Hadoop 部署之 ZooKeeper (二)

一、Zookeeper功能簡介

ZooKeeper 是一個開源的分布式協調服務，由雅虎創建，是 Google Chubby 的開源實現。分布式應用程序可以基于 ZooKeeper 實現諸如數據發布/訂閱、負載均衡、命名服務、分布式協調/通知、集群管理、Master 選舉、配置維護，名字服務、分布式同步、分布式鎖和分布式隊列等功能。

二、ZooKeeper基本概念

1、集群角色

一個 ZooKeeper 集群同一時刻只會有一個 Leader，其他都是 Follower 或 Observer。

ZooKeeper 配置很簡單，每個節點的配置文件(zoo.cfg)都是一樣的，只有 myid 文件不一樣。myid 的值必須是 zoo.cfg中server.{數值} 的{數值}部分。

ZooKeeper 默認只有 Leader 和 Follower 兩種角色，沒有 Observer 角色。為了使用 Observer 模式，在任何想變成Observer的節點的配置文件中加入: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 的安裝

1、下載安裝(在datanode節點安裝)

下載安裝包

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

解壓安裝包

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

zk01節點(datanode1)配置id

echo "1">/home/zookeeper/myid

zk02節點(datanode2)配置id

echo "2">/home/zookeeper/myid

zk03節點(datanode3)配置id

echo "3">/home/zookeeper/myid

2、配置ZooKeeper環境變量

編輯文件/etc/profile.d/zookeeper.sh。

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

使ZK環境變量生效。

source /etc/profile.d/zookeeper.sh

3、配置 zoo.cfg

編輯文件/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

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

4、啟動各節點 ZK 服務

[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、查看各節點啟動狀態和角色

[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

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