原因： 防火牆沒關閉
異常信息如下：
2020-01-07 22:55:12,255 [myid:2] - WARN [QuorumPeer[myid=2](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):QuorumCnxManager@679] - Cannot open channel to 1 at election address /192.168.31.130:3888
java.net.NoRouteToHostException: 沒有到主機的路由 (Host unreachable)
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:606)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:650)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:707)
at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:735)
at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:910)
at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:1247)
2020-01-07 22:55:12,256 [myid:2] - INFO [QuorumPeer[myid=2](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):FastLeaderElection@919] - Notification time out: 6400
CentOS7 關閉防火牆命令：
systemctl stop firewalld.service #停止firewall
systemctl disable firewalld.service #禁止firewall開機啓動
firewall-cmd --state #查看默認防火牆狀態（關閉後顯示notrunning，開啓後顯示running）
