Consumer is not subscribed to any topics

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产生该问题的原因主要是zookeeper中存在旧版本的kafka-connect topic信息，导致新版本的kafka-connect启动异常：

ERROR Unexpected exception in Thread[KafkaBasedLog Work Thread - connect-configs,5,main] (org.apache.kafka.connect.util.KafkaBasedLog:334)
java.lang.IllegalStateException: Consumer is not subscribed to any topics or assigned any partitions
 at org.apache.kafka.clients.consumer.KafkaConsumer.poll(KafkaConsumer.java:1109)
 at org.apache.kafka.connect.util.KafkaBasedLog.poll(KafkaBasedLog.java:256)
 at org.apache.kafka.connect.util.KafkaBasedLog.access$500(KafkaBasedLog.java:69)
 at org.apache.kafka.connect.util.KafkaBasedLog$WorkThread.run(KafkaBasedLog.java:327)

解决办法：

（1） 使用kafka命令列出所有与connect相关的topic：

bin/kafka-topics.sh --list --zookeeper 10.255.8.102:2181

输出：

__consumer_offsets
ambari_kafka_service_check
connect-configs
connect-offsets
connect-status

（2）使用kafka命令删除所有与connect相关的topic：

bin/kafka-topics.sh --delete --zookeeper 10.255.8.102:2181 --topic connect-configs
bin/kafka-topics.sh --delete --zookeeper 10.255.8.102:2181 --topic connect-offsets
bin/kafka-topics.sh --delete --zookeeper 10.255.8.102:2181 --topic connect-status

最后验证是否删除：

bin/kafka-topics.sh --list --zookeeper 10.255.8.102:2181

输出：

__consumer_offsets
ambari_kafka_service_check
connect-configs - marked for deletion
connect-offsets - marked for deletion
connect-status - marked for deletion

输出信息中显示三个connect topic已被标记删除了，要想彻底删除，需要在kafka的server.properties配置文件里设置delete.topic.enable=true