netty集群(一)-服務注冊發現

上篇文章介紹了如何搭建一個單機版本的netty聊天室：https://www.jianshu.com/p/f786c70eeccc。

一、需要解決什么問題：

當連接數超過單機的極限時，需要將netty服務擴展成集群才能夠承載更多的連接數，處理更多的消息。
在網上找了下似乎並沒有非常成熟標准的netty集群相關框架或中間件，於是我決定用zookeeper作為服務注冊中心來實現一個簡單的netty集群。

二、基於zookeeper做netty集群服務注冊發現的設計思路：

關鍵的幾個點：
1.netty服務在啟動時，向zookeeper注冊一個臨時節點，掛載在永久父節點/netty下，節點名是當前節點的IP地址加端口，例如:192.168.1.1:7704。

2.和單點netty服務的區別是單點netty時客戶端建立鏈接的netty地址是寫死的，集群化后由注冊中心zookeeper管理可用netty服務清單，客戶端通過登錄接口去獲取可用netty服務地址，然后建立長連接。

3.當長連接斷開時，重復上圖過程。

三、關鍵部分代碼

1.需要在netty應用和接口應用都引入下面三個工具類：

zookeeper發現節點工具類

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; // 注冊中心的地址
 
    public ServiceDiscovery(String registryAddress) {
        this.registryAddress = registryAddress;
 
        ZooKeeper zk = connectServer();
        if (zk != null) {
            watchNode(zk);
        }
    }
 
    /**
     * 通過服務發現，獲取服務提供方的地址
     * @return
     */
    public String discover() {
        String data = null;
        int size = serviceAddressList.size();
        if (size > 0) {
            if (size == 1) {  //只有一個服務提供方
                data = serviceAddressList.get(0);
                logger.info("unique service address : {}", data);
            } else {          //使用隨機分配法。簡單的負載均衡法
                data = serviceAddressList.get(ThreadLocalRandom.current().nextInt(size));
                logger.info("choose an address : {}", data);
            }
        }
        return data;
    }
 
    /**
     * 連接 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;
    }
 
    /**
     * 獲取服務地址列表
     * @param zk
     */
    private void watchNode(final ZooKeeper zk) {
 
        try {
            //獲取子節點列表
            List<String> nodeList = zk.getChildren("/route", new Watcher() {
                @Override
                public void process(WatchedEvent event) {
                    if (event.getType() == Event.EventType.NodeChildrenChanged) {
                        //發生子節點變化時再次調用此方法更新服務地址
                        watchNode(zk);
                    }
                }
            });
            logger.info("node data: {}", nodeList);
            this.serviceAddressList = nodeList;
        } catch (KeeperException | InterruptedException e) {
            logger.error("", e);
        }
    }
}

zookeeper注冊節點工具類

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);
            }
        }
    }

    /**
     * 連接 zookeeper 服務器
     * @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;
    }
    
    /**
     * 創建頂級節點
     * @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("創建路由根節點 ({})", path);
        	}
        } catch (KeeperException | InterruptedException e) {
            logger.error("創建路由根節點異常:", e);
        }
    }

    /**
     * 創建子節點
     * @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("創建節點 ({} => {})", path, data);
        	}
        } catch (KeeperException | InterruptedException e) {
            logger.error("創建節點異常:", e);
        }
    }
    
}

測試服務注冊發現工具類：

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 {
    	// 獲取zookeeper注冊地址
    	String registryAddress = "47.106.99.2:2181";
    	// 將本機netty服務實例注冊到zookeeper
    	ServiceRegistry serviceRegistry = new ServiceRegistry(registryAddress);
    	
    	// 獲取本機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("獲取10次服務命中情況:");
		for (Map.Entry<String, Integer> entry : routeMap.entrySet()) {
			System.out.println(entry.getKey() + ":" + entry.getValue());
		}
	}
	

}

2.netty應用引入上面三個工具類，啟動時向zookeeper注冊自己的代碼如下，在netty服務啟動時調用：

    /**
     * 向注冊中心注冊自己
     * @throws UnknownHostException 
     */
    public static void registerZK() throws UnknownHostException {
    	// 獲取本機ip
    	String ip = InetAddress.getLocalHost().getHostAddress();
    	// 獲取zookeeper注冊地址
    	String registeyAddress = PropKit.use("zookeeper.properties").get("zk_registry_address");
    	// 將本機netty服務實例注冊到zookeeper，以ip加端口作為znode名，掛載到父節點下面，成為可用服務實例列表
    	ServiceRegistry serviceRegistry = new ServiceRegistry(registeyAddress);
    	serviceRegistry.register(ip + ":" + WebSocketConstant.WEB_SOCKET_PORT);
    }

3.接口服務引入三個工具類-獲取可用netty服務地址代碼示例如下:

	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);
	}

上述步驟解決了建立連接路由的問題，下一步還需要解決消息的路由問題：
1.點對點發送消息，如何知道這條消息存在哪個netty服務節點，需要通知哪個服務節點推送消息。
2.對群成員廣播消息時，如何知道這個群的成員分布在哪些netty服務節點上。

下篇博文描述消息的路由和推送