ZooKeeper是一个分布式的，开放源码的分布式应用程序协调服务，它包含一个简单的原语集，分布式应用程序可以基于它实现同步服务，配置维护和命名服务等。
设计目的
1.最终一致性：client不论连接到哪个Server，展示给它都是同一个视图，这是zookeeper最重要的性能。
2 .可靠性：具有简单、健壮、良好的性能，如果消息m被到一台服务器接受，那么它将被所有的服务器接受。
3 .实时性：Zookeeper保证客户端将在一个时间间隔范围内获得服务器的更新信息，或者服务器失效的信息。但由于网络延时等原因，Zookeeper不能保证两个客户端能同时得到刚更新的数据，如果需要最新数据，应该在读数据之前调用sync()接口。
4 .等待无关（wait-free）：慢的或者失效的client不得干预快速的client的请求，使得每个client都能有效的等待。
5.原子性：更新只能成功或者失败，没有中间状态。
6 .顺序性：包括全局有序和偏序两种：全局有序是指如果在一台服务器上消息a在消息b前发布，则在所有Server上消息a都将在消息b前被发布；偏序是指如果一个消息b在消息a后被同一个发送者发布，a必将排在b前面。
ZK安装分为单机安装、伪分布安装和分布式安装
一、单机安装
[root@node1 bin]# wget http://apache.opencas.org/zookeeper/zookeeper-3.4.6/zookeeper-3.4.6.tar.gz
[root@node1 zk]# ls
zookeeper-3.4.6.tar.gz
[root@node1 zk]# tar -zxvf zookeeper-3.4.6.tar.gz
[root@node1 zk]# ls
zookeeper-3.4.6 zookeeper-3.4.6.tar.gz
[root@node1 zk]# mv zookeeper-3.4.6 zookeeper
[root@node1 zk]# cd zookeeper
[root@node1 zookeeper]# ls
bin CHANGES.txt contrib docs ivy.xml LICENSE.txt README_packaging.txt recipes zookeeper-3.4.6.jar zookeeper-3.4.6.jar.md5
build.xml conf dist-maven ivysettings.xml lib NOTICE.txt README.txt src zookeeper-3.4.6.jar.asc zookeeper-3.4.6.jar.sha1
[root@node1 zookeeper]# cd conf/
[root@node1 conf]# ls
configuration.xsl log4j.properties zoo_sample.cfg
[root@node1 conf]# cp zoo_sample.cfg zoo.cfg
[root@node1 conf]# cat zoo.cfg
# 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=/tmp/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
[root@node1 conf]# java -version
java version "1.7.0_45"
OpenJDK Runtime Environment (rhel-2.4.3.3.el6-i386 u45-b15)
OpenJDK Client VM (build 24.45-b08, mixed mode, sharing)
[root@node1 conf]# cd ../
[root@node1 zookeeper]# cd bin/
[root@node1 bin]# ls
README.txt zkCleanup.sh zkCli.cmd zkCli.sh zkEnv.cmd zkEnv.sh zkServer.cmd zkServer.sh
[root@node1 bin]# ./zkServer.sh
JMX enabled by default
Using config: /opt/zk/zookeeper/bin/../conf/zoo.cfg
Usage: ./zkServer.sh {start|start-foreground|stop|restart|status|upgrade|print-cmd}
[root@node1 bin]# ./zkServer.sh start
JMX enabled by default
Using config: /opt/zk/zookeeper/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED
[root@node1 bin]# jps
4341 Jps
4325 QuorumPeerMain
二、伪分布式安装
安装技巧：注意修改clientPort端口号，建议依次改为2181、2182、2183，写入myId文件,必须和Server.X里面的序号对应
server.1=127.0.0.1:2888:3888
server.2=127.0.0.1:2889:3889
server.3=127.0.0.1:2890:3890
[root@node1 conf]# vi zoo.cfg
# 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=../zkdata
# 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=127.0.0.1:2888:3888
server.2=127.0.0.1:2889:3889
server.3=127.0.0.1:2890:3890
~
"zoo.cfg" 33L, 1007C written
[root@node1 conf]# cd ../
[root@node1 zookeeper]# mkdir zkdata
[root@node1 zookeeper]# cd ../
[root@node1 zk]# clear
[root@node1 zk]# ls
zookeeper zookeeper-3.4.6.tar.gz
[root@node1 zk]# cp -R zookeeper zookeeper2
[root@node1 zk]# cp -R zookeeper zookeeper3
[root@node1 zk]# jps
4372 Jps
4325 QuorumPeerMain
[root@node1 zk]# kill -9 4325
[root@node1 zk]# jps
4381 Jps
[root@node1 zk]# echo 1 > zookeeper/zkdata/myid
[root@node1 zk]# echo 2 > zookeeper2/zkdata/myid
[root@node1 zk]# echo 3 > zookeeper3/zkdata/myid
[root@node1 zk]# echo 2 > zookeeper2/zkdata/myid
[root@node1 zk]# cat zookeeper3/zkdata/myid
3
[root@node1 zk]# cat zookeeper2/zkdata/myid
2
[root@node1 zk]# cat zookeeper/zkdata/myid
1
[root@node1 zk]#
启动验证
/opt/zk/zookeeper/bin/zkServer.sh start-foreground
/opt/zk/hadoop/zookeeper2/bin/zkServer.sh start-foreground
/opt/zk/hadoop/zookeeper3/bin/zkServer.sh start-foreground
启用成功后，输入 jps 看下进程
三、分布式安装
修改单机安装的zoo.cfg文件，如下图所示，因为是分布式安装，所以下图表红色部分，只需要修改对应的IP地址即可[root@node1 conf]# vi zoo.cfg
# 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=../zkdata
# 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=192.168.1.1:2888:3888
server.2=192.168.1.2:2888:3888
server.3=192.168.1.3:2888:3888
~
步骤二、通过Scp命令分发文件到其余两台机器上面
步骤三、修改各自的myid文件，必须和zoo.cfg里面配置的server.1=192.168.1.1数字和IP对应起来
[root@node1 zk]# echo 1 > zookeeper/zkdata/myid
步骤四、启动验证/opt/zk/zookeeper/bin/zkServer.sh start-foreground