前言： 隨著業務的擴大，用戶的增多，訪問量的增加，單機模式已經不能支撐，從而出現了從單機模式->垂直應用模式->集群模式，集群模式誕生了，伴隨著一堆問題也油然而生，Master怎麼選舉，機器故障及時移除集群，添加機器瞭如何及時的感應到，Zookeeper不僅能維護當前的集群服務狀態，還能及時的選出m ...
前言：
隨著業務的擴大，用戶的增多，訪問量的增加，單機模式已經不能支撐，從而出現了從單機模式->垂直應用模式->集群模式，集群模式誕生了，伴隨著一堆問題也油然而生，Master怎麼選舉，機器故障及時移除集群，添加機器瞭如何及時的感應到，Zookeeper不僅能維護當前的集群服務狀態，還能及時的選出master，它們的實現方式都是在Zookeeper上面註冊一個EPHEMERAL目錄節點，在創建目錄的父目錄上面調用getChildren(String path,boolean watch)設置watch為true，註冊watcher事件，由於是臨時節點，當伺服器出現問題造成session丟失，相對應的目錄節點隨之刪除，Children節點發生變化，就會調用前面註冊的watcher，使集群內的每個節點都得到新的集群信息。反之，新增節點也是這樣。
註：master選舉，不同之處是註冊一個EPHEMERAL_SEQUENTIAL 目錄節點，我們可以選擇最小編號為master，實現了動態選擇master，避免master出現單點故障
一、架構體系
二：模擬代碼
監控類：
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("節點變化了：" + 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;
}
}
模擬程式：
package com.zk.config.manager;
public class AppMonitor {
private final static String rootConfig = "/AppCluster";
public static void main(String[] args) throws InterruptedException {
/**
* 新增機器,選舉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();
}
}
運行結果：
節點變化了：[192.168.1.10000000029]
我是master了：192.168.1.10000000029
節點變化了：[192.168.1.20000000030, 192.168.1.10000000029]
我是master了：192.168.1.10000000029
節點變化了：[192.168.1.20000000030, 192.168.1.10000000029]
我是master了：192.168.1.10000000029
