Javascript Azure Function Output going to Dead Letter Queue

Question

I have a javascript Azure function that puts a message on a Service Bus queue:

module.exports = function (context, req) {
  var flatten = require('flat')

  var message = flatten(req.body);
  context.bindings.outputSbMsg = message;
  context.done();
};

When it runs via a Http trigger, the function completes successfully. However, the message ends up on the Dead Letter queue in Service Bus. I can't see any error in the logs. Where should I look to investigate what the cause of this is?

Can you check the DeadLetterReason and DeadLetterErrorDescription properties on messages in the dead letter queue? Find common reasons messages are moved to the dead letter queue at docs.microsoft.com/en-us/azure/service-bus-messaging/… — Evandro Paula
That probably means there is somebody who processes those messages, and it crashes while doing so — Mikhail Shilkov
How do I examine the dead letter queue? I can't see it in the portal, or in Service Bus Explorer. — Aidan

Harsha Nalluru Harsha Nalluru · Accepted Answer · 2020-12-13T23:00:32

Messages have a deliveryCount property on them, maxDeliveryCount is settable on a queue when the queue is created or being updated.

A message in the queue can only be received as many times as the maxDeliveryCount, i.e., once the delivery-count reaches the max-delivery-count, the message can't be received using a receiver for a queue since it will be moved to the deadletter queue.

If you want to receive the message after it is moved to the deadletter queue, you need to create a receiver for the deadletter queue.

Refer to this sample processMessageFromDLQ.js which does the same with version 7.0.0 @azure/service-bus.

Moreover, you can also explicitly send messages to deadletter queue by specifying the reason, refer to the sample movingMessagesToDLQ.js

Version 7.0.0 has been recently published. Refer to the links below.

Javascript Azure Function Output going to Dead Letter Queue

1 Answers