How load balancer works in RabbitMQ

Question

I am new to RabbitMQ, so please excuse me for trivial questions:

1) In case of clustering in RabbitMQ, if a node fails, load shift to another node (without stopping the other nodes). Similarly, we can also add new fresh nodes to the existing cluster without stopping existing nodes in cluster. Is that correct?

2) Assume that we start with a single rabbitMQ node, and create 100 queues on it. Now producers started sending message at faster rate. To handle this load, we add more nodes and make a cluster. But queues exist on first node only. How does load balanced among nodes now? And if we need to add more queues, on which node we should add them? Or can we add them using load balancer.

Thanks In Advance

Answer 1

1) In case of clustering in RabbitMQ, if a node fails, load shift to another node (without stopping the other nodes). Similarly, we can also add new fresh nodes to the existing cluster without stopping existing nodes in cluster. Is that correct?

If a node on which the queue was created fails, rabbitmq will elect a new master for that queue in the cluster as long as mirroring for the queue is enabled. Clustering provides HA based on a policy that you can define.

2) Assume that we start with a single rabbitMQ node, and create 100 queues on it. Now producers started sending message at faster rate. To handle this load, we add more nodes and make a cluster. But queues exist on first node only. How does load balanced among nodes now?

The load is not balanced. The distributed cluster provides HA and not load balancing. Your requests will be redirected to the node in the cluster on which the queue resides.

And if we need to add more queues, on which node we should add them? Or can we add them using load balancer.

That depends on your use case. Some folks use a round robin and create queues on separate nodes.

In summary

• For HA use mirroring in the cluster.
• To balance load across nodes, use a LB to distribute across Queues.
• If you'd like to load balance the queue itself take a look at Federated Queues. They allow you to fetch messages on a downstream queue from an upstream queue.