hadoop高可用集群启动yarn失败，通过查看日志信息发现主要错误如下：
org.apache.zookeeper.ClientCnxn: Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect java.net.ConnectException: 拒绝连接
org.apache.zookeeper.ClientCnxn: Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect java.net.ConnectException: 拒绝连接
Hadoop依赖Zookeeper实现HDFS集群的高可用，我这里zookeeper集群没有正常启动
导致了yarn集群启动失败
把zookeeper集群正常启动后就没问题了。
