KRaft controller roles in Kafka 4.0: combined versus dedicated placement after ZooKeeper removal
Apache Kafka 4.0 removes ZooKeeper mode entirely, so brokers configured with zookeeper.connect will not start. Operators migrating from an existing ZooKeeper cluster must therefore choose a KRaft controller topology before the cutover. The migration path is one-way and does not support rolling mixed-mode upgrades, which means the decision cannot be deferred
apachekafka