Outbox Pattern Solves Publishing. Inbox Pattern Solves Processing.

The article explains that reliable event-driven systems need two safeguards: the Outbox Pattern for safe event publishing and the Inbox Pattern for safe event consumption.

Because brokers like Kafka and RabbitMQ usually deliver at least once, the same event can be processed more than once even after a successful publish.

It walks through failure cases and shows why simple idempotency alone is often not enough to fully protect workflows.

The Inbox Pattern adds deduplication on the consumer side to prevent duplicate payments, emails, and state changes.