Building an Idempotent Job Queue in Node. js That Never Runs the Same Task Twice

Today, in modern backends, you probably have those distributed job queues for everything, including sending emails, processing payments, generating reports, and syncing data to third parties. As soon as you add retries to handle transient failures, however, you inherit a hard problem: how do you ensure that when the network, worker, or broker can fail at any point, your job runs exactly once?

The short answer is: "exactly once delivery" is a great concept, but in practice it's mostly fiction given the nature of distributed systems. What you really can make is at-least-once delivery + idempotent processing, yielding exactly once effects. This article demonstrates how to accomplish this in Node.js with a tangible, functioning implementation.