Two or more clusters of RabbitMQ with a pair of federated exchanges:

In this arrangement, each exchange links to the other and is symmetric in nature. Consumers in Cluster B can receive messages published by producers in Cluster A. Similarly, consumers in Cluster A can receive messages published by producers in Cluster B. The downside is that if Cluster A goes down, publishers for cluster A can no longer publish messages.

Please note that there would be a single Load Balancer shared by both producers and consumers.