If you are running an event-driven architecture with message queues like Kafka, you already know the drill, scalability is awesome, but network partitions, out-of-order delivery, and duplicate messages come with the territory.
Our team recently learned this the hard way during a production overhaul. A flood of duplicate webhooks bypassed our application level checks, creating a nasty race condition that left our database in an inconsistent state.
Most enterprise message brokers guarantee at-least-once delivery. That means your consumers will get duplicates eventually. If you are dealing with critical operations—like tracking payments or updating inventory processing a duplicate event will absolutely corrupt your data state.
The Breakdown: When validations fail concurrently
Our issue was a subtle concurrent execution race condition. Two identical update events hit our API nodes just milliseconds apart.
