Redis（140）Redis的Cluster的故障转移是如何实现的？

Redis Cluster 的故障转移机制确保在主节点（Master）出现故障时，集群中的从节点（Slave）能够自动接管主节点的角色，从而保证高可用性。故障转移的实现涉及节点状态监控、故障检测、选举新主节点及更新集群状态等步骤。下面我们详细解析这些步骤，并结合代码示例进行深入探讨。

1. 节点状态监控和故障检测

每个 Redis 集群节点都会定期向其他节点发送 PING 消息，并期望收到 PONG 回复。如果在一定时间内未收到回复，该节点将认为目标节点可能失效。

代码示例

1/* Cluster node structure */
2typedef struct clusterNode {
3    char name[40];      /* Node ID */
4    int flags;          /* Node flags: master, slave, fail, etc. */
5    mstime_t ping_sent; /* Last time a ping was sent */
6    mstime_t pong_received; /* Last time a pong was received */
7    // other fields...
8} clusterNode;
9
10/* Function to check for node failures */
11void clusterCron(void) {
12    mstime_t now = mstime();
13    dictIterator *di;
14    dictEntry *de;
15
16    di = dictGetSafeIterator(server.cluster->nodes);
17    while((de = dictNext(di)) != NULL) {
18        clusterNode *node = dictGetVal(de);
19
20        if (node->flags & CLUSTER_NODE_MYSELF) continue;
21
22        if (now - node->pong_received > server.cluster_node_timeout) {
23            // Mark the node as failing
24            node->flags |= CLUSTER_NODE_PFAIL;
25            printf("Node %s is in PFAIL state\n", node->name);
26        }
27    }
28    dictReleaseIterator(di);
29}
30

2. 故障确认和投票

当一个节点被标记为 PFAIL（疑似失败）状态后，如果多数主节点（Master）也标记该节点为 FAIL（确定失败）状态，那么该节点将被认为真的失效。

代码示例

1/* Function to confirm node failure */
2void clusterSendFail(clusterNode *node) {
3    dictIterator *di;
4    dictEntry *de;
5
6    di = dictGetSafeIterator(server.cluster->nodes);
7    while ((de = dictNext(di)) != NULL) {
8        clusterNode *peer = dictGetVal(de);
9
10        if (peer->flags & CLUSTER_NODE_MYSELF) continue;
11
12        // Send FAIL message to other nodes
13        clusterSendMessage(peer, node, CLUSTERMSG_TYPE_FAIL);
14    }
15    dictReleaseIterator(di);
16}
17
18/* Function to process FAIL messages */
19void clusterProcessFail(clusterMsg *msg) {
20    clusterNode *node = clusterLookupNode(msg->data.fail.nodeid);
21
22    if (node == NULL) return;
23
24    // Mark the node as FAIL
25    node->flags |= CLUSTER_NODE_FAIL;
26    printf("Node %s marked as FAIL\n", node->name);
27}
28

3. 选举新的主节点

当主节点被确定为失效后，其从节点将参与选举。参与选举的从节点会向其他主节点发送投票请求，并根据收到的投票数量决定是否成为新的主节点。

代码示例

1/* Function to initiate failover */
2void clusterHandleSlaveFailover(clusterNode *slave) {
3    if (!(slave->flags & CLUSTER_NODE_SLAVE)) return;
4
5    // Promote the slave to master
6    slave->flags &= ~CLUSTER_NODE_SLAVE;
7    slave->flags |= CLUSTER_NODE_MASTER;
8
9    // Send update to the cluster
10    clusterBroadcastSlaveOf(slave, NULL);
11    printf("Slave %s promoted to master\n", slave->name);
12}
13
14/* Function to broadcast SLAVEOF message */
15void clusterBroadcastSlaveOf(clusterNode *node, clusterNode *master) {
16    dictIterator *di;
17    dictEntry *de;
18
19    di = dictGetSafeIterator(server.cluster->nodes);
20    while ((de = dictNext(di)) != NULL) {
21        clusterNode *peer = dictGetVal(de);
22
23        if (peer->flags & CLUSTER_NODE_MYSELF) continue;
24
25        clusterSendMessage(peer, node, CLUSTERMSG_TYPE_SLAVEOF, master);
26    }
27    dictReleaseIterator(di);
28}
29
30/* Function to process SLAVEOF messages */
31void clusterProcessSlaveOf(clusterMsg *msg) {
32    clusterNode *node = clusterLookupNode(msg->data.slaveof.nodeid);
33
34    if (node == NULL) return;
35
36    // Update the node's master
37    node->slaveof = clusterLookupNode(msg->data.slaveof.masterid);
38    printf("Node %s updated to follow master %s\n", node->name, node->slaveof->name);
39}
40

4. 更新集群状态

一旦新的主节点被选定，集群中所有节点需要更新自己的状态信息，以便正确地处理客户端请求。

代码示例

1/* Function to update cluster state */
2void clusterUpdateState(void) {
3    dictIterator *di;
4    dictEntry *de;
5
6    di = dictGetSafeIterator(server.cluster->nodes);
7    while((de = dictNext(di)) != NULL) {
8        clusterNode *node = dictGetVal(de);
9
10        if (node->flags & CLUSTER_NODE_MASTER) {
11            // Update master's state
12        } else if (node->flags & CLUSTER_NODE_SLAVE) {
13            // Update slave's state
14        }
15    }
16    dictReleaseIterator(di);
17}
18

综合示例

以下是一个综合性的代码示例，展示了 Redis Cluster 故障转移的完整流程。

1#include <stdio.h>
2#include <string.h>
3#include <stdint.h>
4#include <time.h>
5#include "crc16.h"  // Assume crc16.h provides crc16 function
6#include "dict.h"   // Assume dict.h provides a dictionary implementation
7#include "mstime.h" // Assume mstime.h provides mstime function
8
9#define CLUSTER_NODE_TIMEOUT 15000  // 15 seconds
10#define CLUSTER_NODE_MYSELF 0x01
11#define CLUSTER_NODE_MASTER 0x02
12#define CLUSTER_NODE_SLAVE 0x04
13#define CLUSTER_NODE_PFAIL 0x08
14#define CLUSTER_NODE_FAIL  0x10
15
16typedef struct clusterNode {
17    char name[40];      /* Node ID */
18    int flags;          /* Node flags: master, slave, fail, etc. */
19    mstime_t ping_sent; /* Last time a ping was sent */
20    mstime_t pong_received; /* Last time a pong was received */
21    struct clusterNode *slaveof; /* Master of this node if it's a slave */
22    // other fields...
23} clusterNode;
24
25typedef struct clusterState {
26    dict *nodes;        /* All known nodes in the cluster */
27} clusterState;
28
29clusterState *server.cluster;
30
31/* Function to hash a key to a slot */
32unsigned int keyHashSlot(char *key, int keylen) {
33    return crc16(key, keylen) & 16383;
34}
35
36/* Function to send a message to a node */
37void clusterSendMessage(clusterNode *node, const char *msg) {
38    // In a real implementation, this would send the message over a network
39    printf("Sending message to node %s: %s\n", node->name, msg);
40}
41
42/* Function to check for node failures */
43void clusterCron(void) {
44    mstime_t now = mstime();
45    dictIterator *di;
46    dictEntry *de;
47
48    di = dictGetSafeIterator(server.cluster->nodes);
49    while((de = dictNext(di)) != NULL) {
50        clusterNode *node = dictGetVal(de);
51
52        if (node->flags & CLUSTER_NODE_MYSELF) continue;
53
54        if (now - node->pong_received > CLUSTER_NODE_TIMEOUT) {
55            // Mark the node as failing
56            node->flags |= CLUSTER_NODE_PFAIL;
57            printf("Node %s is in PFAIL state\n", node->name);
58        }
59    }
60    dictReleaseIterator(di);
61}
62
63/* Function to confirm node failure */
64void clusterSendFail(clusterNode *node) {
65    dictIterator *di;
66    dictEntry *de;
67
68    di = dictGetSafeIterator(server.cluster->nodes);
69    while ((de = dictNext(di)) != NULL) {
70        clusterNode *peer = dictGetVal(de);
71
72        if (peer->flags & CLUSTER_NODE_MYSELF) continue;
73
74        // Send FAIL message to other nodes
75        clusterSendMessage(peer, "FAIL");
76    }
77    dictReleaseIterator(di);
78}
79
80/* Function to process FAIL messages */
81void clusterProcessFail(clusterMsg *msg) {
82    clusterNode *node = clusterLookupNode(msg->data.fail.nodeid);
83
84    if (node == NULL) return;
85
86    // Mark the node as FAIL
87    node->flags |= CLUSTER_NODE_FAIL;
88    printf("Node %s marked as FAIL\n", node->name);
89}
90
91/* Function to initiate failover */
92void clusterHandleSlaveFailover(clusterNode *slave) {
93    if (!(slave->flags & CLUSTER_NODE_SLAVE)) return;
94
95    // Promote the slave to master
96    slave->flags &= ~CLUSTER_NODE_SLAVE;
97    slave->flags |= CLUSTER_NODE_MASTER;
98
99    // Send update to the cluster
100    clusterBroadcastSlaveOf(slave, NULL);
101    printf("Slave %s promoted to master\n", slave->name);
102}
103
104/* Function to broadcast SLAVEOF message */
105void clusterBroadcastSlaveOf(clusterNode *node, clusterNode *master) {
106    dictIterator *di;
107    dictEntry *de;
108
109    di = dictGetSafeIterator(server.cluster->nodes);
110

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