This KIP defines the behavior and set of new APIs for the “bridge release” as first mentioned in KIP-500.

Public Interfaces

Metrics

MBean name	Description
kafka.server:type=KafkaServer,name=MetadataType	An enumeration of: ZooKeeper (1), Dual (2), KRaft (3). Each broker reports this.
kafka.controller:type=KafkaController,name=Features,feature={feature},level={

leve

level}	The finalized set of features with their level as seen by the controller. Used to help operators see the cluster's current metadata.version
kafka.controller:type=KafkaController,name=MigrationState	An enumeration of the possible migration states the cluster can be in. This is only reported by the active controller. The "ZooKeeper" and "MigrationEligible" states are reported by the ZK controller, while the remaining states are reported by the KRaft controller.
kafka.controller:type=KafkaController,name=ZooKeeperWriteBehindLag	The amount of lag in records that ZooKeeper is behind relative to the highest committed record in the metadata log. This metric will only be reported by the active KRaft controller.

A new metadata.version will be used for a few things in this design.

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