A mix of Topology 1 and Topology 2:

In this topology, we have some producers/consumers that are local to a given cluster while others can produce/consume to any cluster.

The benefit of this topology is that applications can choose to produce/consume locally to their cluster and let the cluster-level load-balancer balance the load between nodes OR they can choose to produce/consume from the federation-level load-balancer.

When using load-balancer with RabbitMQ, the nodes act as servers and the Producers and Consumers are the customers. It is depicted in the following diagram.

The applications only know about the load-balancer IP. The load-balancer will transparently connect them to the cluster node with the lowest connection load.

HA Proxy within the Data Bus will also act as an SSL/TLS offloading solution. All the connections from the Producers and consumers, up until HAProxy, will be over TLS. HAProxy will then be responsible for converting an SSL/TLS event message to simple AMQP event message and transferring it to the underlying software: