前言：
随着业务的扩大，用户的增多，访问量的增加，单机模式已经不能支撑，从而出现了从单机模式->垂直应用模式->集群模式，集群模式诞生了，伴随着一堆问题也油然而生，Master怎么选举，机器故障及时移除集群，添加机器了如何及时的感应到，Zookeeper不仅能维护当前的集群服务状态，还能及时的选出master，它们的实现方式都是在Zookeeper上面注册一个EPHEMERAL目录节点，在创建目录的父目录上面调用getChildren(String path,boolean watch)设置watch为true，注册watcher事件，由于是临时节点，当服务器出现问题造成session丢失，相对应的目录节点随之删除，Children节点发生变化，就会调用前面注册的watcher，使集群内的每个节点都得到新的集群信息。反之，新增节点也是这样。
注：master选举，不同之处是注册一个EPHEMERAL_SEQUENTIAL 目录节点，我们可以选择最小编号为master，实现了动态选择master，避免master出现单点故障
一、架构体系
二：模拟代码
监控类：
package com.zk.config.manager; import java.io.IOException;
import java.util.Collections;
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.ZooKeeper;
import org.apache.zookeeper.Watcher.Event.EventType;
import org.apache.zookeeper.Watcher.Event.KeeperState;
import org.apache.zookeeper.ZooDefs.Ids; public class AppRegister { private CountDownLatch connectedSemaphore = new CountDownLatch(1);
private ZooKeeper zooKeeper;
private Object lock = new Object();
private String ip; private String rootConfig; public AppRegister(String ip, String root) {
this.ip = ip;
this.rootConfig = root;
this.zooKeeper = connectZookeeper(); } public ZooKeeper connectZookeeper() {
synchronized (lock) {
if (zooKeeper == null) {
try {
zooKeeper = new ZooKeeper("192.168.1.1:2181", 5000, new Watcher() {
public void process(WatchedEvent event) {
if (KeeperState.SyncConnected == event.getState()) {
if (EventType.None == event.getType() && null == event.getPath()) {
try {
connectedSemaphore.countDown();
zooKeeper.getChildren(rootConfig, true);
zooKeeper.create(rootConfig + "/" + ip, ip.getBytes(), Ids.OPEN_ACL_UNSAFE,
CreateMode.EPHEMERAL_SEQUENTIAL);
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
} else if (EventType.NodeChildrenChanged == event.getType()) {
try {
List<String> childrenList = zooKeeper.getChildren(rootConfig, true);
System.out.println("节点变化了：" + childrenList);
Collections.sort(childrenList);
System.out.println("我是master了：" + childrenList.get(0));
} catch (KeeperException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} } }
}
} );
connectedSemaphore.await();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} }
}
return zooKeeper;
}
}
模拟程序：
package com.zk.config.manager;
public class AppMonitor {
private final static String rootConfig = "/AppCluster";
public static void main(String[] args) throws InterruptedException {
/**
* 新增机器,选举master
*/
addHost();
Thread.sleep(Integer.MAX_VALUE);
}
private static void addHost()
{
new Thread(new Runnable() {
public void run() {
new AppRegister("192.168.1.1", rootConfig);
}
}).start();
new Thread(new Runnable() {
public void run() {
try {
Thread.sleep(2000);
new AppRegister("192.168.1.2", rootConfig);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}).start();
}
}
运行结果：
节点变化了：[192.168.1.10000000029]
我是master了：192.168.1.10000000029
节点变化了：[192.168.1.20000000030, 192.168.1.10000000029]
我是master了：192.168.1.10000000029
节点变化了：[192.168.1.20000000030, 192.168.1.10000000029]
我是master了：192.168.1.10000000029