Design an idempotent job queue that processes background tasks exactly once despite retries and crashes.
Background jobs fail, retry, and get redelivered. If a job sends an email or charges a card, running it twice is a real problem. The design combines at-least-once delivery with idempotent handlers, visibility timeouts, and dead-letter queues. Here is how to make jobs safe.
Updated Sep 2026 · Grounded in real GenAI, LLM, and AI/ML engineering interview loops and written to a senior-engineer editorial bar.
Background jobs fail, retry, and get redelivered. If a job sends an email or charges a card, running it twice is a real problem. The design combines at-least-once delivery with idempotent handlers, visibility timeouts, and dead-letter queues. Here is how to make jobs safe.
Lead with where the obvious approach breaks, because that is the judgment they are screening for — most candidates jump straight to the happy path and lose the room.
Then walk the failure back through the pipeline in order, naming the one metric the customer's exec sponsor actually cares about before you propose the fix.
