[GitHub] [kafka] rondagostino commented on pull request #11133: KAFKA-13140: KRaft brokers do not expose kafka.controller metrics

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rondagostino commented on pull request #11133:
URL: https://github.com/apache/kafka/pull/11133#issuecomment-904022863


   > I am not sure we should expose controller metrics for brokers that don't have the controller role.
   
   I agree it is a bit counter-intuitive.  Now that you bring up this hesitance, here is how I see it.
   
   It *may* make sense from a backwards-compatibility perspective: those metrics are there on non-controllers today with values equal to 0, so it could be argued that for compatibility purposes they should be there for non-controller KRaft nodes.
   
   That being said, though, the reason the controller metrics are available on ZK-based brokers today is because those brokers may soon be elected as the controller -- they are "controller-eligible".  A KRaft node that has `process.roles=broker` is not controller-eligible, so that's an argument against exposing the controller metrics on KRaft broker nodes.  Similarly, today we expose broker metrics on a node that is the (ZK-based) controller because that node **is** also a broker.  A KRaft node with `process.roles=controller` does not currently expose broker metrics -- we have not made any such backwards-compatibility argument for this case and probably would not do so given the volume of metrics and the fact that the node it is not broker-eligible.
   


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