zookeeper是一个强一致的分布式数据库，由多个节点共同组成一个分布式集群，挂掉任意一个节点，数据库仍然可以正常工作。
独立模式
下载zookeeper打包文件，并进行解压
➜ ~ tar -xvzf apache-zookeeper-3.5.6-bin.tar.gz 进入zookeeper的解压目录，重命名conf目录下的配置文件
➜ apache-zookeeper-3.5.6-bin mv conf/zoo_sample.cfg conf/zoo.cfg
启动zookeeper，使用start-foreground启动到前台，方便查看服务的输出信息
➜ apache-zookeeper-3.5.6-bin bin/zkServer.sh start-foreground
仲裁模式
在zoo.cfg的基础上进行编辑，创建zoo_1.cfg、zoo_2.cfg及zoo_3.cfg
需要额外追加的配置信息。冒号分割的第二部分和第三部分为TCP端口号，分别用于仲裁通讯和群首选举。
server.1=127.0.0.1:2222:2223
server.2=127.0.0.1:3333:3334
server.3=127.0.0.1:4444:4445
当启动一个服务器时，我们需要知道启动的是哪个服务器。zookeeper通过读取dataDir下的名为myid的文件来获取服务器ID信息。
➜ zookeeper echo 1 > zoo_1/data/myid
➜ zookeeper echo 2 > zoo_2/data/myid
➜ zookeeper echo 3 > zoo_3/data/myid
启动服务，从zoo_1开始
➜ zoo_1 ~/apache-zookeeper-3.5.6-bin/bin/zkServer.sh start-foreground ./zoo_1.cfg
因为我们只启动了三个zookeeper中的一个，所以整个服务器还无法运行。
2020-01-01 12:08:37,016 [myid:1] - INFO [QuorumPeer[myid=1](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):QuorumPeer@1193] - LOOKING
2020-01-01 12:08:37,016 [myid:1] - INFO [QuorumPeer[myid=1](plain=/0:0:0:0:0:0:0:0:2181)(secure=disabled):FastLeaderElection@885] - New election. My id = 1, proposed zxid=0x0 2020-01-01 12:08:37,021 [myid:1] - WARN [WorkerSender[myid=1]:QuorumCnxManager@679] www.xinyueylzc.cn- Cannot open channel to 2 at election address /127.0.0.1:3334 java.net.ConnectException: Connection refused (Connection refused) ... 2020-01-01 12:08:37,031 [myid:1] - WARN [WorkerSender[myid=1]:QuorumCnxManager@679] - Cannot open channel to 3 at election address /127.0.0.1:4445 java.net.ConnectException: Connection refused (Connection refused) ... 启动第二个服务器，这样可以构成仲裁的法定人数
➜ zoo_2 ~/apache-zookeeper-3.5.6-bin/bin/zkServer.sh start-foreground ./zoo_2.cfg
服务器二被选择为群首
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2020-01-01 12:10:40,802 [myid:2] - INFO [QuorumPeer[myid=2](plain=/0:0:0:0:0:0:0:0:2182)(secure=disabled):Leader@464] - LEADING - LEADER ELECTION TOOK - 54 MS
2020-01-01 12:10:40,804 [myid:2] - INFO [QuorumPeer[myid=2](www.lafei6d.cn plain=/0:0:0:0:0:0:0:0:2182)(secure=disabled):FileTxnSnapLog@384] - Snapshotting: 0x0 to /tmp/zookeeper/zoo_2/data/version-2/snapshot.0 2020-01-01 12:10:40,812 [myid:2] - INFO [LearnerHandler-www.huizhonggjpt.cn /127.0.0.1:62308:LearnerHandler@406] - Follower sid: 1 : info : 127.0.0.1:2222:2223:participant 2020-01-01 12:10:40,816 [myid:2] - INFO [LearnerHandler-www.shentuylzc.cn /127.0.0.1:62308:ZKDatabase@295] - On disk txn sync enabled with snapshotSizeFactor 0.33 访问集群
➜ bin ./zkCli.sh -server 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183 发布与订阅的例子
启动一个zk_0，创建一个临时的znode节点：
[zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(CONNECTED) 9] create www.feishenbo.cn-e /master "this is master" Created /master 启动另一个zk_1, 给znode设置一个监视点：
[zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(CONNECTED) 3] ls /master true 'ls path [watch]' has been deprecated. Please use 'ls [-w] path' instead. [] 再启动另一个zk_2，给znode设置一个监视点：
[zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(CONNECTED) 1] ls /master true 'ls path [watch]' has been deprecated.www.jujinyule.com Please use 'ls [-w] path' instead. [] 在zk_0中删除掉master，zk_1和zk_2同时收到删除的通知消息
zk_0:
[zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(www.letianhuanchao.cn CONNECTED) 10] delete /master zk_1/zk_2: [zk: 127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183(CONNECTED) 2] WATCHER:: WatchedEvent state:SyncConnected type:NodeDeleted path:/master