Published Mar 17, 2022
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ZooKeeper is used in distributed systems for service synchronization and as a naming registry. When working with Apache Kafka, ZooKeeper is primarily used to track the status of nodes in the Kafka cluster and maintain a list of Kafka topics and messages.
ZooKeeper has five primary functions. Specially, ZooKeeper is used for controller election, cluster membership, topic configuration, access control lists, and quotas.
#1. Controller Election. The controller is the broker responsible for maintaining the leader/follower relationship for all partitions. If ever a node shuts down, ZooKeeper ensures that other replicas take up the role or partition leaders replacing the partition leaders in the node that is shutting down.
#2 Cluster Membership. ZooKeeper keeps a list of all functioning brokers in the cluster.
#3 Topic Configuration. ZooKeeper maintains the configuration of all topics, including the list of existing topics, number of partitions for each topic, location of the replicas, configuration overrides for topics, preferred leader node, among other details.
#4 Access Control Lists (ACLs). ZooKeeper also maintains the ACLs for all topics. This includes who or what is allowed to read/write to the topic, list of consumer groups, members of the groups, and the most recent offset each consumer group received from each partition.
#5 Quotas. ZooKeeper accesses how much data each client is allowed to read/write.