netty集群(一)-服务注册发现

上篇文章介绍了如何搭建一个单机版本的netty聊天室：https://www.jianshu.com/p/f786c70eeccc。

一、需要解决什么问题：

当连接数超过单机的极限时，需要将netty服务扩展成集群才能够承载更多的连接数，处理更多的消息。
在网上找了下似乎并没有非常成熟标准的netty集群相关框架或中间件，于是我决定用zookeeper作为服务注册中心来实现一个简单的netty集群。

二、基于zookeeper做netty集群服务注册发现的设计思路：

关键的几个点：
1.netty服务在启动时，向zookeeper注册一个临时节点，挂载在永久父节点/netty下，节点名是当前节点的IP地址加端口，例如:192.168.1.1:7704。

2.和单点netty服务的区别是单点netty时客户端建立链接的netty地址是写死的，集群化后由注册中心zookeeper管理可用netty服务清单，客户端通过登录接口去获取可用netty服务地址，然后建立长连接。

3.当长连接断开时，重复上图过程。

三、关键部分代码

1.需要在netty应用和接口应用都引入下面三个工具类：

zookeeper发现节点工具类

package com.msgcenter.util.zookeeper;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ThreadLocalRandom;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ServiceDiscovery {
	 
    private static final Logger logger = LoggerFactory.getLogger(ServiceDiscovery.class);
 
    private CountDownLatch latch = new CountDownLatch(1);
 
    private volatile List<String> serviceAddressList = new ArrayList<>();
 
    private String registryAddress; // 注册中心的地址
 
    public ServiceDiscovery(String registryAddress) {
        this.registryAddress = registryAddress;
 
        ZooKeeper zk = connectServer();
        if (zk != null) {
            watchNode(zk);
        }
    }
 
    /**
     * 通过服务发现，获取服务提供方的地址
     * @return
     */
    public String discover() {
        String data = null;
        int size = serviceAddressList.size();
        if (size > 0) {
            if (size == 1) {  //只有一个服务提供方
                data = serviceAddressList.get(0);
                logger.info("unique service address : {}", data);
            } else {          //使用随机分配法。简单的负载均衡法
                data = serviceAddressList.get(ThreadLocalRandom.current().nextInt(size));
                logger.info("choose an address : {}", data);
            }
        }
        return data;
    }
 
    /**
     * 连接 zookeeper
     * @return
     */
    private ZooKeeper connectServer() {
 
        ZooKeeper zk = null;
        try {
            zk = new ZooKeeper(registryAddress, 2000, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getState() == Watcher.Event.KeeperState.SyncConnected) {
                        latch.countDown();
                    }
                }
            });
            latch.await();
        } catch (IOException | InterruptedException e) {
            logger.error("", e);
        }
        return zk;
    }
 
    /**
     * 获取服务地址列表
     * @param zk
     */
    private void watchNode(final ZooKeeper zk) {
 
        try {
            //获取子节点列表
            List<String> nodeList = zk.getChildren("/route", new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getType() == Event.EventType.NodeChildrenChanged) {
                        //发生子节点变化时再次调用此方法更新服务地址
                        watchNode(zk);
                    }
                }
            });
            logger.info("node data: {}", nodeList);
            this.serviceAddressList = nodeList;
        } catch (KeeperException | InterruptedException e) {
            logger.error("", e);
        }
    }
}

zookeeper注册节点工具类

package com.msgcenter.util.zookeeper;

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.ZooDefs;
import org.apache.zookeeper.ZooDefs.Ids;
import org.apache.zookeeper.ZooKeeper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ServiceRegistry {

    private static final Logger logger = LoggerFactory.getLogger(ServiceRegistry.class);
    
    private static final String ROOT_NODE = "/route";

    private CountDownLatch latch = new CountDownLatch(1);

    private String registryAddress;

    public ServiceRegistry(String registryAddress) {
        this.registryAddress = registryAddress;
    }

    public void register(String childNode) {
        if (childNode != null) {
            ZooKeeper zk = connectServer();
            if (zk != null) {
            	try {
					if (null == zk.exists(ROOT_NODE, false)) {
						createRootNode(zk);
					}
					
					
				} catch (KeeperException e) {
					e.printStackTrace();
				} catch (InterruptedException e) {
					e.printStackTrace();
				}
                createNode(zk, childNode);
            }
        }
    }

