaries

One reliable broker and three existing subscriptions. Durable subscriptions retain offline deliveries without expiry in this short run. A lost acknowledgement is retried once. Idempotency models an atomic effect plus processed-event record; no global ordering or exactly-once guarantee is implied.