From Synchronous to Asynchronous — A Practical Guide to Migrating Commerce APIs to Message Queues, Outbox, and Workflow Engines

Replace synchronous coupon issuance and product registration APIs that buckle under sale-launch traffic with a queue, outbox, idempotent consumer, DLQ, and Temporal—and reproduce the before-and-after metrics (latency, failure rate, and DB commits) under the same load on my computer using Docker.