Dead Letter Channel

Dead Letter Channel

Camel supports the Dead Letter Channel from the EIP patterns using the DeadLetterChannel processor which is an Error Handler.

Redelivery

It is common for a temporary outage or database deadlock to cause a message to fail to process; but the chances are if its tried a few more times with some time delay then it will complete fine. So we typically wish to use some kind of redelivery policy to decide how many times to try redeliver a message and how long to wait before redelivery attempts.

The RedeliveryPolicy defines how the message is to be redelivered. You can customize things like

• how many times a message is attempted to be redelivered before it is considered a failure and sent to the dead letter channel
• the initial redelivery timeout
• whether or not exponential backoff is used (i.e. the time between retries increases using a backoff multiplier)
• whether to use collision avoidence to add some randomness to the timings

Once all attempts at redelivering the message fails then the message is forwarded to the dead letter queue.

Redelivery header

When a message is redelivered the DeadLetterChannel will append a customizable header to the message to indicate how many times its been redelivered. The default value is org.apache.camel.redeliveryCount.