Dead-Letter Queue

A dead-letter queue (DLQ) is where a message goes after it fails processing too many times. Instead of retrying forever and blocking the main queue, the system moves the “poison” message aside for later inspection.

Worked example: a malformed order message that throws on every attempt is routed to the DLQ after, say, five tries; the main pipeline keeps flowing while an engineer inspects the DLQ to find the bug. Gotcha: a DLQ is a symptom store, not a fix — it needs monitoring and alerting or failures pile up silently, and reprocessing DLQ messages after a fix requires care to avoid re-triggering the same failure.