RabbitMQ and round robin topic exchanges

Question

I'm seeking some advise as to how best configure my rabbitMQ exchanges.

I'm trying to use a topic exchange in a round robin methodology. Each consumer has its own (uniquely) named queue attached to a topic exchange. I would like the exchange to round robin messages to each consumer queue for the "same" topic - lets say *.log for example.

I have tried multiple combinations and only seem to be able to simultaneously deliver messages to the consumer queues which effectively means I'm processing the message twice, once in each consumer.

For clarity I also have a fanout exchange, which I use to "control" the consumers (start, stop etc).this should remain in place in any outcome.

Any guidance on how best to achieve the stated outcome would be great.

Answer 1

Each consumer has its own (uniquely) named queue attached to a topic exchange

The trick is to have every worker/consumer that you want to round-robin between to setup a named queue and all use the same queue instead creating their own.

So you could create a named queue called "log" for all of the "log" workers. You would create a different named queue for say "foo" for all of the "foo" workers. Requests will be delivered round-robin to all consumers looking at the same queue.

Answer 2

To use RabbitMQ in round robin fashion, better to use direct exchange instead of topic exchange.

A direct exchange is ideal for the unicast routing of messages (although they can be used for multicast routing as well).

• A queue binds to the exchange with a routing key K.
• When a new message with routing key R arrives at the direct exchange, the exchange routes it to the queue if K = R.

Direct exchanges are often used to distribute tasks between multiple workers in a round robin manner. When doing so, it is important to understand that, messages are load balanced between consumers and not between queues.