# Dead Letter Queue

## What

* handle message failure
* A queue which other queues (source queues) can target for messages that cannot process (be consumed) successfully.

## Uses

* to set aside and isolate messages that cannot be processed correctly to determine why their processes failed
* Instead of trying to process messages that fail until they expire, move them to a dead-letter queue after a few process attempts.
  * This can reduce load on consumer/queue having to constantly retry the message, save costs if managed service
* troubleshoot incorrect message transmission operations.

### Examples

* 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

## Not to use

* to decrease the number of messages and to reduce the possibility that you expose your system to messages that you can receive but cannot process.
* with standard queues when you want to retry the transmission of a message indefinitely
* with a FIFO queue if you do not want to break the exact order of messages or operations