How do you scale RabbitMQ horizontally?

Scaling RabbitMQ horizontally is less about "adding more nodes" alone and more about spreading load across queues, nodes, and even clusters in a deliberate way.

1. Shard busy topics across multiple queues using a consistent-hash exchange, so a single hot queue doesn't become the bottleneck.
2. Add cluster nodes and place quorum queue replicas across them, so both throughput capacity and fault tolerance grow together.
3. Use federation to link exchanges/queues between geographically distant clusters, keeping most traffic local while still sharing relevant events across regions.
4. Use the shovel plugin for simpler, one-directional bulk movement of messages between clusters, such as migrating a workload.
5. Scale consumers independently of nodes - since queue throughput is bounded by consumer processing speed, adding consumer instances is often the cheapest scaling lever.

It is worth noting that adding cluster nodes does not automatically parallelize a single classic queue - a classic queue's messages still live on one node, so true horizontal scaling comes from spreading work across multiple queues and consumers, not just multiple nodes.