ZooKeeper

ZooKeeper是一个开源的分布式协调服务，他为分布式应用提供了高效且可靠的分布式协调服务，提供了诸如统一命名空间服务，配置服务和分布式锁等分布式基础服务。

就是一个服务注册中心。一个典型的ZooKeeper集群如下：

ZooKeeper拥有一个层次的命名空间，这个和标准的文件系统非常相似，如下图所示：

安装

1. 下载并解压；
2. 创建data和log目录；

3. 修改config - zoo.cfg；

   dataDir=/opt/zookeeper-3.4.13/data
   dataLogDir=/opt/zookeeper-3.4.13/log

4. 启动

   [root@Automation bin]# ./zkServer.sh startZooKeeper JMX enabled by defaultUsing config: /opt/zookeeper-3.4.13/bin/../conf/zoo.cfgStarting zookeeper ... STARTED[root@Automation bin]# ./zkServer.sh statusZooKeeper JMX enabled by defaultUsing config: /opt/zookeeper-3.4.13/bin/../conf/zoo.cfgMode: standalone
   ZooKeeper JMX enabled by default
   Using config: /opt/zookeeper-3.4.13/bin/../conf/zoo.cfg
   Starting zookeeper ... STARTED
   [root@Automation bin]# ./zkServer.sh status
   ZooKeeper JMX enabled by default
   Using config: /opt/zookeeper-3.4.13/bin/../conf/zoo.cfg
   Mode: standalone

命令操作

[root@Automation bin]# ./zkCli.sh -server localhost:2181
Connecting to localhost:2181
2018-06-02 09:26:12,387 [myid:] - INFO  [main:Environment@100] - Client environment:zookeeper.version=3.4.13-2d71af4dbe22557fda74f9a9b4309b15a7487f03, built on 06/29/2018 04:05 GMT
2018-06-02 09:26:12,395 [myid:] - INFO  [main:Environment@100] - Client environment:host.name=<NA>
2018-06-02 09:26:12,395 [myid:] - INFO  [main:Environment@100] - Client environment:java.version=1.8.0_11
2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.vendor=Oracle Corporation
2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.home=/usr/java/jdk1.8.0_11/jre
2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.class.path=/opt/zookeeper-3.4.13/bin/../build/classes:/opt/zookeeper-3.4.13/bin/../build/lib/*.jar:/opt/zookeeper-3.4.13/bin/../lib/slf4j-log4j12-1.7.25.jar:/opt/zookeeper-3.4.13/bin/../lib/slf4j-api-1.7.25.jar:/opt/zookeeper-3.4.13/bin/../lib/netty-3.10.6.Final.jar:/opt/zookeeper-3.4.13/bin/../lib/log4j-1.2.17.jar:/opt/zookeeper-3.4.13/bin/../lib/jline-0.9.94.jar:/opt/zookeeper-3.4.13/bin/../lib/audience-annotations-0.5.0.jar:/opt/zookeeper-3.4.13/bin/../zookeeper-3.4.13.jar:/opt/zookeeper-3.4.13/bin/../src/java/lib/*.jar:/opt/zookeeper-3.4.13/bin/../conf:.:/usr/java/jdk1.8.0_11/lib/dt.jar:/usr/java/jdk1.8.0_11/lib/tools.jar:/usr/java/jdk1.8.0_11/jre/lib2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.library.path=/usr/java/packages/lib/i386:/lib:/usr/lib2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.io.tmpdir=/tmp2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.compiler=<NA>2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:os.name=Linux2018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:os.arch=i3862018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:os.version=2.6.32-573.el6.x86_642018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:user.name=root2018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:user.home=/root2018-06-02 09:26:12,407 [myid:] - INFO  [main:Environment@100] - Client environment:user.dir=/opt/zookeeper-3.4.13/bin2018-06-02 09:26:12,410 [myid:] - INFO  [main:ZooKeeper@442] - Initiating client connection, connectString=localhost:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@1e0aca6Welcome to ZooKeeper!2018-06-02 09:26:12,484 [myid:] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1029] - Opening socket connection to server localhost/0:0:0:0:0:0:0:1:2181. Will not attempt to authenticate using SASL (unknown error)JLine support is enabled2018-06-02 09:26:12,510 [myid:] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@879] - Socket connection established to localhost/0:0:0:0:0:0:0:1:2181, initiating session2018-06-02 09:26:12,572 [myid:] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1303] - Session establishment complete on server localhost/0:0:0:0:0:0:0:1:2181, sessionid = 0x1003ae6d0d60000, negotiated timeout = 30000WATCHER::WatchedEvent state:SyncConnected type:None path:null[zk: localhost:2181(CONNECTED) 0]
2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.library.path=/usr/java/packages/lib/i386:/lib:/usr/lib
2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.io.tmpdir=/tmp
2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:java.compiler=<NA>
2018-06-02 09:26:12,405 [myid:] - INFO  [main:Environment@100] - Client environment:os.name=Linux
2018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:os.arch=i386
2018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:os.version=2.6.32-573.el6.x86_64
2018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:user.name=root
2018-06-02 09:26:12,406 [myid:] - INFO  [main:Environment@100] - Client environment:user.home=/root
2018-06-02 09:26:12,407 [myid:] - INFO  [main:Environment@100] - Client environment:user.dir=/opt/zookeeper-3.4.13/bin
2018-06-02 09:26:12,410 [myid:] - INFO  [main:ZooKeeper@442] - Initiating client connection, connectString=localhost:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@1e0aca6
Welcome to ZooKeeper!
2018-06-02 09:26:12,484 [myid:] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1029] - Opening socket connection to server localhost/0:0:0:0:0:0:0:1:2181. Will not attempt to authenticate using SASL (unknown error)
JLine support is enabled
2018-06-02 09:26:12,510 [myid:] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@879] - Socket connection established to localhost/0:0:0:0:0:0:0:1:2181, initiating session
2018-06-02 09:26:12,572 [myid:] - INFO  [main-SendThread(localhost:2181):ClientCnxn$SendThread@1303] - Session establishment complete on server localhost/0:0:0:0:0:0:0:1:2181, sessionid = 0x1003ae6d0d60000, negotiated timeout = 30000

WATCHER::

WatchedEvent state:SyncConnected type:None path:null
[zk: localhost:2181(CONNECTED) 0]

这里不做过多深入学习说明，集群环境搭建，工作原理，Leader选举等，请参见官方文档。