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I've setup NServiceBus to forward failed messages to an error queue which is monitored by ServiceControl.

Here's my config:

 <section name="MessageForwardingInCaseOfFaultConfig" type="NServiceBus.Config.MessageForwardingInCaseOfFaultConfig, NServiceBus.Core" />
<MessageForwardingInCaseOfFaultConfig ErrorQueue="error" />

When I send a message that fails to be processed, it's sent to the DLQ. However, I can't find a copy of this message in the error or error.log queue. When I look at the message details in AMS, the Delivery Counter is set to 7, but when I check the NSB logs, I can only find the exception once. Also, I'm a bit confused as to why this exceptions is logged as "INFO". It makes it a lot harder to detect that way, but that's a seperate concern.

Note: I'm running on Azure Service Bus Transport.

Anyone an idea of what I'm missing here? Thanks in advance!

Laila
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1 Answers1

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When a handler is trying to process a message and is failing, message will become visible and will be retried again. If delivery count set on the queue is low, the message will fail processing and ASB will natively DLQ it. That's why the message ends up in the ASB DLQ and not in the NSB`s configured error queue.

The information you see on your DLQ-ed message is confirming that. The default MaxDeliveryCount in NSB.ASB v5 is set to 6, so ASB will DLQ your message the moment message is attempted to be processed more than that.

This is due to NSB having it's own (per-instance) retry counter and not using the native DeliveryCount provided by ASB. If you have your endpoint scaled out, you'll need to adjust the MaxDeliveryCount since each instance of role can grab a message and attempt to process it. Each instance will have it's retry counter. As a result of that, instance counter could be below 6, but message DeliveryCount will exceed that.

Sean Feldman
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