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https://issues.apache.org/jira/browse/KAFKA-7974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16786494#comment-16786494
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ASF GitHub Bot commented on KAFKA-7974:
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cmccabe commented on pull request #6305: Fix for KAFKA-7974: Avoid zombie
AdminClient when node host isn't resolvable
URL: https://github.com/apache/kafka/pull/6305
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> KafkaAdminClient loses worker thread/enters zombie state when initial DNS
> lookup fails
> --------------------------------------------------------------------------------------
>
> Key: KAFKA-7974
> URL: https://issues.apache.org/jira/browse/KAFKA-7974
> Project: Kafka
> Issue Type: Bug
> Reporter: Nicholas Parker
> Priority: Major
>
> Version: kafka-clients-2.1.0
> I have some code that creates creates a KafkaAdminClient instance and then
> invokes listTopics(). I was seeing the following stacktrace in the logs,
> after which the KafkaAdminClient instance became unresponsive:
> {code:java}
> ERROR [kafka-admin-client-thread | adminclient-1] 2019-02-18 01:00:45,597
> KafkaThread.java:51 - Uncaught exception in thread 'kafka-admin-client-thread
> | adminclient-1':
> java.lang.IllegalStateException: No entry found for connection 0
> at
> org.apache.kafka.clients.ClusterConnectionStates.nodeState(ClusterConnectionStates.java:330)
> at
> org.apache.kafka.clients.ClusterConnectionStates.disconnected(ClusterConnectionStates.java:134)
> at
> org.apache.kafka.clients.NetworkClient.initiateConnect(NetworkClient.java:921)
> at org.apache.kafka.clients.NetworkClient.ready(NetworkClient.java:287)
> at
> org.apache.kafka.clients.admin.KafkaAdminClient$AdminClientRunnable.sendEligibleCalls(KafkaAdminClient.java:898)
> at
> org.apache.kafka.clients.admin.KafkaAdminClient$AdminClientRunnable.run(KafkaAdminClient.java:1113)
> at java.lang.Thread.run(Thread.java:748){code}
> From looking at the code I was able to trace down a possible cause:
> * NetworkClient.ready() invokes this.initiateConnect() as seen in the above
> stacktrace
> * NetworkClient.initiateConnect() invokes
> ClusterConnectionStates.connecting(), which internally invokes
> ClientUtils.resolve() to to resolve the host when creating an entry for the
> connection.
> * If this host lookup fails, a UnknownHostException can be thrown back to
> NetworkClient.initiateConnect() and the connection entry is not created in
> ClusterConnectionStates. This exception doesn't get logged so this is a guess
> on my part.
> * NetworkClient.initiateConnect() catches the exception and attempts to call
> ClusterConnectionStates.disconnected(), which throws an IllegalStateException
> because no entry had yet been created due to the lookup failure.
> * This IllegalStateException ends up killing the worker thread and
> KafkaAdminClient gets stuck, never returning from listTopics().
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