[jira] [Created] (FLINK-7340) Taskmanager hung after temporary DNS outage

["Joshua Griffith (JIRA)" <ji...@apache.org>]

Joshua Griffith created FLINK-7340:
--------------------------------------

             Summary: Taskmanager hung after temporary DNS outage
                 Key: FLINK-7340
                 URL: https://issues.apache.org/jira/browse/FLINK-7340
             Project: Flink
          Issue Type: Bug
          Components: Core
    Affects Versions: 1.3.1
         Environment: Non-HA Flink running in Kubernetes.
            Reporter: Joshua Griffith


After a Kubernetes node failure, several TaskManagers and the DNS system were automatically restarted. One TaskManager was unable to connect to the JobManager and continually logged the following errors:

{quote}
2017-08-01 18:58:06.707 [flink-akka.actor.default-dispatcher-823] INFO  org.apache.flink.runtime.taskmanager.TaskManager  - Trying to register at JobManager akka.tcp://flink@jobmanager:6123/user/jobmanager (attempt 595, timeout: 30000 milliseconds)
2017-08-01 18:58:06.713 [flink-akka.actor.default-dispatcher-834] INFO  Remoting flink-akka.remote.default-remote-dispatcher-240 - Quarantined address [akka.tcp://flink@jobmanager:6123] is still unreachable or has not been restarted. Keeping it quarantined.
{quote}

After exec'ing into the container, I was able to {{telnet jobmanager 6123}} successfully and {{dig jobmanager}} showed the correct IP in DNS. I suspect that the TaskManager cached a bad IP address for the JobManager when the DNS system was restarting and it used that cached address rather than respecting the 30s TTL and getting a new one for the next request. It may be a good idea for the TaskManager to explicitly perform a DNS lookup after JobManager connection failures.



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