What does Apache Kafka use Zookeeper for?

Why is Zookeeper used in Kafka?

Apache Kafka uses Apache Zookeeper to store the cluster’s most important metadata - broker info, partition locations, which replica is the leader for different partitions, etc.

Zookeeper is being phased out and will not be required for Kafka in the future once Kafka’s KRaft mode is ready. Check out Kafka without Zookeeper.