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This KIP introduces one new broker-side extension interface and one new broker configuration.

New Interface

/**
 * A callback interface that users can implement to get notified when a consumer group rebalance occurs.
 * <p>
 * This listener is invoked on the broker side (GroupCoordinator) when a consumer group's epoch is bumped,
 * which indicates that a rebalance has occurred. 
 * <p>
 * Implementations of this interface can be used for monitoring, alerting, or logging purposes
 * to track which consumer groups are experiencing rebalances.
 */
public interface ConsumerGroupRebalanceListener {

    /**
     * Called when a consumer group rebalance occurs.
     *
     * @param groupId The ID of the consumer group that rebalanced
     * @param groupEpochgroupType The newtype of group epoch after the rebalancethat rebalanced
     * @param metadataHashreason The rebalance reason
     * @param eventTimeMs The event timestamp in milliseconds metadata hash of the group after the rebalance
     */
    void onConsumerGroupRebalance(String groupId, String groupType, intString groupEpochreason, long metadataHasheventTimeMs);
}

New Broker Configuration

group.consumer.rebalance.listener.classes (LIST, default: empty)

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