ZooKeeper是一个具有高可用性的高性能协调服务。
ZooKeeper维护着一个树形层次结构，书中的节点被称为znode。znode可以用来存储数据，并且有一个与之相关联的ACL（权限），znode不能大于1M。
ZooKeeper 的详细介绍：请点这里
ZooKeeper 的下载地址：请点这里
相关阅读：
分布式服务框架 ZooKeeper -- 管理分布式环境中的数据
ZooKeeper使用场景
ZooKeeper主要用来解决分布式系统中的“部分失败”问题。部分失败是分布式系统的固有的特征，ZooKeeper不能根除部分失败，也不会隐藏部分失败；但是可以提供一组工具，使你在构建分布式应用时对部分失败进行处理。这主要利用的是观察者模式。
Hadoop内置了ZooKeeper，阿里的开源框架Dubbo、Otter等也都是用ZooKeeper作为协调服务。
安装和运行ZooKeeper
安装
wget
tar zxvf zookeeper-3.3.6.tar.gz
cd zookeeper-3.3.6
cp conf/zoo_sample.cfg conf/zoo.cfg
运行
bin/zkServer.sh start
测试是否正确运行：echo ruok | nc localhost 2181，如果启动成功，则返回imok
zkCli.sh命令行工具
bin/zkCli.sh -server localhost，连接到ZooKeeper，可以执行各种znode操作。
Java开发的znode操作代码
import java.io.IOException;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
public class ZkTest implements Watcher
{
private static final int SESSION_TIMEOUT = 5000;
private ZooKeeper zk;
private CountDownLatch connectedSignal = new CountDownLatch(1);
public void connect(String hosts) throws IOException,InterruptedException
{
zk = new ZooKeeper(hosts,SESSION_TIMEOUT,this);
connectedSignal.await();
}
@Override
public void process(WatchedEvent event)
{
if(event.getState() == KeeperState.SyncConnected)
{
connectedSignal.countDown();
}
}
//新建表示组的znode
public void create(String groupName) throws KeeperException,InterruptedException
{
String path = "/" + groupName;
String createdPath = zk.create(path,null/*data*/,Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
System.out.println("Created " + createdPath);
}
//用户将成员加入组中:临时成员
public void join(String groupName,String memberName) throws KeeperException,InterruptedException
{
String path = "/" + groupName + "/" + memberName;
String createdPath = zk.create(path,null/*data*/,Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL);
System.out.println("Joined " + createdPath);
}
//列出组成员
public void list(String groupName) throws KeeperException,InterruptedException
{
String path = "/" + groupName;
try
{
List<String> children = zk.getChildren(path,false);
if(children.isEmpty())
{
System.out.printf("No members in group %s\n",groupName);
System.exit(1);
}
for(String child:children)
{
System.out.println(child);
}
}
catch (KeeperException.NoNodeException e)
{
System.out.printf("No members in group %s\n",groupName);
System.exit(1);
}
}
//删除一个组及其所有成员
public void delete(String groupName) throws KeeperException,InterruptedException
{
String path = "/" + groupName;
try
{
List<String> children = zk.getChildren(path,false);
for(String child:children)
{
zk.delete(path + "/" + child,-1);
}
zk.delete(path,-1);
}
catch (KeeperException.NoNodeException e)
{
System.out.printf("Group %s does not exist\n",groupName);
System.exit(1);
}
}
public void close() throws InterruptedException
{
zk.close();
}
public static void main(String[] args) throws Exception
{
ZkTest zkTest = new ZkTest();
zkTest.connect("192.168.211.230");
//zkTest.create("longlonggroup");
//zkTest.join("longlonggroup", "aaa");
//Thread.sleep(60000); //这里睡60秒是为了让你通过zkCli.sh之类的工具看到/creategroup下的aaa这个临时节点
//zkTest.list("CMS");
//zkTest.delete("longlonggroup");
zkTest.close();
}
}