今天安装配置三台zookeeper服务集群，配置内容如下：
# The number of milliseconds of each tick
tickTime=2000
# The number of ticks that the initial
# synchronization phase can take
initLimit=10
# The number of ticks that can pass between
# sending a request and getting an acknowledgement
syncLimit=5
# the directory where the snapshot is stored.
# do not use /tmp for storage, /tmp here is just
# example sakes.
dataDir=/var/zookeeper
# the port at which the clients will connect
clientPort=2181
# the maximum number of client connections.
# increase this if you need to handle more clients
#maxClientCnxns=60
#
# Be sure to read the maintenance section of the
# administrator guide before turning on autopurge.
#
# http://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_maintenance
#
# The number of snapshots to retain in dataDir
#autopurge.snapRetainCount=3
# Purge task interval in hours
# Set to "0" to disable auto purge feature
#autopurge.purgeInterval=1
server.1=192.168.249.97:2888:3888
server.2=192.168.249.157:2888:3888
server.1=192.168.249.187:2888:3888
安装配置完毕后，逐一启动三台服务器
（1）master
（2）slave0
（3）slave1
集群中三个zookeeper服务显示正常启动。然后在master服务器使用的telnet 命令检测集群工作状态，
[root@master bin]# telnet 127.0.0.1 2181
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
stat
This ZooKeeper instance is not currently serving requests
Connection closed by foreign host.
[root@master bin]# This ZooKeeper instance is not currently serving requestsUnable to read additional data from server sessionid 0x0, likely server has closed socket, closing socket connection and attempting reconnect。
显示集群无法进行正常服务，后使用zkCli客户端进行连接测试。
2018-06-08 23:05:37,441 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1161] - Unable to read additional data from server sessionid 0x0, likely server has closed socket, closing socket connection and attempting reconnect
2018-06-08 23:05:38,673 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1028] - Opening socket connection to server localhost/0:0:0:0:0:0:0:1:2181. Will not attempt to authenticate using SASL (unknown error)
2018-06-08 23:05:38,674 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@878] - Socket connection established to localhost/0:0:0:0:0:0:0:1:2181, initiating session
2018-06-08 23:05:38,677 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1161] - Unable to read additional data from server sessionid 0x0, likely server has closed socket, closing socket connection and attempting reconnect
2018-06-08 23:05:39,571 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1028] - Opening socket connection to server localhost/127.0.0.1:2181. Will not attempt to authenticate using SASL (unknown error)
2018-06-08 23:05:39,572 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@878] - Socket connection established to localhost/127.0.0.1:2181, initiating session
2018-06-08 23:05:39,576 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1161] - Unable to read additional data from server sessionid 0x0, likely server has closed socket, closing socket connection and attempting reconnect
2018-06-08 23:05:41,349 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1028] - Opening socket connection to server localhost/0:0:0:0:0:0:0:1:2181. Will not attempt to authenticate using SASL (unknown error)
2018-06-08 23:05:41,351 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@878] - Socket connection established to localhost/0:0:0:0:0:0:0:1:2181, initiating session
2018-06-08 23:05:41,352 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1161] - Unable to read additional data from server sessionid 0x0, likely server has closed socket, closing socket connection and attempting reconnect
客户端也显示无法进行正常的服务。
这种情况原因是集群没有能够选举出Leader，在启动时正常已经启动三个机器的zookeeper服务，因此，可能是防火墙导致zookeeper服务端口无法进行相互访问。在集群中每台机器中配置防火墙设置。
firewall-cmd --zone=public --add-port=2181/tcp --permanent
firewall-cmd --zone=public --add-port=2888/tcp --permanent
firewall-cmd --zone=public --add-port=3888/tcp --permanent
firewall-cmd --reload
逐次重新启动，zookeeper，OK。
