1 Zookeeper Getting Started
1.1 Overview
Zookeeper is an open source distributed, to provide coordinated services to distributed applications Apache project.
1.2 Features
1.3 Data Structure
1.4 application scenarios
Services provided include: unified naming services, unified configuration management, unified cluster management, offline dynamic server node, soft load balancing.
Uniform Naming Service
Unified Configuration Management
The Unified Cluster Management
The server node dynamically offline
Soft Load Balancing
2 Zookeeper installation
2.1 Local installation deployment mode
1. Preparation Before Installation
(1) mounting the Jdk
(2) copies of the installation package Zookeeper Linux system
(3) to extract the specified directory
[root@topcheer mnt]# mkdir /opt/module/ [root@topcheer mnt]# tar -zxvf zookeeper-3.4.10.tar.gz -C /opt/module/ zookeeper-3.4.10/ zookeeper-3.4.10/LICENSE.txt zookeeper-3.4.10/lib/ zookeeper-3.4.10/lib/log4j-1.2.16.LICENSE.txt zookeeper-3.4.10/lib/cobertura/ zookeeper-3.4.10/lib/cobertura/README.txt zookeeper-3.4.10/lib/jline-0.9.94.LICENSE.txt
2．配置修改
（1）将/opt/module/zookeeper-3.4.10/conf这个路径下的zoo_sample.cfg修改为zoo.cfg；
[root@topcheer conf]# mv zoo_sample.cfg zoo.cfg [root@topcheer conf]# vim zoo.cfg
（2）打开zoo.cfg文件，修改dataDir路径：
修改如下内容：
dataDir=/opt/module/zookeeper-3.4.10/zkData
（3）在/opt/module/zookeeper-3.4.10/这个目录上创建zkData文件夹
[root@topcheer conf]# mkdir /opt/module/zookeeper-3.4.10/zkData
3．操作Zookeeper
（1）启动Zookeeper
[root@topcheer zookeeper-3.4.10]# bin/zkServer.sh start ZooKeeper JMX enabled by default Using config: /opt/module/zookeeper-3.4.10/bin/../conf/zoo.cfg Starting zookeeper ... STARTED
（2）查看状态：
[root@topcheer zookeeper-3.4.10]# bin/zkServer.sh status ZooKeeper JMX enabled by default Using config: /opt/module/zookeeper-3.4.10/bin/../conf/zoo.cfg Mode: standalone [root@topcheer zookeeper-3.4.10]#
（4）启动客户端：
[root@topcheer zookeeper-3.4.10]# bin/zkCli.sh Connecting to localhost:2181 2019-12-17 21:42:58,170 [myid:] - INFO [main:Environment@100] - Client environment:zookeeper.version=3.4.10-39d3a4f269333c922ed3db283be479f9deacaa0f, built on 03/23/2017 10:13 GMT 2019-12-17 21:42:58,185 [myid:] - INFO [main:Environment@100] - Client environment:host.name=topcheer 2019-12-17 21:42:58,186 [myid:] - INFO [main:Environment@100] - Client environment:java.version=1.8.0_181 2019-12-17 21:42:58,194 [myid:] - INFO [main:Environment@100] - Client environment:java.vendor=Oracle Corporation 2019-12-17 21:42:58,194 [myid:] - INFO [main:Environment@100] - Client environment:java.home=/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre 2019-12-17 21:42:58,194 [myid:] - INFO [main:Environment@100] - Client environment:java.class.path=/opt/module/zookeeper-3.4.10/bin/../build/classes:/opt/module/zookeeper-3.4.10/bin/../build/lib/*.jar:/opt/module/zookeeper-3.4.10/bin/../lib/slf4j-log4j12-1.6.1.jar:/opt/module/zookeeper-3.4.10/bin/../lib/slf4j-api-1.6.1.jar:/opt/module/zookeeper-3.4.10/bin/../lib/netty-3.10.5.Final.jar:/opt/module/zookeeper-3.4.10/bin/../lib/log4j-1.2.16.jar:/opt/module/zookeeper-3.4.10/bin/../lib/jline-0.9.94.jar:/opt/module/zookeeper-3.4.10/bin/../zookeeper-3.4.10.jar:/opt/module/zookeeper-3.4.10/bin/../src/java/lib/*.jar:/opt/module/zookeeper-3.4.10/bin/../conf: 