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ZooKeeper实践：（2）集群管理
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("10.32.180.251:2181", 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
ZooKeeper实践：（2）集群管理