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Pre-Kraft brokers currently register 0 for every controller metric. They do this because in the case of a controller failover, the metrics of a newly elected controller will no longer be 0. KRaft does not have this issue because processes with just the "broker" role are not eligible to become controllers. There is some performance overhead associated with registering metrics, so moving forward it would be best if KRaft brokers do not expose controller metrics.

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