I see a lot of messages in flink log like below. What's the cause?
02 Apr 2018 04:09:13,554 ERROR org.apache.kafka.clients.producer.internals.Sender - Uncaught error in kafka producer I/O thread: org.apache.kafka.common.KafkaException: Error registering mbean kafka.producer:type=producer-node-metrics,client-id=producer-1,node-id=node-1 at org.apache.kafka.common.metrics.JmxReporter.reregister(JmxReporter.java:163) at org.apache.kafka.common.metrics.JmxReporter.metricChange(JmxReporter.java:81) at org.apache.kafka.common.metrics.Metrics.registerMetric(Metrics.java:504) at org.apache.kafka.common.metrics.Sensor.add(Sensor.java:255) at org.apache.kafka.common.metrics.Sensor.add(Sensor.java:240) at org.apache.kafka.common.network.Selector$SelectorMetrics.maybeRegisterConnectionMetrics(Selector.java:811) at org.apache.kafka.common.network.Selector.pollSelectionKeys(Selector.java:353) at org.apache.kafka.common.network.Selector.poll(Selector.java:326) at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:433) at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:224) at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:162) at java.lang.Thread.run(Thread.java:748) Caused by: javax.management.InstanceAlreadyExistsException: kafka.producer:type=producer-node-metrics,client-id=producer-1,node-id=node-1 at com.sun.jmx.mbeanserver.Repository.addMBean(Repository.java:437) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerWithRepository(DefaultMBeanServerInterceptor.java:1898) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerDynamicMBean(DefaultMBeanServerInterceptor.java:966) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerObject(DefaultMBeanServerInterceptor.java:900) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.registerMBean(DefaultMBeanServerInterceptor.java:324) at com.sun.jmx.mbeanserver.JmxMBeanServer.registerMBean(JmxMBeanServer.java:522) at org.apache.kafka.common.metrics.JmxReporter.reregister(JmxReporter.java:161) ... 11 more 02 Apr 2018 04:09:13,673 ERROR org.apache.kafka.common.utils.KafkaThread - Uncaught exception in kafka-producer-network-thread | producer-3: java.lang.NoClassDefFoundError: org/apache/kafka/clients/NetworkClient$1 at org.apache.kafka.clients.NetworkClient.processDisconnection(NetworkClient.java:583) at org.apache.kafka.clients.NetworkClient.handleDisconnections(NetworkClient.java:705) at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:443) at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:224) at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:162) at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.ClassNotFoundException: org.apache.kafka.clients.NetworkClient$1 at java.net.URLClassLoader.findClass(URLClassLoader.java:381) at java.lang.ClassLoader.loadClass(ClassLoader.java:424) at org.apache.flink.runtime.execution.librarycache.FlinkUserCodeClassLoaders$ChildFirstClassLoader.loadClass(FlinkUserCodeClassLoaders.java:128) at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ... 6 more Thank you, Alex