Zookeeper实现服务注册/发现

what that?

Zookeeper在分布式开发中使用频繁,但许多框架都对其进行了封装,初学者可能无法较好的理解其工作原理,该文章演示了使用Zookeeper实现服务注册,服务发现的简单demo,希望能达到抛砖引玉的效果;

why need RegisterCenter?

之所以需要访问注册和服务发现是因为分布式系统中,服务之间需要相互调用,但若每个服务自己维护一份依赖的服务信息的话,就显得很麻烦,且自身维护的数据无法保证其实时性,当依赖的服务信息发生变更时,无法及时获取更新,解决方案就是引入一个注册中心,服务提供方将自己的信息写入到注册中心,服务使用方从注册中心来获取服务信息; 如下图:

client表示服务使用方,server表示服务提供方

实现的效果: 客户端可自动发现服务信息,当服务状态发生变化时(上线,下线,更换地址),客户端可以及时响应变化,效果如下图:

效果演示

实现

1. 首先保证Zookeeper以安装启动,且可以正常访问

2. 创建Maven项目并添加Zookeeper的Java客户端依赖(注意版本号需>3.6)

   				<dependency>
               <groupId>org.apache.zookeeper</groupId>
               <artifactId>zookeeper</artifactId>
               <version>3.6.1</version>
           </dependency>
   

3. 编写服务提供方

   package com.jerry;
   
   import org.apache.zookeeper.CreateMode;
   import org.apache.zookeeper.KeeperException;
   import org.apache.zookeeper.ZooDefs;
   import org.apache.zookeeper.ZooKeeper;
   import org.apache.zookeeper.data.ACL;
   
   import java.io.IOException;
   import java.io.InputStream;
   import java.net.*;
   import java.nio.charset.StandardCharsets;
   import java.util.ArrayList;
   import java.util.Enumeration;
   
   import static java.net.InetAddress.getLocalHost;
   
   public class UserService {
   
       public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
           new UserService().serving();
       }
   
       public void serving() throws IOException, KeeperException, InterruptedException {
           //获取本机ip地址
           String ip = null;
           Enumeration<NetworkInterface> networkInterfaces = NetworkInterface.getNetworkInterfaces();
           while (networkInterfaces.hasMoreElements()) {
               NetworkInterface ni = (NetworkInterface) networkInterfaces.nextElement();
               Enumeration<InetAddress> nias = ni.getInetAddresses();
               while (nias.hasMoreElements()) {
                   InetAddress ia = (InetAddress) nias.nextElement();
                   if (!ia.isLinkLocalAddress() && !ia.isLoopbackAddress() && ia instanceof Inet4Address) {
                       ip = ia.getHostAddress();
                   }
               }
           }
           int port = 8988;
   
           //启动服务
           ServerSocket socket = new ServerSocket(port);
           System.out.println("服务器已启动...");
           //注册服务
           serverRegister(ip, port);
           //处理请求
           clientHandler(socket);
       }
   
       private void clientHandler(ServerSocket socket) throws IOException {
           while (true) {
               Socket accept = socket.accept();
               InputStream inputStream = accept.getInputStream();
               byte[] barr = new byte[1024];
               while (true) {
                   int size = inputStream.read(barr);
                   if (size == -1) {
                       //System.out.println("客户端已关闭..");
                       accept.close();
                       break;
                   }
                   String s = new String(barr, 0, size);
                   //输出客户端消息
                   System.out.println(accept.getInetAddress().getHostAddress() + ": " + s);
               }
           }
   
       }
   
       private void serverRegister(String ip, int port) throws IOException, KeeperException, InterruptedException {
           //注册服务
           ZooKeeper zooKeeper = new ZooKeeper("10.211.55.4", 2181, null);
           try {
               ArrayList<ACL> acl = new ArrayList<>();
               acl.add(new ACL(31, ZooDefs.Ids.ANYONE_ID_UNSAFE));
               zooKeeper.create("/userServer", (ip + ":" + port).getBytes(StandardCharsets.UTF_8), acl, CreateMode.EPHEMERAL);
               System.out.println("服务发布成功!");
           } catch (KeeperException | InterruptedException e) {
               e.printStackTrace();
               throw e;
           }
       }
   }
   