    /**
     * 连接 zookeeper 服务器
     * @return
     */
    private ZooKeeper connectServer() {
        ZooKeeper zk = null;
        try {
            zk = new ZooKeeper(registryAddress, 2000, new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getState() == Event.KeeperState.SyncConnected) {
                        latch.countDown();
                    }
                }
            });
            latch.await();
        } catch (Exception e) {
            logger.error("", e);
        }
        return zk;
    }
    
    /**
     * 创建顶级节点
     * @param zk
     * @param data
     */
    private void createRootNode(ZooKeeper zk) {
        try {
        	if (null == zk.exists(ROOT_NODE, false)) {
                String path = zk.create(ROOT_NODE, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
                logger.info("创建路由根节点 ({})", path);
        	}
        } catch (KeeperException | InterruptedException e) {
            logger.error("创建路由根节点异常:", e);
        }
    }

    /**
     * 创建子节点
     * @param zk
     * @param data
     */
    private void createNode(ZooKeeper zk, String data) {
        try {
        	String node = ROOT_NODE + "/" + data;
        	if (null == zk.exists(node, false)) {
                byte[] bytes = data.getBytes();
                String path = zk.create(node, bytes, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
                logger.info("创建节点 ({} => {})", path, data);
        	}
        } catch (KeeperException | InterruptedException e) {
            logger.error("创建节点异常:", e);
        }
    }
    
}

测试服务注册发现工具类：

package com.msgcenter.util.zookeeper;

import java.net.UnknownHostException;
import java.util.HashMap;
import java.util.Map;

import com.msgcenter.constant.WebSocketConstant;

public class ZookeeperTester {
	
	public static void main(String[] args) throws UnknownHostException, InterruptedException {
    	// 获取zookeeper注册地址
    	String registryAddress = "47.106.99.2:2181";
    	// 将本机netty服务实例注册到zookeeper
    	ServiceRegistry serviceRegistry = new ServiceRegistry(registryAddress);
    	
    	// 获取本机ip
//    	String ip = InetAddress.getLocalHost().getHostAddress();
    	String ip1 = "192.168.1.1";
    	String ip2 = "192.168.1.2";
    	String ip3 = "192.168.1.3";
    	serviceRegistry.register(ip1 + ":" + WebSocketConstant.WEB_SOCKET_PORT);
    	serviceRegistry.register(ip2 + ":" + WebSocketConstant.WEB_SOCKET_PORT);
    	serviceRegistry.register(ip3 + ":" + WebSocketConstant.WEB_SOCKET_PORT);
    	

		ServiceDiscovery serviceDiscovery = new ServiceDiscovery(registryAddress);
		Map<String, Integer> routeMap = new HashMap<String, Integer>();
		for (int i = 0; i < 10; i++) {
			String address = serviceDiscovery.discover();
			if (!routeMap.containsKey(address)) {
				routeMap.put(address, 0);
			}
			routeMap.put(address, routeMap.get(address) + 1);
		}
		System.out.println("获取10次服务命中情况:");
		for (Map.Entry<String, Integer> entry : routeMap.entrySet()) {
			System.out.println(entry.getKey() + ":" + entry.getValue());
		}
	}
	

}

2.netty应用引入上面三个工具类，启动时向zookeeper注册自己的代码如下，在netty服务启动时调用：

    /**
     * 向注册中心注册自己
     * @throws UnknownHostException 
     */
    public static void registerZK() throws UnknownHostException {
    	// 获取本机ip
    	String ip = InetAddress.getLocalHost().getHostAddress();
    	// 获取zookeeper注册地址
    	String registeyAddress = PropKit.use("zookeeper.properties").get("zk_registry_address");
    	// 将本机netty服务实例注册到zookeeper，以ip加端口作为znode名，挂载到父节点下面，成为可用服务实例列表
    	ServiceRegistry serviceRegistry = new ServiceRegistry(registeyAddress);
    	serviceRegistry.register(ip + ":" + WebSocketConstant.WEB_SOCKET_PORT);
    }

3.接口服务引入三个工具类-获取可用netty服务地址代码示例如下:

	public ResponseResult<String> getNettyServer() {
		String discoveryAddress = "47.106.99.2:2181";
		ServiceDiscovery serviceDiscovery = new ServiceDiscovery(discoveryAddress);
		String address = serviceDiscovery.discover();
		return new ResponseResult<String>(address);
	}

上述步骤解决了建立连接路由的问题，下一步还需要解决消息的路由问题：
1.点对点发送消息，如何知道这条消息存在哪个netty服务节点，需要通知哪个服务节点推送消息。
2.对群成员广播消息时，如何知道这个群的成员分布在哪些netty服务节点上。

下篇博文描述消息的路由和推送