RabbitMQ - 如何配置条件 DLX？

Question

I have active queue which will have all messages from Publisher. My Consumer reads those message and Acks/Nacks depending on the message processing result.

while (true)
{
   var ea = (BasicDeliverEventArgs)consumer.Queue.Dequeue();

   var body = ea.Body;
   var message = Encoding.UTF8.GetString(body);

   var processed = ProcessMessage(message)

   if (processed)                        
      channel.BasicAck(deliveryTag: ea.DeliveryTag, multiple: false);
   else
      channel.BasicNack(deliveryTag: ea.DeliveryTag, multiple: false, requeue: true);
}

My questions are

• Is setting true for requeue parameter when it is nacked correct?
• Or do we need to create another queue for Retry?
• Let us say, if I want to move the message to DLX after retrying for 10 times? How do I do it? Is it C# code or can a rule be defined on the queue?
• How do I know that a message is retried for 10 times? Does RabbitMQ provide any mechanism or do I need to manually design message object to contain retry count?

Thanks for your inputs

Answer 1

Starting with release 3.5.2, RabbitMQ automatically adds a header to dead-letterred messages with informations such as:

• the queue(s) which saw the message
• the reason(s) it was dead-letterred
• the number of times it was dead-letterred
• timestamps

Look at the "Dead-Lettered Messages" section near the end of the DLX documentation for more details.

If you use an older version of RabbitMQ, then @Franklin's solution should work.

Answer 2

if you set requeue to false then it will go to any DeadLetter Exchange assigned to the Queue. True will requeue the message.

What I have done for retry attempts is to Create a Hold Exchange and Queue. If you want to retry a message Return a positive Ack to the Queue, Add a RetryAttepmts Header to the Message then Publish it to the HoldQueue Exchange with a timeout value. Set the Hold Queue Dead Letter Exchange to an exchange that will send the message to the original Queue. Then Check the header and nack if the retry attempts are too large.