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https://issues.apache.org/jira/browse/KAFKA-16005?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mickael Maison resolved KAFKA-16005.
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Fix Version/s: 3.7.0
Resolution: Fixed
> ZooKeeper to KRaft migration rollback missing disabling controller and
> migration configuration on brokers
> ---------------------------------------------------------------------------------------------------------
>
> Key: KAFKA-16005
> URL: https://issues.apache.org/jira/browse/KAFKA-16005
> Project: Kafka
> Issue Type: Bug
> Components: documentation
> Affects Versions: 3.6.1
> Reporter: Paolo Patierno
> Assignee: Paolo Patierno
> Priority: Major
> Fix For: 3.7.0
>
>
> I was following the latest documentation additions to try the rollback
> process of a ZK cluster migrating to KRaft, while it's still in dual-write
> mode:
> [https://github.com/apache/kafka/pull/14160/files#diff-e4e8d893dc2a4e999c96713dd5b5857203e0756860df0e70fb0cb041aa4d347bR3786]
> The first point is just about stopping broker, deleting __cluster_metadata
> folder and restarting broker.
> I think it's missing at least the following steps:
> * removing/disabling the ZooKeeper migration flag
> * removing all properties related to controllers configuration (i.e.
> controller.quorum.voters, controller.listener.names, ...)
> Without those steps, when the broker restarts, we have got broker re-creating
> the __cluster_metadata folder (because it syncs with controllers while they
> are still running).
> Also, when controllers stops, the broker starts to raise exceptions like this:
> {code:java}
> [2023-12-13 15:22:28,437] DEBUG [BrokerToControllerChannelManager id=0
> name=quorum] Connection with localhost/127.0.0.1 (channelId=1) disconnected
> (org.apache.kafka.common.network.Selector)java.net.ConnectException:
> Connection refused at
> java.base/sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) at
> java.base/sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:777)
> at
> org.apache.kafka.common.network.PlaintextTransportLayer.finishConnect(PlaintextTransportLayer.java:50)
> at
> org.apache.kafka.common.network.KafkaChannel.finishConnect(KafkaChannel.java:224)
> at
> org.apache.kafka.common.network.Selector.pollSelectionKeys(Selector.java:526)
> at org.apache.kafka.common.network.Selector.poll(Selector.java:481) at
> org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:571) at
> org.apache.kafka.server.util.InterBrokerSendThread.pollOnce(InterBrokerSendThread.java:109)
> at
> kafka.server.BrokerToControllerRequestThread.doWork(BrokerToControllerChannelManager.scala:421)
> at
> org.apache.kafka.server.util.ShutdownableThread.run(ShutdownableThread.java:130)[2023-12-13
> 15:22:28,438] INFO [BrokerToControllerChannelManager id=0 name=quorum] Node
> 1 disconnected. (org.apache.kafka.clients.NetworkClient)[2023-12-13
> 15:22:28,438] WARN [BrokerToControllerChannelManager id=0 name=quorum]
> Connection to node 1 (localhost/127.0.0.1:9093) could not be established.
> Broker may not be available. (org.apache.kafka.clients.NetworkClient) {code}
> (where I have controller locally on port 9093)
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