搭建zookeeper环境

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

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