Trouble with RabbitMQ fanout exchange

Question

I am able to create a fanout exchange using the Publish/Subscribe RabbitMQ Java tutorial, and any connected consumer will receive a copy of a message. Instead of declaring an exchange and binding dynamically/programmatically, I would like to create the exchange and the binding prior to connecting any consumers. I have done this through the RabbitMQ Management Console. For some reason, however, my consumers are receiving messages in a round-robin fashion, rather than all receiving copies of the message. What am I missing? Here are some code snippets:

Publisher:

channel.basicPublish("public", "", null, rowId.getBytes("UTF-8"));

Consumer:

QueueingConsumer consumer = new QueueingConsumer(channel);
            channel.basicConsume("myqueue", false, consumer);

...And in the RabbitMQ Management console, I created an exchange "public" of type "fanout", and I set a binding from that exchange to "myqueue".

I'd appreciate any help!

Answer 1

It sounds like all of your consumers are subscribing to the same queue. When multiple consumers are subscribing to the same queue, the default behavior of RabbitMQ is to round-robin the messages between all the subscribed consumers. See "Round-robin dispatching" in the RabbitMQ Tutorial #2: Work Queues.

The fanout exchange is for ensuring that each queue bound to it gets a copy of the message, not each consumer. If you want each consumer to get a copy of the message, typically you would have each consumer create their own queue and then bind to the exchange. I'm not sure why you're trying to avoid programmatically creating/binding a queue, but if you know ahead of time the number of subscribers and create a queue for each one, you can get the same effect.