Cruise Control currently relies on the internal and now deprecated KafkaZkClient methods for preforming replica reassignment. With the changes made in KIP-455 in Kafka 2.4.0, CC should now be able to safely transition to use the public AdminClient methods for replica reassignment.

This transition will need to happen ASAP since:

• The KafkaZkClient methods used have been deprecated and are to be removed in a future release, which would completely cripple Cruise Control
• There have already been some related changes in Kafka 2.4 that are causing users to experience rebalancing problems, such as jobs getting stuck [1] [2].

There has been some preliminary work[3] to make these changes but they have been dragging on for several months and don't address all of the new changes with Kafka 2.4. We will likely need to drive this to make sure it gets updated/merged in a timely fashion before next release.

[1] https://github.com/linkedin/cruise-control/issues/1167#issuecomment-620314334
[2] https://issues.apache.org/jira/browse/KAFKA-9478
[3] https://github.com/linkedin/cruise-control/pull/924