[jira] [Created] (KAFKA-5885) NPE in ZKClient

["Dustin Cote (JIRA)" <ji...@apache.org>]

Dustin Cote created KAFKA-5885:
----------------------------------

             Summary: NPE in ZKClient
                 Key: KAFKA-5885
                 URL: https://issues.apache.org/jira/browse/KAFKA-5885
             Project: Kafka
          Issue Type: Bug
          Components: zkclient
    Affects Versions: 0.10.2.1
            Reporter: Dustin Cote


A null znode for a topic (reason how this happen isn't totally clear, but not the focus of this issue) can currently cause controller leader election to fail. When looking at the broker logging, you can see there is a NullPointerException emanating from the ZKClient:
{code}
[2017-09-11 00:00:21,441] ERROR Error while electing or becoming leader on broker 1010674 (kafka.server.ZookeeperLeaderElector)
kafka.common.KafkaException: Can't parse json string: null
        at kafka.utils.Json$.liftedTree1$1(Json.scala:40)
        at kafka.utils.Json$.parseFull(Json.scala:36)
        at kafka.utils.ZkUtils$$anonfun$getReplicaAssignmentForTopics$1.apply(ZkUtils.scala:704)
        at kafka.utils.ZkUtils$$anonfun$getReplicaAssignmentForTopics$1.apply(ZkUtils.scala:700)
        at scala.collection.mutable.ResizableArray$class.foreach(ResizableArray.scala:59)
        at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
        at kafka.utils.ZkUtils.getReplicaAssignmentForTopics(ZkUtils.scala:700)
        at kafka.controller.KafkaController.initializeControllerContext(KafkaController.scala:742)
        at kafka.controller.KafkaController.onControllerFailover(KafkaController.scala:333)
        at kafka.controller.KafkaController$$anonfun$1.apply$mcV$sp(KafkaController.scala:160)
        at kafka.server.ZookeeperLeaderElector.elect(ZookeeperLeaderElector.scala:85)
        at kafka.server.ZookeeperLeaderElector$LeaderChangeListener$$anonfun$handleDataDeleted$1.apply$mcZ$sp(ZookeeperLeaderElector.scala:154)
        at kafka.server.ZookeeperLeaderElector$LeaderChangeListener$$anonfun$handleDataDeleted$1.apply(ZookeeperLeaderElector.scala:154)
        at kafka.server.ZookeeperLeaderElector$LeaderChangeListener$$anonfun$handleDataDeleted$1.apply(ZookeeperLeaderElector.scala:154)
        at kafka.utils.CoreUtils$.inLock(CoreUtils.scala:213)
        at kafka.server.ZookeeperLeaderElector$LeaderChangeListener.handleDataDeleted(ZookeeperLeaderElector.scala:153)
        at org.I0Itec.zkclient.ZkClient$9.run(ZkClient.java:825)
        at org.I0Itec.zkclient.ZkEventThread.run(ZkEventThread.java:72)
Caused by: java.lang.NullPointerException
{code}

Regardless of how a null topic znode ended up in ZooKeeper, we can probably handle this better, at least by printing the path up to the problematic znode in the log. The way this particular problem was resolved was by using the ``kafka-topics`` command and seeing it persistently fail trying to read a particular topic with this same message. Then deleting the null znode allowed the leader election to complete.



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