测试用kafka生产者发送消息时候警告，因为，kafka集群没有全部起来，第一次只是启动了一个集群，所有有两个connection 节点找不到，第二次开启了节点2，节点2的警告消失，第三次全部节点开启，警告消失。
1.[trustfar@bigdata01 ~]$ kafka-console-producer.sh --broker-list bigdata01:9092,bigdata02:9092,bigdata03:9092 --topic test1

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[2019-03-15 20:07:38,810] WARN [Producer clientId=console-producer] Connection to node -2 could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)
[2019-03-15 20:07:38,922] WARN [Producer clientId=console-producer] Connection to node -2 could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)
[2019-03-15 20:07:38,926] WARN [Producer clientId=console-producer] Connection to node -3 could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)
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2.[trustfar@bigdata01 ~]$ kafka-console-producer.sh --broker-list bigdata01:9092,bigdata02:9092,bigdata03:9092 --topic test1

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[2019-03-15 20:13:13,629] WARN [Producer clientId=console-producer] Connection to node -3 could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)
[2019-03-15 20:13:13,749] WARN [Producer clientId=console-producer] Connection to node -3 could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)
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3.[trustfar@bigdata01 ~]$ kafka-console-producer.sh --broker-list bigdata01:9092,bigdata02:9092,bigdata03:9092 --topic test1

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