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The main task of a dead-letter queue is handling message failure. A dead-letter queue lets you set aside and isolate messages that can’t be processed correctly to determine why their processing didn’t succeed. Setting up a dead-letter queue allows you to do the following:
- Configure an alarm for any messages delivered to a dead-letter queue.
- Examine logs for exceptions that might have caused messages to be delivered to a dead-letter queue.
- Analyze the contents of messages delivered to a dead-letter queue to diagnose software or the producer’s or consumer’s hardware issues.
- Determine whether you have given your consumer sufficient time to process messages.
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In message queueing the dead letter queue is a service implementation to store messages that meet one or more of the following criteria:
- Message that is sent to a queue that does not exist.
- Queue length limit exceeded.
- Message length limit exceeded.
- Message is rejected by another queue exchange.
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Do use dead-letter queues with standard queues. You should always take advantage of dead-letter queues when your applications don’t depend on ordering. Dead-letter queues can help you troubleshoot incorrect message transmission operations.
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Do use dead-letter queues to decrease the number of messages and to reduce the possibility of exposing your system to poison-pill messages (messages that can be received but can’t be processed).
