一、什么是ZooKeeper？
ZooKeeper（动物园管理员），顾名思义，是用来管理Hadoop（大象）、Hive（蜜蜂）、Pig（小猪）的管理员，同时Apache HBase、Apache Solr、LinkedIn Sensei等众多项目中都采用了ZooKeeper。
ZooKeeper是一个集中式服务，用于维护配置信息、命名、提供分布式同步和提供组服务。所有这些类型的服务都以某种形式被分布式应用程序使用。每次它们被实现时，都有大量的工作用于修复不可避免的bug和竞选条件。由于实现这类服务的困难，应用程序最初通常跳过它们，这使得它们在存在更改时变得脆弱，并且难以管理。即使正确完成，这些服务的不同实现也会在部署应用程序时导致管理复杂性。
二、Zookeeper集群
Kafka使用Zookeeper来存储集群元数据以及消费者元数据。Zookeeper集群被称为群组。Zookeeper使用的是一致性协议，所以建议每个群组里应该包含奇数个节点（比如3个、5个等），因为只有当群组里的大多数节点（也就是法定人数）处于可用状态，Zookeeper才能处理外部的请求。也就是说，如果3个节点的集群，允许1个节点失效。如果5个节点的集群，允许2个节点失效。
三、Docker方式配置ZooKeeper
myid文件：标识要写到快照目录下面myid文件里
采用Docker镜像：wurstmeister/zookeeper，部署一个3节点的集群。
节点一：
- docker-compose.yml
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- myid文件
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- zoo.cfg文件
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36# 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=/opt/zookeeper-3.4.9/data
dataLogDir=/opt/zookeeper-3.4.9/logs
# 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
#kafka01 (10.100.158.245)
server.1=0.0.0.0:2888:3888
#kafka02 (10.100.19.15)
server.2=10.150.19.15:2888:3888
#kafka03 (10.100.124.217)
server.3=10.100.124.217:2888:3888
节点二：
- docker-compose.yml
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14version: '2'
services:
zookeeper:
image: wurstmeister/zookeeper
volumes:
- ./zoo.cfg:/opt/zookeeper-3.4.9/conf/zoo.cfg
- ./data:/opt/zookeeper-3.4.9/data
- ./logs:/opt/zookeeper-3.4.9/logs
- ./myid:/opt/zookeeper-3.4.9/data/myid
ports:
- "2180:2181"
- "2888:2888"
- "3888:3888"
restart: always - myid文件
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- zoo.cfg文件
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36# 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=/opt/zookeeper-3.4.9/data
dataLogDir=/opt/zookeeper-3.4.9/logs
# 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
#kafka01 (10.100.158.245)
server.1=10.100.158.245:2888:3888
#kafka02 (10.100.19.15)
server.2=0.0.0.0:2888:3888
#kafka03 (10.100.124.217)
server.3=10.100.124.217:2888:3888节点三：
- docker-compose.yml
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14version: '2'
services:
zookeeper:
image: wurstmeister/zookeeper
volumes:
- ./zoo.cfg:/opt/zookeeper-3.4.9/conf/zoo.cfg
- ./data:/opt/zookeeper-3.4.9/data
- ./logs:/opt/zookeeper-3.4.9/logs
- ./myid:/opt/zookeeper-3.4.9/data/myid
ports:
- "2179:2181"
- "2888:2888"
- "3888:3888"
restart: always - myid文件
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- zoo.cfg文件
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36# 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=/opt/zookeeper-3.4.9/data
dataLogDir=/opt/zookeeper-3.4.9/logs
# 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
#kafka01 (10.100.158.245)
server.1=10.100.158.245:2888:3888
#kafka02 (10.100.19.15)
server.2=10.100.19.15:2888:3888
#kafka03 (10.100.124.217)
server.3=0.0.0.0:2888:3888
四、查看ZooKeeper状态
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停掉leader，2个follower的状态有变化，如下：
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再次查看status:
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服务器3变成leader了！
重新启动服务器1，服务器1是follower
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