Apache Kafka uses Zookeeper to store metadata about the Kafka cluster, as well as consumer client details,
- ensemble: Zookeeper is designed to work as a cluster, called an ensemble, to ensure high availability. => It is recommended that ensembles contain an odd number of servers. (Recommended: 5) => With 5, 2 nodes can go down. 1 maintenance, and 1 fatal. Higher introduces latency without observers => Observer nodes for help in balancing read-only traffic.