[jira] [Created] (KAFKA-7974) KafkaAdminClient loses worker thread/enters zombie state when initial DNS lookup fails

["Nicholas Parker (JIRA)" <ji...@apache.org>]

Nicholas Parker created KAFKA-7974:
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             Summary: 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


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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