Job Queues Explained: Retries, Idempotency, and Dead-Letter Queues

A technical guide published on DEV Community breaks down the core challenges of designing reliable job queue systems for backend applications. The article explains three message delivery guarantees — at-most-once, at-most-once, and exactly-once — and how the choice affects data integrity and duplicate processing risks. It covers how to calculate correct visibility timeouts, write idempotent jobs using Redis or Postgres deduplication keys, and configure exponential backoff retries with dead-letter queues in BullMQ and SQS. The guide also addresses the outbox pattern to prevent double-write issues between a database and a message broker. Practical comparisons between SQS, RabbitMQ, Redis/BullMQ, and Kafka are included to help developers choose the right tool based on volume and use case.