问题：
服务网注册到Zookeeper注册中心，启动项目，显示下面异常：

org.apache.zookeeper.KeeperException$ConnectionLossException: KeeperErrorCode = ConnectionLoss
    at org.apache.zookeeper.KeeperException.create(KeeperException.java:99) ~[zookeeper-3.5.3-beta.jar:3.5.3-beta-8ce24f9e675cbefffb8f21a47e06b42864475a60]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl.checkBackgroundRetry(CuratorFrameworkImpl.java:844) [curator-framework-4.0.1.jar:4.0.1]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl.performBackgroundOperation(CuratorFrameworkImpl.java:972) [curator-framework-4.0.1.jar:4.0.1]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl.backgroundOperationsLoop(CuratorFrameworkImpl.java:925) [curator-framework-4.0.1.jar:4.0.1]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl.access$300(CuratorFrameworkImpl.java:73) [curator-framework-4.0.1.jar:4.0.1]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl$4.call(CuratorFrameworkImpl.java:322) [curator-framework-4.0.1.jar:4.0.1]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_201]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_201]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_201]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_201]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_201]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201]


2020-05-03 10:33:23.819 ERROR 3740 --- [tor-Framework-0] o.a.c.f.imps.CuratorFrameworkImpl        : Background retry gave up


org.apache.curator.CuratorConnectionLossException: KeeperErrorCode = ConnectionLoss
    at org.apache.curator.framework.imps.CuratorFrameworkImpl.performBackgroundOperation(CuratorFrameworkImpl.java:954) [curator-framework-4.0.1.jar:4.0.1]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl.backgroundOperationsLoop(CuratorFrameworkImpl.java:925) [curator-framework-4.0.1.jar:4.0.1]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl.access$300(CuratorFrameworkImpl.java:73) [curator-framework-4.0.1.jar:4.0.1]
    at org.apache.curator.framework.imps.CuratorFrameworkImpl$4.call(CuratorFrameworkImpl.java:322) [curator-framework-4.0.1.jar:4.0.1]
    at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_201]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180) [na:1.8.0_201]
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293) [na:1.8.0_201]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_201]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_201]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_201]


2020-05-03 10:33:25.702  WARN 3740 --- [168.5.131:2181)] org.apache.zookeeper.ClientCnxn          : Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect


java.net.ConnectException: Connection timed out: no further information
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method) ~[na:1.8.0_201]
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717) ~[na:1.8.0_201]
    at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:357) ~[zookeeper-3.5.3-beta.jar:3.5.3-beta-8ce24f9e675cbefffb8f21a47e06b42864475a60]
    at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1214) ~[zookeeper-3.5.3-beta.jar:3.5.3-beta-8ce24f9e675cbefffb8f21a47e06b42864475a60]

解决方案：
1、安装Zookeeper的服务器防火墙没关闭
2、若防火墙已关闭，则可能是 private static final int sessionTimeout = 10000 中设置的sessionTimeout值太小，应增大此值。

说明： sessionTimeout是会话超时时间，也就是当一个zookeeper超过该时间没有心跳，则认为该节点故障。所以，如果此值小于zookeeper的创建时间，则当zookeeper还未来得及创建连接，会话时间已到，因此抛出异常认为该节点故障。