Broadway RabbitMQ redirect to dead-letter queue example requested

Questions / Help
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1

Hi,

I’m using BroadwayRabbitMQ.Producer to read from a RabbitMQ queue and handle the messages. However, I’m having trouble redirecting to a dead-letter queue for failed messages. In the docs it is mentioned several times, but never implemented in an example. And I simply can’t find any example on the internet as well.

I can flag the message as failed in handle_message/3 with Broadway.Message.failed/2. The message then ends up in handle_failed/2, where I want to redirect it to the dead-letter exchange/queue. There are two steps as far as I understand:

  1. ACK to the original queue
  2. Send to the dead-letter queue/exchange

I would expect to be able to reuse the existing connection to RabbitMQ to redirect to the dead-letter queue/exchange somehow.

The queues are setup as follows:

    with {:ok, queue_base} = Application.fetch_env(:amqp, :some_named_queue),
         {:ok, connection_options} = Application.fetch_env(:amqp, :connection_options),
         {:ok, conn} <- Connection.open(connection_options),
         {:ok, chan} <- Channel.open(conn),
         {:ok, _} <- Queue.declare(chan, "#{queue_base}_error", durable: true),
         # Messages that cannot be delivered to any consumer in the main queue will be routed to the error queue
         {:ok, _} <- Queue.declare(chan, queue_base,
           durable: true,
           arguments: [
             {"x-dead-letter-exchange", :longstr, ""},
             {"x-dead-letter-routing-key", :longstr, "#{queue_base}_error"}
           ]
         ),
         :ok <- Exchange.fanout(chan, "#{queue_base}_exchange", durable: true),
         :ok <- Queue.bind(chan, queue_base, "#{queue_base}_exchange") do
      :ok
    end

Thanks, Bas

2

This is probably very late, but you need to nack the message not ack
https://www.rabbitmq.com/dlx.html

3

Thanks! Better late than never :slight_smile:

So simple NACK-ing the message triggers the dead-letter queue routing. Seems quite obvious in hindsight… I try it out!

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