Is it advisable to add more brokers to kafka cluster although the load is still low

Question

although we do not have any perfomance issues yet, and the nodes are pretty much idle, is it advisable to increase the number of kafka brokers (and zookeepers) from 3 to 5 immediately to improve cluster high availability? The intention is then of course to increase the replication factor from 3 to 5 as a default config for critical topics.

Answer 1

If high level of data replication is essential for your business, it is advisable to increase the count of brokers. To attain this, on top of extra nodes, you are creating a technical debt on network load also. Obviously if you increase the number of brokers in cluster, you are decreasing the risk related to loosing high availability.

Answer 2

Depending of your needs. If you do not have to ensure a very high availability(example a bank), the increase of replication factor in your cluster will reducer the overall performance because when you write a message on a topic/partition, that message will be replicated in 5 nodes instead of 3. You can increase the number of nodes for high availability and distribute less partitions on every node, but without a increase of replication factor.