zookeeper实战之服务注册与发现

zookeeper 应用场景

回顾下 zk 应用场景：

1. 数据发布与订阅
2. 服务注册与发现
3. 分布式锁
4. 分布式队列
5. master 选举
6. 配置中心
7. 命名服务
8. 负载均衡

zookeeper 实现服务注册与发现

服务注册与发现

再来看看 zk 在服务注册与发现中的应用：

代码实现逻辑：

服务注册：

public class ServiceRegister {

    private  static final String BASE_SERVICES = "/services";
    private static final String  SERVICE_NAME="/products";

    public static  void register(String address,int port) {
        try {ZooKeeper zooKeeper = new ZooKeeper("localhost:2181",5000,(watchedEvent)->{});
            Stat exists = zooKeeper.exists(BASE_SERVICES + SERVICE_NAME, false);
            if(exists==null) {zooKeeper.create(BASE_SERVICES + SERVICE_NAME,"".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            }
            String server_path = address+":"+port;
            // 创建的临时的有序节点
            // 临时的话断开连接了可以监听到, 有序节点创建代表每一个节点否则相同节点名称无法创建
            zooKeeper.create(BASE_SERVICES + SERVICE_NAME+"/child",server_path.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.EPHEMERAL_SEQUENTIAL);
            System.out.println("产品服务注册成功");
        } catch (Exception e) {e.printStackTrace();
        }
    }
}

发现服务：

    public class InitListener implements ServletContextListener {

    private  static final String BASE_SERVICES = "/services";
    private static final String  SERVICE_NAME="/products";

    private ZooKeeper zooKeeper;

    @Override
    public void contextInitialized(ServletContextEvent sce) {
        try {zooKeeper = new ZooKeeper("localhost:2181",5000,(watchedEvent)->{if(watchedEvent.getType() == Watcher.Event.EventType.NodeChildrenChanged  && watchedEvent.getPath().equals(BASE_SERVICES+SERVICE_NAME)) {updateServiceList();
                }
            });

            updateServiceList();} catch (Exception e) {e.printStackTrace();
        }

    }

    private void updateServiceList() {
       try{List<String> children = zooKeeper.getChildren(BASE_SERVICES  + SERVICE_NAME, true);
           List<String> newServerList = new ArrayList<String>();
           for(String subNode:children) {byte[] data = zooKeeper.getData(BASE_SERVICES  + SERVICE_NAME + "/" + subNode, false, null);
               String host = new String(data, "utf-8");
               System.out.println("host:"+host);
               newServerList.add(host);
           }
           // 保存注册服务的 ip 端口信息，以供远程 rpc 调用
           LoadBalance.SERVICE_LIST = newServerList;
       }catch (Exception e) {e.printStackTrace();
       }
    } 
}

public abstract class LoadBalance {
    public volatile static List<String> SERVICE_LIST;

    public abstract String choseServiceHost();}

/**
 * 随机负载均衡算法
 */
public class RamdomLoadBalance extends LoadBalance {
    @Override
    public String choseServiceHost() {
        String result = "";
        if(!CollectionUtils.isEmpty(SERVICE_LIST)) {int index = new Random().nextInt(SERVICE_LIST.size());
            result = SERVICE_LIST.get(index);
        }
        return result ;
    }
}

再讲讲几个关键点
1. 注册服务的时候需要创建临时节点, 断开连接的时候也就是服务端挂了后节点删除可监听到
2. 注册服务的时候创建的是有序节点, 一般来说相同服务都是有几台机器的, 创建顺序节点可区分多台机器的服务
3. 发现服务的一端监听服务节点的子节点，有子节点被删除了或者有新子节点创建即重新发现服务可用的机器

dubbo 中基于 zk 的服务注册与发现也是这个原理