使用Zookeeper实现集群中选择单机器执行任务并自动切换

1、需求背景

有一个集群（N台服务器），需要访问一个外部接口获取数据，但是每个时间点只需要一个机器来执行任务就行了，不需要所有服务器同时执行，因为集群共享数据库。

2、思路

通过Zookeeper选取连接序列号最小的服务器作为当前时间执行任务的机器，如果当前机器宕机，通过Zookeeper自动发现机制，重新选择新的执行机器，除非整个集群挂掉；

（当然，改思路可以让集群处理同一个任务集的不同部分，如N1处理1...N，N2处理N+1....N2等）

3、代码

//连接管理客户端
public class ZkClientManager implements Watcher,InitializingBean {
    private Logger log = LoggerFactory.getLogger(getClass());

    private final String ROOT_PATH = "/car_position";
    private final String SUB_PATH = ROOT_PATH + "/sub_system_";

    @Value("${zookeeper_address}")
    public String CONNECT_PATH = "127.0.0.1:2181";
    private Integer SESSION_TIME_OUT = 10000;

    private ZooKeeper zk = null;
    private String SELF_PATH = null;

    private boolean createRootPath(String data) throws KeeperException, InterruptedException {
        if (zk.exists(ROOT_PATH, true) == null) {
            String rootpath = zk.create(ROOT_PATH, data.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            log.info("------#创建根节点成功rootpath：" + rootpath);
        } else {
            log.info("------#根路径节点已经存在，不在重复创建");
        }
        return true;
    }

    private boolean createSubNode() throws KeeperException, InterruptedException {
        SELF_PATH = zk.create(SUB_PATH, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        log.info("------#创建当前zk节点路径成功，path=" + SELF_PATH);
        List<String> paths = zk.getChildren(ROOT_PATH, new ZkNodeWatcher(zk, SELF_PATH));
        WangKuoGpsUtil.sortAndCalcPath(SELF_PATH,paths);
        return true;
    }

    private void deletePath() {
        try {
            zk.delete(SELF_PATH, -1);
            log.info("-------#删除PATH=" + SELF_PATH);
        } catch (Exception e) {
            log.error("------#删除zk节点路径异常",e);
        }
    }

    private void releaseConn() {
        if (zk != null) {
            try {
                zk.close();
            } catch (InterruptedException e) {
                log.error("------#zookeeper关闭连接异常");
            }
        }
    }

    public void process(WatchedEvent event) {
        Event.KeeperState state = event.getState();
        Event.EventType type = event.getType();
        if (Event.KeeperState.SyncConnected == state) {
            if (Event.EventType.None == type) {
                log.info("------#成功连接上zk服务器");
            }
        } else if (Event.KeeperState.Disconnected == state) {
            log.info("------#与ZK服务器断开连接");
        } else if (Event.KeeperState.Expired == state) {
            log.info("会话失效");
        }
    }

    @Override
    public void afterPropertiesSet() throws Exception {
        log.info("------#Zookeeper连接服务器地址{}，timeout={}",CONNECT_PATH,SESSION_TIME_OUT);
        zk = new ZooKeeper(CONNECT_PATH, SESSION_TIME_OUT, this);
        log.info("------#初始化zookeeper连接成功");
        createRootPath("");
        createSubNode();
    }
}

//监听器，接收节点变更通知，收到通知后重新计算
public class ZkNodeWatcher implements Watcher {

    private Logger log = LoggerFactory.getLogger(getClass());
    private ZooKeeper zooKeeper;
    private String selfPath;

    public ZkNodeWatcher(ZooKeeper zooKeeper,String selfPath){
        this.zooKeeper = zooKeeper;
        this.selfPath =selfPath;
    }

    public void process(WatchedEvent event) {
        Event.KeeperState state = event.getState();
        Event.EventType type = event.getType();
        try {
            log.info("------#Zookeeper NodeWather,state={},type={}",state,type);
            if(Event.EventType.NodeChildrenChanged == type){
                List<String> paths = zooKeeper.getChildren(event.getPath(), this);
                WangKuoGpsUtil.sortAndCalcPath(selfPath,paths);
            }
        } catch (Exception e) {
           log.error("------#处理时间异常",e);
        }
    }
}

//对服务器在Zookeeper上的需要进行排序，并计算出当前节点的排序位
public class WangKuoGpsUtil {
    private static Logger log = LoggerFactory.getLogger(WangKuoGpsUtil.class);
     public static void sortAndCalcPath(String nodePath,List<String> paths) {
       log.info(" ------#nodePath={} 监听节点--->{} ",nodePath,JSONObject.toJSON(paths));
        Collections.sort(paths);
        GpsQueueCache.setNodeCount(paths.size());
        GpsQueueCache.setLastTime(0L);//强制从数据库中拉取
        for(int i=0;i<paths.size();i++){
            if(nodePath.contains(paths.get(i))){
                GpsQueueCache.setNodeIndex(i+1);
                break;
            }
        }
    }

//缓存当前系统状态参数，用于业务计算
public class GpsQueueCache {

    //最近一次从数据库拉取数据的时间
    private  static Long lastTime = 0L;
    //当前服务器节点顺序位
    private static Integer nodeIndex=1;
    //当前服务器节点总量,可用于计算当前服务器处理得数据片段，根据节点偏移nodeIndex划分
    private static Integer nodeCount=1;

说明：

1、客户端启动后连接Zookeeper，获取当前节点注册的序列号；

2、计算自己在集群中的当前位置；

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3、根据位置信息做自己该做的事情。

使用Zookeeper实现集群中选择单机器执行任务并自动切换

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