Hadoop 部署之 ZooKeeper (二)

一、Zookeeper功能简介

ZooKeeper 是一个开源的分布式协调服务，由雅虎创建，是 Google Chubby 的开源实现。分布式应用程序可以基于 ZooKeeper 实现诸如数据发布/订阅、负载均衡、命名服务、分布式协调/通知、集群管理、Master 选举、配置维护，名字服务、分布式同步、分布式锁和分布式队列等功能。

二、ZooKeeper基本概念

1、集群角色

一个 ZooKeeper 集群同一时刻只会有一个 Leader，其他都是 Follower 或 Observer。

ZooKeeper 配置很简单，每个节点的配置文件(zoo.cfg)都是一样的，只有 myid 文件不一样。myid 的值必须是 zoo.cfg中server.{数值} 的{数值}部分。

ZooKeeper 默认只有 Leader 和 Follower 两种角色，没有 Observer 角色。为了使用 Observer 模式，在任何想变成Observer的节点的配置文件中加入:peerType=observer 并在所有 server 的配置文件中，配置成 observer 模式的 server 的那行配置追加 :observer

三、ZooKeeper 的安装

1、下载安装(在datanode节点安装)

下载安装包

wget http://mirror.bit.edu.cn/apache/zookeeper/zookeeper-3.4.10/zookeeper-3.4.10.tar.gz

解压安装包

tar xf zookeeper-3.4.10.tar.gz
mv zookeeper-3.4.10 /usr/local/zookeeper
mkdir -p /home/zookeeper

zk01节点(datanode1)配置id

echo "1">/home/zookeeper/myid

zk02节点(datanode2)配置id

echo "2">/home/zookeeper/myid

zk03节点(datanode3)配置id

echo "3">/home/zookeeper/myid

2、配置ZooKeeper环境变量

编辑文件/etc/profile.d/zookeeper.sh。

# ZOOKEEPER ENV
export ZOOKEEPER_HOME=/usr/local/zookeeper
export PATH=$PATH:$ZOOKEEPER_HOME/bin

使ZK环境变量生效。

source /etc/profile.d/zookeeper.sh

3、配置 zoo.cfg

编辑文件/usr/local/zookeeper/conf/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=/home/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
server.1=zk01:2888:3888
server.2=zk02:2888:3888
server.3=zk03:2888:3888

比较重要的配置如下：
dataDir=/home/zookeeper
server.1=zk01:2888:3888
server.2=zk02:2888:3888
server.3=zk03:2888:3888

4、启动各节点 ZK 服务

[root@datanode01 ~]# zkServer.sh start
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED

[root@datanode02 ~]# zkServer.sh start
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED

[root@datanode03 ~]# zkServer.sh start
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED

5、查看各节点启动状态和角色

[root@datanode01 ~]# zkServer.sh status
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Mode: follower

[root@datanode02 ~]# zkServer.sh status
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Mode: leader

[root@datanode03 ~]# zkServer.sh status
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Mode: follower

官方文档：https://zookeeper.apache.org/doc/current/zookeeperStarted.html