06 | 服务器动态上下线监听案例

第 4 章 服务器动态上下线监听案例​

4.1 需求​

某分布式系统中，主节点可以有多台，可以动态上下线，任意一台客户端都能实时感知 到主节点服务器的上下线。

4.2 需求分析​

服务器动态上下线：客户端能实时洞察到服务器上下线的变化

4.3 具体实现​

(1)先在集群上创建/servers 节点

bash

[zk: localhost:2181(CONNECTED) 10] create /servers "servers"
Created /servers

(2)在 Idea 中创建包名: com.atguigu.zkcase1

(3)服务器端向 Zookeeper 注册代码

java

package com.atguigu.case1;

import org.apache.zookeeper.*;

import java.io.IOException;

public class DistributeServer {

    private String connectString = "127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183";
    private int sessionTimeout = 2000;
    private ZooKeeper zk;

    public static void main(String[] args) throws IOException, KeeperException, InterruptedException {
        
        DistributeServer server = new DistributeServer();
        // 1 获取zk连接
        server.getConnect();

        // 2 注册服务器到zk集群
        server.regist(args[0]);

        // 3 启动业务逻辑（睡觉）
        server.business();

    }

    // 业务功能
    private void business() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE);
    }
    
    // 注册服务器
    private void regist(String hostname) throws KeeperException, InterruptedException {
        String create = zk.create("/servers/" + hostname, hostname.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);

        System.out.println(hostname + " is online");
    }

    // 创建到 zk 的客户端连接
    private void getConnect() throws IOException {

        zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

            }
        });
    }
}

(4)客户端代码

java

package com.atguigu.case1;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class DistributeClient {

    private String connectString = "127.0.0.1:2181,127.0.0.1:2182,127.0.0.1:2183";
    private int sessionTimeout = 2000;
    private ZooKeeper zk;

    public static void main(String[] args) throws IOException, KeeperException, InterruptedException {
        DistributeClient client = new DistributeClient();

        // 1 获取zk连接
        client.getConnect();

        // 2 监听/servers下面子节点的增加和删除
        client.getServerList();

        // 3 业务逻辑（睡觉）
        client.business();

    }

    private void business() throws InterruptedException {
        Thread.sleep(Long.MAX_VALUE);
    }
    
    // 获取服务器列表信息
    private void getServerList() throws KeeperException, InterruptedException {
        // 1获取服务器子节点信息，并且对父节点进行监听
        List<String> children = zk.getChildren("/servers", true);

        // 2存储服务器信息列表
        ArrayList<String> servers = new ArrayList<>();

        // 3遍历所有节点，获取节点中的主机名称信息
        for (String child : children) {

            byte[] data = zk.getData("/servers/" + child, false, null);

            servers.add(new String(data));
        }

        // 4打印服务器列表信息
        System.out.println(servers);
    }

    private void getConnect() throws IOException {
        zk = new ZooKeeper(connectString, sessionTimeout, new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {

                try {
                    getServerList();
                } catch (KeeperException e) {
                    e.printStackTrace();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}

4.4 测试​

1)在 Linux 命令行上操作增加减少服务器

(1)启动 DistributeClient 客户端

(2)在 hadoop102 上 zk 的客户端/servers 目录上创建临时带序号节点

bash

[zk: localhost:2181(CONNECTED) 1] create -e -s /servers/hadoop102 "hadoop102"
[zk: localhost:2181(CONNECTED) 2] create -e -s /servers/hadoop103 "hadoop103"

(3)观察 Idea 控制台变化

bash

[hadoop102, hadoop103]

(4)执行删除操作

bash

[zk: localhost:2181(CONNECTED) 8] delete /servers/hadoop1020000000000

(5)观察 Idea 控制台变化

bash

[hadoop103]

2)在 Idea 上操作增加减少服务器

(1)启动 DistributeClient 客户端(如果已经启动过，不需要重启)

(2)启动 DistributeServer 服务

1点击 Edit Configurations...

2在弹出的窗口中(Program arguments)输入想启动的主机，例如，hadoop102

3回到 DistributeServer 的 main 方法，右键，在弹出的窗口中点击 Run “DistributeServer.main()”

4观察 DistributeServer 控制台，提示 hadoop102 is working

5观察 DistributeClient 控制台，提示 hadoop102 已经上线