DLQ

Asynchronous messaging infrastructure concept, central to reliable EDI integration.

Definition

A Dead-Letter Queue (DLQ) receives messages a broker fails to deliver: expired (TTL exceeded), rejected without requeue (requeue=false), or exceeding a queue's maximum length. It isolates failures from the main flow so they can be alerted on, diagnosed and replayed manually, without blocking healthy traffic.

Origin

Formalized as an AMQP 0-9-1 protocol extension (the x-dead-letter-exchange queue argument) documented by RabbitMQ, and offered as a native primitive by Amazon SQS and Azure Service Bus in their respective documentation.

Example in context

Declaring an application queue that routes its rejects to a DLX:
queue.declare(arguments={'x-dead-letter-exchange': 'dlx', 'x-dead-letter-routing-key': 'invoices.dead'})

Related terms

• Poison message — the message that often ends up in a DLQ.
• x-death — header recording the dead-letter event.