4. 编写服务服务使用方

   package com.yyh;
   
   import org.apache.zookeeper.*;
   
   import java.io.IOException;
   import java.io.OutputStream;
   import java.net.InetSocketAddress;
   import java.net.Socket;
   import java.util.Scanner;
   
   public class UserClient implements Watcher {
       String node = "/userServer"; //服务信息所在的节点 服务提供方和服务消费方一致
       private ZooKeeper zooKeeper;
       String server_ip;
       int server_port;
   
       public static void main(String[] args) throws Exception {
           //开始服务监听
           UserClient userClient = new UserClient();
           userClient.run();
           //当访问可用时与服务交互
           Scanner scanner = new Scanner(System.in);
           while (true){
               System.out.println("输入要发送的信息(e:退出)");
               String text = scanner.next();
               if (text.equals("e"))System.exit(-1);
               if (userClient.server_ip == null){
                   System.err.println("没有可用的服务...");
               }else {
                   userClient.sendToServer(text);
               }
           }
       }
   
       private void run() throws Exception {
           //连接zookeeper
           zooKeeper = new ZooKeeper("10.211.55.4:2181", 3000, null);
           //尝试获取服务信息
           getServerInfo();
           //添加对服务信息的永久监听
           zooKeeper.addWatch(node,this,AddWatchMode.PERSISTENT);
       }
   
       //获取服务信息
       private void getServerInfo()  {
           try {
               byte[] data = zooKeeper.getData(node, false, null);
               String[] infos = new String(data).split(":");
               server_ip = infos[0];
               server_port = Integer.parseInt(infos[1]);
               System.out.println("获取服务信息成功!");
               System.out.println(server_ip+":"+ server_port);
           } catch (KeeperException e) {
               System.err.println("服务信息不存在! 等待服务上线........");
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
       }
   
       //当节点状态发送变化时将执行该方法(通知处理)
       @Override
       public void process(WatchedEvent event) {
           if (event.getPath().equals(node)) {
               //根据具体逻辑处理不同的事件类型,此处只关心节点的创建删除和更新
               if (event.getType() == Event.EventType.NodeCreated) {
                   System.err.println("服务上线了");
                   getServerInfo();
               } else if (event.getType() == Event.EventType.NodeDataChanged) {
                   System.err.println("服务更新了");
                   getServerInfo();
               }else if (event.getType()== Event.EventType.NodeDeleted){
                   server_ip = null;
                   server_port = 0;
                   System.err.println("服务下线了");
               }
           }
       }
   
       public void sendToServer(String text) {
           InetSocketAddress server_address = new InetSocketAddress(server_ip, server_port);
           Socket socket = new Socket();
           try {
               socket.connect(server_address);
               //System.out.println("连接服务器成功!");
               OutputStream outputStream = socket.getOutputStream();
               outputStream.write(text.getBytes());
               System.out.println("消息发送成功!");
           } catch (IOException e) {
               e.printStackTrace();
           }
           try {
               socket.close();
           } catch (IOException e) {
               e.printStackTrace();
           }
       }
   }
   

5. 打包服务端代码,该步骤可忽略,仅为了测试客户端正确性, 为了在打包时附带其全部依赖,此处借助Spring的打包插件,在pom中添加以下内容:

   		<build>
           <plugins>
               <plugin>
                   <groupId>org.springframework.boot</groupId>
                   <artifactId>spring-boot-maven-plugin</artifactId>
                   <version>1.5.6.RELEASE</version>
                   <executions>
                       <execution>
                           <goals>
                               <goal>repackage</goal>
                           </goals>
                       </execution>
                   </executions>
               </plugin>
           </plugins>
       </build>
   

   注意:Spring-boot打包插件会自动获取项目中的主函数,必须保证主函数只有一个,所以需要暂时注释客户端的主函数,最后执行maven的package,得到jar包

6. 将jar上传至虚拟机并运行

   java -jar ZookeeperTest-1.0-SNAPSHOT.jar
   

   若没有其他问题则客户端依然可以正常连接服务器发送消息;

以上便是使用Zookeeper实现服务注册和服务发现的具体步骤,在实际开发中,我们可能还会将提供的服务部署为集群,这时可将集群中的各个服务信息作为子节点注册到指定节点下,客户端监听该节点变化,获取子节点列表从而获取到服务列表,还可以在此基础上加上负载均衡算法实现对服务列表的合理访问; 如图: