Redis（147）Redis的Cluster的容错性如何？

Redis Cluster 通过多种机制来实现高容错性，包括主从复制、自动故障转移和Gossip协议。这些机制确保即使在节点发生故障时，集群仍然能继续运行并提供服务。以下是详细的解释，并结合Java代码示例来说明其实现。

1. 主从复制（Master-Slave Replication）

主从复制是Redis Cluster最基础的高容错机制。每个主节点可以有一个或多个从节点，这些从节点复制主节点的数据。当主节点发生故障时，从节点可以接管其角色。

代码示例

import java.util.ArrayList;
import java.util.List;

class ClusterNode {
    String name;
    String ip;
    int port;
    boolean isMaster;
    ClusterNode master;

    ClusterNode(String name, String ip, int port, boolean isMaster, ClusterNode master) {
        this.name = name;
        this.ip = ip;
        this.port = port;
        this.isMaster = isMaster;
        this.master = master;
    }

    @Override
    public String toString() {
        return "Node " + name + ": " + ip + ":" + port + ", Role: " + (isMaster ? "Master" : "Slave");
    }
}

class Cluster {
    List<ClusterNode> nodes = new ArrayList<>();

    void addNode(String name, String ip, int port, boolean isMaster, ClusterNode master) {
        nodes.add(new ClusterNode(name, ip, port, isMaster, master));
    }

    void printNodes() {
        for (ClusterNode node : nodes) {
            System.out.println(node);
        }
    }
}

public class RedisClusterDemo {
    public static void main(String[] args) {
        Cluster cluster = new Cluster();

        ClusterNode master1 = new ClusterNode("master1", "192.168.1.1", 6379, true, null);
        cluster.addNode(master1.name, master1.ip, master1.port, master1.isMaster, master1.master);
        cluster.addNode("slave1", "192.168.1.2", 6379, false, master1);

        cluster.printNodes();
    }
}

2. 自动故障转移（Automatic Failover）

当主节点发生故障时，从节点会被提升为主节点。这个机制需要其他节点的协作，以保证集群的一致性和数据的完整性。

代码示例

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

class ClusterNode {
    String name;
    String ip;
    int port;
    boolean isMaster;
    ClusterNode master;
    long lastHeartbeat;
    boolean isFailed;

    ClusterNode(String name, String ip, int port, boolean isMaster, ClusterNode master) {
        this.name = name;
        this.ip = ip;
        this.port = port;
        this.isMaster = isMaster;
        this.master = master;
        this.lastHeartbeat = System.currentTimeMillis();
        this.isFailed = false;
    }

    void sendHeartbeat() {
        System.out.println("Sending heartbeat to node " + name);
        lastHeartbeat = System.currentTimeMillis();
    }

    void checkHeartbeat() {
        long now = System.currentTimeMillis();
        if (now - lastHeartbeat > 3000) { // 3 seconds timeout
            System.out.println("Node " + name + " is not responding");
            isFailed = true;
        }
    }

    @Override
    public String toString() {
        return "Node " + name + ": " + ip + ":" + port + ", Role: " + (isMaster ? "Master" : "Slave");
    }
}

class Cluster {
    List<ClusterNode> nodes = new ArrayList<>();

    void addNode(String name, String ip, int port, boolean isMaster, ClusterNode master) {
        nodes.add(new ClusterNode(name, ip, port, isMaster, master));
    }

    void handleFailover() {
        for (ClusterNode node : nodes) {
            if (node.isMaster && node.isFailed) {
                for (ClusterNode slave : nodes) {
                    if (slave.master == node) {
                        System.out.println("Failover: promoting slave node " + slave.name + " to master");
                        slave.isMaster = true;
                        slave.master = null;
                        node.isMaster = false;
                        return;
                    }
                }
            }
        }
    }

    void simulateCluster() {
        Timer timer = new Timer(true);
        TimerTask task = new TimerTask() {
            @Override
            public void run() {
                for (ClusterNode node : nodes) {
                    if (node.isMaster && !node.isFailed) {
                        node.sendHeartbeat();
                    } else {
                        node.checkHeartbeat();
                        if (node.isFailed && node.isMaster) {
                            handleFailover();
                        }
                    }
                }
            }
        };
        timer.scheduleAtFixedRate(task, 0, 1000);
    }

    void printNodes() {
        for (ClusterNode node : nodes) {
            System.out.println(node);
        }
    }
}

public class RedisClusterDemo {
    public static void main(String[] args) throws InterruptedException {
        Cluster cluster = new Cluster();

        ClusterNode master1 = new ClusterNode("master1", "192.168.1.1", 6379, true, null);
        cluster.addNode(master1.name, master1.ip, master1.port, master1.isMaster, master1.master);
        cluster.addNode("slave1", "192.168.1.2", 6379, false, master1);
        cluster.addNode("slave2", "192.168.1.3", 6379, false, master1);

        cluster.printNodes();

        cluster.simulateCluster();

        // Simulate a failure of the master after 10 seconds
        Thread.sleep(10000);
        master1.isFailed = true;

        // Keep the main thread alive to see the failover in action
        Thread.sleep(20000);
    }
}

3. Gossip 协议

Gossip 协议用于节点之间交换状态信息，确保整个集群对节点状态的一致性认识。每个节点会定期向其他节点发送和接收状态信息。

代码示例

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

class ClusterNode {
    String name;
    String ip;
    int port;
    boolean isMaster;
    ClusterNode master;
    long lastHeartbeat;
    boolean isFailed;

    ClusterNode(String name, String ip, int port, boolean isMaster, ClusterNode master) {
        this.name = name;
        this.ip = ip;
        this.port = port;
        this.isMaster = isMaster;
        this.master = master;
        this.lastHeartbeat = System.currentTimeMillis();
        this.isFailed = false;
    }

    void sendHeartbeat() {
        System.out.println("Sending heartbeat from node " + name);
        lastHeartbeat = System.currentTimeMillis();
    }

    void receiveHeartbeat() {
        System.out.println("Received heartbeat at node " + name);
        lastHeartbeat = System.currentTimeMillis();
        isFailed = false;
    }

    void checkHeartbeat() {
        long now = System.currentTimeMillis();
        if (now - lastHeartbeat > 3000) { // 3 seconds timeout
            System.out.println("Node " + name + " is not responding");
            isFailed = true;
        }
    }

    @Override
    public String toString() {
        return "Node " + name + ": " + ip + ":" + port + ", Role: " + (isMaster ? "Master" : "Slave");
    }
}

class Cluster {
    List<ClusterNode> nodes = new ArrayList<>();

    void addNode(String name, String ip, int port, boolean isMaster, ClusterNode master) {
        nodes.add(new ClusterNode(name, ip, port, isMaster, master));
    }

    void handleFailover(ClusterNode failedNode) {
        for (ClusterNode node : nodes) {
            if (node.master == failedNode && !node.isFailed) {
                System.out.println("Failover: promoting slave node " + node.name + " to master");
                node.isMaster = true;
                node.master = null;
                failedNode.isMaster = false;
                return;
            }
        }
    }

    void gossip() {
        for (ClusterNode node : nodes) {
            if (!node.isFailed) {
                for (ClusterNode peer : nodes) {
                    if (peer != node) {
                        peer.receiveHeartbeat();
                    }
                }
            } else {
                handleFailover(node);
            }
        }
    }

    void simulateCluster() {
        Timer timer = new Timer(true);
        TimerTask heartbeatTask = new TimerTask() {
            @Override
            public void run() {
                for (ClusterNode node : nodes) {
                    if (!node.isFailed) {
                        node.sendHeartbeat();
                    }
                }
            }
        };

        TimerTask gossipTask = new TimerTask() {
            @Override
            public void run() {
                gossip();
            }
        };

        timer.scheduleAtFixedRate(heartbeatTask, 0, 1000);
        timer.scheduleAtFixedRate(gossipTask, 0, 1000);
    }

    void printNodes() {
        for (ClusterNode node : nodes) {
            System.out.println(node);
        }
    }
}