leader选举

09 Feb 2018

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最近在项目中使用了zk来实现主节点的选举，下面主要介绍下curator中提供的leader selector模块

Apache Curator

Apache Curator是Apache提供的zookeeper客户端，提供了诸如zk节点操作，分布式锁，通知，订阅，注册发现选举等操作。

选举客户端

继承LeaderSelectorListenerAdapter，实现LeaderSelectorListenerAdapter#takeLeadership方法，该方法由curator框架负责在当前客户端节点成为leader之后回调。

需要注意，LeaderSelectorListenerAdapter#takeLeadership方法推出则代表当前节点归还leader权限，当你希望该节点长期持有leader权限时，请不要退出该方法。

leaderSelector.autoRequeue()会在当前节点归还了leader权限后，重新将当前节点竞选队列。

简单的java案例：

public class SelectorClient extends LeaderSelectorListenerAdapter implements Closeable{

    private final LeaderSelector leaderSelector;
    private final String selectorPath = "/selector/leader";

    private boolean leader = false;
    private int waitSecond = 5;

    @Autowired
    public SelectorClient(CuratorFramework curatorFramework) {
        this.leaderSelector = new LeaderSelector(curatorFramework, selectorPath, this);
        this.leaderSelector.autoRequeue();
    }

    @Override
    public void takeLeadership(CuratorFramework curatorFramework) throws Exception {
        leader = true;
        try {
            TimeUnit.SECONDS.sleep(waitSecond);
        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            leader = false;
        }
    }

    @Override
    public void close() throws IOException {
        this.leaderSelector.close();
    }

    public void start() {
        this.leaderSelector.start();
    }

    public boolean isLeader() {
        return leader;
    }

    public void giveBack() {
        this.leaderSelector.requeue();
    }

}

启动选举

启动curator框架：CuratorFramework.start()
启动使用第一步CuratorFramework构建的SelectorClient：selector.start()