Idempotency Beyond API (Application Programming Interface) Requests: A Layered Defense
Idempotency isn't one header. It's a defense stack that has to be built separately across five layers, from the API key down to the step marker.
Messaging Articles
Posts about messaging
The Outbox/Inbox Pattern in Payment Systems
If a database write and an event publish aren't in the same transaction, one can vanish or duplicate. Outbox publishes; inbox dedups on the consumer.
Effectively-Once Processing in Payments
Exactly-once messaging is a lie. How defense in depth — idempotency, dedup, outbox, and reconciliation — produces an effectively-once business outcome.