What is ZooKeeper's role in traditional Kafka and what replaced it?

Historically, Apache ZooKeeper stored all Kafka cluster metadata: broker registration, controller election, topic configuration, partition assignments, and consumer group offsets. It was a separate distributed coordination service that Kafka depended on. KRaft (Kafka Raft) protocol, introduced in Kafka 2.8 and made production-ready in 3.3, replaces ZooKeeper entirely. KRaft stores metadata in a Kafka-native log, reduces operational complexity, enables faster controller failover (<1s vs 30s), and removes the ZooKeeper dependency.

Expected key concepts: ZooKeeper, metadata, controller election, KRaft, Kafka Raft, production-ready, controller failover, operational complexity