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https://issues.apache.org/jira/browse/KAFKA-4277?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15866415#comment-15866415
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Wrikken commented on KAFKA-4277:
--------------------------------

Reproduced on our side with Scala 2.11 kafka_2.11-0.10.1.1, zookeeper v. 3.4.5 
(3.4.5+dfsg-2+deb8u1 from Debian Jessie).

[2017-02-13 06:05:11,793] INFO re-registering broker info in ZK for broker 1 
(kafka.server.KafkaHealthcheck$SessionExpireListener)
[2017-02-13 06:05:11,795] INFO Creating /brokers/ids/1 (is it secure? false) 
(kafka.utils.ZKCheckedEphemeral)
[2017-02-13 06:05:11,797] INFO Partition [com.takeaway.events.order.create,5] 
on broker 1: Shrinking ISR for partition [com.takeaway.events.order.create,5] 
from 3,1 to 1 (kafka.cluster.Partition)
[2017-02-13 06:05:11,801] INFO Partition [__consumer_offsets,31] on broker 1: 
Shrinking ISR for partition [__consumer_offsets,31] from 3,2,1 to 2,1 
(kafka.cluster.Partition)
[2017-02-13 06:05:11,801] INFO Result of znode creation is: NODEEXISTS 
(kafka.utils.ZKCheckedEphemeral)

The more annoying issue is I can deal with Kafka fully failing at that point, 
which would prompt a restart. However, currently it 'silently' fails, but keeps 
running, forcing us to set up extra monitoring to force a restart when this 
happens.

> creating ephemeral node already exist
> -------------------------------------
>
>                 Key: KAFKA-4277
>                 URL: https://issues.apache.org/jira/browse/KAFKA-4277
>             Project: Kafka
>          Issue Type: Bug
>    Affects Versions: 0.10.0.0
>            Reporter: Feixiang Yan
>
> I use zookeeper 3.4.6.
> Zookeeper session time out, zkClient try reconnect failed. Then re-establish 
> the session and re-registering broker info in ZK, throws NODEEXISTS Exception.
>  I think it is because the ephemeral node which created by old session has 
> not removed. 
> I read the 
> [ZkUtils.scala|https://github.com/apache/kafka/blob/0.8.1/core/src/main/scala/kafka/utils/ZkUtils.scala]
>  of 0.8.1, createEphemeralPathExpectConflictHandleZKBug try create node in a 
> while loop until create success. This can solve the issue. But in 
> [ZkUtils.scala|https://github.com/apache/kafka/blob/0.10.0.1/core/src/main/scala/kafka/utils/ZkUtils.scala]
>   0.10.1 the function removed.
> {noformat}
> [2016-10-07 19:00:32,562] INFO Socket connection established to 
> 10.191.155.238/10.191.155.238:21819, initiating session 
> (org.apache.zookeeper.ClientCnxn)
> [2016-10-07 19:00:32,563] INFO zookeeper state changed (Expired) 
> (org.I0Itec.zkclient.ZkClient)
> [2016-10-07 19:00:32,564] INFO Unable to reconnect to ZooKeeper service, 
> session 0x1576b11f9b201bd has expired, closing socket connection 
> (org.apache.zookeeper.ClientCnxn)
> [2016-10-07 19:00:32,564] INFO Initiating client connection, 
> connectString=10.191.155.237:21819,10.191.155.238:21819,10.191.155.239:21819/cluster2
>  sessionTimeout=6000 watcher=org.I0Itec.zkclient.ZkClient@ae71be2 
> (org.apache.zookeeper.ZooKeeper)
> [2016-10-07 19:00:32,566] INFO Opening socket connection to server 
> 10.191.155.237/10.191.155.237:21819. Will not attempt to authenticate using 
> SASL (unknown error) (org.apache.zookeeper.ClientCnxn)
> [2016-10-07 19:00:32,566] INFO Socket connection established to 
> 10.191.155.237/10.191.155.237:21819, initiating session 
> (org.apache.zookeeper.ClientCnxn)
> [2016-10-07 19:00:32,566] INFO EventThread shut down 
> (org.apache.zookeeper.ClientCnxn)
> [2016-10-07 19:00:32,567] INFO Session establishment complete on server 
> 10.191.155.237/10.191.155.237:21819, sessionid = 0x1579ecd39c20006, 
> negotiated timeout = 6000 (org.apache.zookeeper.ClientCnxn)
> [2016-10-07 19:00:32,567] INFO zookeeper state changed (SyncConnected) 
> (org.I0Itec.zkclient.ZkClient)
> [2016-10-07 19:00:32,608] INFO re-registering broker info in ZK for broker 3 
> (kafka.server.KafkaHealthcheck$SessionExpireListener)
> [2016-10-07 19:00:32,610] INFO Creating /brokers/ids/3 (is it secure? false) 
> (kafka.utils.ZKCheckedEphemeral)
> [2016-10-07 19:00:32,611] INFO Result of znode creation is: NODEEXISTS 
> (kafka.utils.ZKCheckedEphemeral)
> [2016-10-07 19:00:32,614] ERROR Error handling event ZkEvent[New session 
> event sent to kafka.server.KafkaHealthcheck$SessionExpireListener@324f1bc] 
> (org.I0Itec.zkclient.ZkEventThread)
> java.lang.RuntimeException: A broker is already registered on the path 
> /brokers/ids/3. This probably indicates that you either have configured a 
> brokerid that is already in use, or else you have shutdown this broker and 
> restarted it faster than the zookeeper timeout so it appears to be 
> re-registering.
>         at kafka.utils.ZkUtils.registerBrokerInZk(ZkUtils.scala:305)
>         at kafka.utils.ZkUtils.registerBrokerInZk(ZkUtils.scala:291)
>         at kafka.server.KafkaHealthcheck.register(KafkaHealthcheck.scala:70)
>         at 
> kafka.server.KafkaHealthcheck$SessionExpireListener.handleNewSession(KafkaHealthcheck.scala:104)
>         at org.I0Itec.zkclient.ZkClient$6.run(ZkClient.java:735)
>         at org.I0Itec.zkclient.ZkEventThread.run(ZkEventThread.java:71)
> {noformat}



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