2019-12-17 21:42:58,195 [myid:] - INFO [main:Environment@100] - Client environment:java.library.path=/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib:/usr/lib 2019-12-17 21:42:58,195 [myid:] - INFO [main:Environment@100] - Client environment:java.io.tmpdir=/tmp 2019-12-17 21:42:58,195 [myid:] - INFO [main:Environment@100] - Client environment:java.compiler=<NA> 2019-12-17 21:42:58,195 [myid:] - INFO [main:Environment@100] - Client environment:os.name=Linux 2019-12-17 21:42:58,195 [myid:] - INFO [main:Environment@100] - Client environment:os.arch=amd64 2019-12-17 21:42:58,196 [myid:] - INFO [main:Environment@100] - Client environment:os.version=3.10.0-957.el7.x86_64 2019-12-17 21:42:58,196 [myid:] - INFO [main:Environment@100] - Client environment:user.name=root 2019-12-17 21:42:58,196 [myid:] - INFO [main:Environment@100] - Client environment:user.home=/root 2019-12-17 21:42:58,196 [myid:] - INFO [main:Environment@100] - Client environment:user.dir=/opt/module/zookeeper-3.4.10 2019-12-17 21:42:58,198 [myid:] - INFO [main:ZooKeeper@438] - Initiating client connection, connectString=localhost:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@277050dc Welcome to ZooKeeper! 2019-12-17 21:42:58,240 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1032] - Opening socket connection to server localhost/127.0.0.1:2181. Will not attempt to authenticate using SASL (unknown error) JLine support is enabled 2019-12-17 21:42:58,392 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@876] - Socket connection established to localhost/127.0.0.1:2181, initiating session 2019-12-17 21:42:58,467 [myid:] - INFO [main-SendThread(localhost:2181):ClientCnxn$SendThread@1299] - Session establishment complete on server localhost/127.0.0.1:2181, sessionid = 0x16f140b9b8f0000, negotiated timeout = 30000 WATCHER:: WatchedEvent state:SyncConnected type:None path:null [zk: localhost:2181(CONNECTED) 0]
（5）退出客户端：
[zk: localhost:2181(CONNECTED) 0] quit Quitting... 2019-12-17 21:43:32,790 [myid:] - INFO [main:ZooKeeper@684] - Session: 0x16f140b9b8f0000 closed 2019-12-17 21:43:32,793 [myid:] - INFO [main-EventThread:ClientCnxn$EventThread@519] - EventThread shut down for session: 0x16f140b9b8f0000 [root@topcheer zookeeper-3.4.10]#
（6）停止Zookeeper
[root@topcheer zookeeper-3.4.10]# bin/zkServer.sh stop
2.2 配置参数解读
Zookeeper中的配置文件zoo.cfg中参数含义解读如下：
1．tickTime =2000：通信心跳数，Zookeeper服务器与客户端心跳时间，单位毫秒
Zookeeper使用的基本时间，服务器之间或客户端与服务器之间维持心跳的时间间隔，也就是每个tickTime时间就会发送一个心跳，时间单位为毫秒。
它用于心跳机制，并且设置最小的session超时时间为两倍心跳时间。(session的最小超时时间是2*tickTime)
2．initLimit =10：LF初始通信时限
集群中的Follower跟随者服务器与Leader领导者服务器之间初始连接时能容忍的最多心跳数（tickTime的数量），用它来限定集群中的Zookeeper服务器连接到Leader的时限。
3．syncLimit =5：LF同步通信时限
集群中Leader与Follower之间的最大响应时间单位，假如响应超过syncLimit * tickTime，Leader认为Follwer死掉，从服务器列表中删除Follwer。
4．dataDir：数据文件目录+数据持久化路径
主要用于保存Zookeeper中的数据。
5．clientPort =2181：客户端连接端口
监听客户端连接的端口。