Flink1.19高可用及选举机制

文章目录

概要

Flink1.19高可用提供了三种实现，分别是基于K8s的高可用，基于Zookeeper的高可用和本地Standalone的高可用。Flink有四个组件实现了高可用，分别是ResourceManager,dispatcher,

JobMaster和WebMonitor,其中最核心的就是他们的选举机制，本文会以resourcemanager为例进行讲解

前置知识

LeaderContender接口

凡是要实现高可用的组件都要实现这个接口

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package org.apache.flink.runtime.leaderelection;

import java.util.UUID;

/**
 * Interface which has to be implemented to take part in the leader election process of the {@link
 * LeaderElectionService}.
 */
public interface LeaderContender {

    /**
     * Callback method which is called by the {@link LeaderElectionService} upon selecting this
     * instance as the new leader. The method is called with the new leader session ID.
     *
     * @param leaderSessionID New leader session ID
     */
    void grantLeadership(UUID leaderSessionID);

    /**
     * Callback method which is called by the {@link LeaderElectionService} upon revoking the
     * leadership of a former leader. This might happen in case that multiple contenders have been
     * granted leadership.
     */
    void revokeLeadership();

    /**
     * Callback method which is called by {@link LeaderElectionService} in case of an error in the
     * service thread.
     *
     * @param exception Caught exception
     */
    void handleError(Exception exception);
}

整体架构流程

1.启动resourcemanager，第一次启动肯定会有rm的选举

2.点进start()

3.startLeaderElection（）方法会开始leader的选举

4.这里先进行了参数的检查，随后进行注册，继续往里点

5.我们先进入createLeaderElectionDriver（）方法看一下，leader是如何选举的

6.工厂类创建driver，继续点进create方法，往里看

7.可以看见leaderElectionDriverFactory有两种实现，一种是zookeeper，还有一种是k8s，我们看其中一种zookeeper的

8.继续点

public ZooKeeperLeaderElectionDriver(
            CuratorFramework curatorFramework, LeaderElectionDriver.Listener leaderElectionListener)
            throws Exception {
        this.curatorFramework = Preconditions.checkNotNull(curatorFramework);
        this.leaderElectionListener = Preconditions.checkNotNull(leaderElectionListener);

        this.leaderLatchPath =
                ZooKeeperUtils.generateLeaderLatchPath(curatorFramework.getNamespace());
        this.leaderLatch = new LeaderLatch(curatorFramework, ZooKeeperUtils.getLeaderLatchPath());
        this.treeCache =
                ZooKeeperUtils.createTreeCache(
                        curatorFramework,
                        "/",
                        new ZooKeeperLeaderElectionDriver.ConnectionInfoNodeSelector());

        treeCache
                .getListenable()
                .addListener(
                        (client, event) -> {
                            switch (event.getType()) {
                                case NODE_ADDED:
                                case NODE_UPDATED:
                                    Preconditions.checkNotNull(
                                            event.getData(),
                                            "The ZooKeeper event data must not be null.");
                                    handleChangedLeaderInformation(event.getData());
                                    break;
                                case NODE_REMOVED:
                                    Preconditions.checkNotNull(
                                            event.getData(),
                                            "The ZooKeeper event data must not be null.");
                                    handleRemovedLeaderInformation(event.getData().getPath());
                                    break;
                            }
                        });

        leaderLatch.addListener(this);
        curatorFramework.getConnectionStateListenable().addListener(listener);
        leaderLatch.start();
        treeCache.start();
    }

9.这个方法就完成了leader的选举，由于底层封装了看不见具体实现，但我们可以看到是用了一个叫Curator的框架进行实现的