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Kafka, mail # dev - zkclient dies after UnknownHostException in zk reconnect


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Anatoly Fayngelerin 2013-09-23, 14:02
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Neha Narkhede 2013-09-24, 03:44
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Joel Koshy 2013-09-24, 07:32
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Anatoly Fayngelerin 2013-09-24, 15:28
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Neha Narkhede 2013-09-24, 15:34
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Re: zkclient dies after UnknownHostException in zk reconnect
Anatoly Fayngelerin 2013-09-24, 16:59
That does sound like a saner solution. Which github repo do you submit
patches to? It looks like the repo I posted on originally(
https://github.com/sgroschupf/zkclient/issues/23) might be a little stale.
On Tue, Sep 24, 2013 at 11:34 AM, Neha Narkhede <[EMAIL PROTECTED]>wrote:

> Thanks for explaining the bug. This is a serious issue that we should fix
> at the zkclient level. We have submitted patches to them before and they
> were pretty helpful in releasing a new version with the patch. I think that
> will lead to a cleaner solution than trying to get around it in Kafka code
> since zkclient usage is pretty wide spread across the server and consumer
> code today.
>
> Thanks,
> Neha
>
>
> On Tue, Sep 24, 2013 at 8:28 AM, Anatoly Fayngelerin <[EMAIL PROTECTED]
> >wrote:
>
> > Joel - that is exactly right. ZkClient has no way to notify consumers of
> > this situation. The session end event gets fired, however, the session
> > begin event never occurs.
> >
> > Neha - The issue manifested itself when producers were attempting to
> > discover topics/brokers. The kafka brokers had lost their ZK sessions
> > during a network outage. The outage was long enough for ZooKeeper to
> expire
> > the sessions corresponding to the ephemeral nodes in /broker/. The
> zkclient
> > bug prevented the broker from ever re-establishing the ZK session.
> > Subsequently, no zookeeper based producer was able to discover
> > topic->broker mappings. The resulting exceptions looked like:
> >
> > Caused by: kafka.common.NoBrokersForPartitionException: Partition = null
> > at
> >
> >
> kafka.producer.Producer.kafka$producer$Producer$getPartitionListForTopic(Producer.scala:167)
> > at kafka.producer.Producer$anonfun$3.apply(Producer.scala:116)
> > at kafka.producer.Producer$anonfun$3.apply(Producer.scala:105)
> > at
> >
> >
> scala.collection.TraversableLike$anonfun$map$1.apply(TraversableLike.scala:233)
> > at
> >
> >
> scala.collection.TraversableLike$anonfun$map$1.apply(TraversableLike.scala:233)
> > at
> >
> >
> scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:34)
> > at scala.collection.mutable.WrappedArray.foreach(WrappedArray.scala:33)
> > at scala.collection.TraversableLike$class.map(TraversableLike.scala:233)
> > at scala.collection.mutable.WrappedArray.map(WrappedArray.scala:33)
> > at kafka.producer.Producer.zkSend(Producer.scala:105)
> > at kafka.producer.Producer.send(Producer.scala:99)
> > at
> >
> >
> com.yieldmo.common.protobuf.ProtoKafkaWriter$class.write(ProtoKafka.scala:20)
> > at com.yieldmo.common.protobuf.ProtoWriter.write(ProtoKafka.scala:40)
> > at
> >
> >
> com.yieldmo.storm.bolt.KafkaProtoWriterBolt.execute(KafkaProtoWriterBolt.scala:48)
> >
> > As far as I can see, the only way to deal with this without patching
> > zkclient is to periodically check the status of the zk connection and try
> > to detect this kind of situation. I would love to hear better ideas for
> how
> > to handle this.
> >
> >
> > On Tue, Sep 24, 2013 at 3:31 AM, Joel Koshy <[EMAIL PROTECTED]> wrote:
> >
> > > > node loss. Did the Kafka consumer not respond to rebalance events or
> > did
> > > > the server not respond to state change events ? Also, ephemeral nodes
> > are
> > > > lost only when sessions are expired on the zookeeper server or if
> > clients
> > > > close the session actively, how does losing connection lead to
> > ephemeral
> > > > node loss?
> > >
> > > My understanding of Anatoly's observation is that on session
> > > expiration, zkclient will reconnect
> > > (
> > >
> >
> https://github.com/sgroschupf/zkclient/blob/master/src/main/java/org/I0Itec/zkclient/ZkClient.java#L458
> > > )
> > > but if the connect causes an IOException, that would effectively mean
> > > that the session will not get re-established. Anatoly, can you
> > > confirm?
> > >
> > > > On Mon, Sep 23, 2013 at 7:02 AM, Anatoly Fayngelerin <
> > [EMAIL PROTECTED]
> > > >wrote:
> > > >
> > > >> Hi Everyone,
> > > >>
> > > >> I've run into the following issue with the Kafka server. The

 
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Neha Narkhede 2013-09-24, 17:47
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Anatoly Fayngelerin 2013-09-24, 21:03