Redis Cluster是Redis官方提供的分布式解决方案，通过数据分片、故障转移和自动重配置等机制，实现了高可用性和横向扩展能力。本文将深入解析Redis Cluster的核心机制，并结合实际运维场景，详细介绍常用的运维命令。

1 Redis Cluster核心机制

1.1 数据分片（Slot）

Redis Cluster将数据分布到多个节点上，通过哈希槽（Slot）的方式实现数据分片。集群总共有 16384个哈希槽，每个节点负责管理一部分槽位。

哈希槽的分配规则：

• 每个键通过CRC16算法计算出一个哈希值，然后对16384取模，得到对应的槽位编号
• 集群中的每个主节点负责一部分槽位，例如：
  • 节点A：负责槽位 0-5460
  • 节点B：负责槽位 5461-10922
  • 节点C：负责槽位 10923-16383

2 故障转移

Redis Cluster通过自动故障检测和从节点选举机制实现高可用性。

自动故障检测：

• 每个节点会定期向其他节点发送ping消息，检测其是否在线
• 如果某个主节点在指定时间内未响应，集群会将其标记为“疑似下线”
• 当大多数主节点确认该节点下线后，集群会触发故障转移

从节点选举逻辑：

• 当主节点下线后，集群会从其从节点中选举一个新的主节点
• 选举规则：

1）从节点的优先级（slave-priority）越高，越容易被选举为主节点
        2）如果优先级相同，则选择复制偏移量（replication offset）最大的从节点

• 选举完成后，集群会更新配置，并将新的主节点信息广播给所有节点

3 Redis Cluster常用运维命令

3.1 cluster nodes

# 示例
/usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@ cluster nodes[root@node4 bin]# /usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@ cluster nodes
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
034005a84845645fac6834900a11254db009ccec 192.168.10.34:6380@16380 slave bc972a8cec9c52e5c4b5da01b7674edd8f9891a5 0 1742308064559 1 connected
4297823a72a4677329764bdfbdd6fdb0f1b25182 192.168.10.34:6379@16379 master - 0 1742308063743 3 connected 5461-10922
f4aebe01a277c7384356d10dd9f14381aadba730 192.168.10.33:6380@16380 slave 72a68c3bbe6f8228640afabbd0d6100f681bfb87 0 1742308065271 5 connected
5eb12144975cb46c0cee39d63407488f7bcc99c6 192.168.10.35:6380@16380 slave 4297823a72a4677329764bdfbdd6fdb0f1b25182 0 1742308064252 3 connected
72a68c3bbe6f8228640afabbd0d6100f681bfb87 192.168.10.35:6379@16379 master - 0 1742308064764 5 connected 10923-16383
bc972a8cec9c52e5c4b5da01b7674edd8f9891a5 192.168.10.33:6379@16379 myself,master - 0 1742308064000 1 connected 0-5460 [1000->-f4aebe01a277c7384356d10dd9f14381aadba730]
[root@node4 bin]# 

3.2 cluster info

# 示例
/usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@ cluster info[root@node4 bin]# /usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@ cluster info
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
cluster_state:ok
cluster_slots_assigned:16384
cluster_slots_ok:16384
cluster_slots_pfail:0
cluster_slots_fail:0
cluster_known_nodes:6
cluster_size:3
cluster_current_epoch:7
cluster_my_epoch:1
cluster_stats_messages_ping_sent:20169
cluster_stats_messages_pong_sent:19908
cluster_stats_messages_fail_sent:10
cluster_stats_messages_sent:40087
cluster_stats_messages_ping_received:19903
cluster_stats_messages_pong_received:20158
cluster_stats_messages_meet_received:5
cluster_stats_messages_fail_received:11
cluster_stats_messages_auth-req_received:3
cluster_stats_messages_received:40080
[root@node4 bin]# 

• 输出解析：
  • cluster_state：集群状态（ok表示正常）
  • cluster_slots_assigned：已分配的槽位数
  • cluster_slots_ok：正常的槽位数
  • cluster_known_nodes：集群中已知的节点数

3.3 cluster failover

# 示例 
/usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@ cluster failover

3.4 cluster addslots

# 示例 
/usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@ cluster addslots 0 1 2 3

3.5 cluster check

/usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@--cluster check 192.168.10.33:6379[root@node4 bin]# /usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@--cluster check 192.168.10.33:6379
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
AUTH failed: WRONGPASS invalid username-password pair or user is disabled.
[root@node4 bin]# /usr/local/redis/bin/redis-cli -p 6379 -a lahmy1c@ --cluster check 192.168.10.33:6379
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
192.168.10.33:6379 (bc972a8c...) -> 1 keys | 5461 slots | 1 slaves.
192.168.10.34:6379 (4297823a...) -> 0 keys | 5462 slots | 1 slaves.
192.168.10.35:6379 (72a68c3b...) -> 0 keys | 5461 slots | 1 slaves.
[OK] 1 keys in 3 masters.
0.00 keys per slot on average.
>>> Performing Cluster Check (using node 192.168.10.33:6379)
M: bc972a8cec9c52e5c4b5da01b7674edd8f9891a5 192.168.10.33:6379slots:[0-5460] (5461 slots) master1 additional replica(s)
S: 034005a84845645fac6834900a11254db009ccec 192.168.10.34:6380slots: (0 slots) slavereplicates bc972a8cec9c52e5c4b5da01b7674edd8f9891a5
M: 4297823a72a4677329764bdfbdd6fdb0f1b25182 192.168.10.34:6379slots:[5461-10922] (5462 slots) master1 additional replica(s)
S: f4aebe01a277c7384356d10dd9f14381aadba730 192.168.10.33:6380slots: (0 slots) slavereplicates 72a68c3bbe6f8228640afabbd0d6100f681bfb87
S: 5eb12144975cb46c0cee39d63407488f7bcc99c6 192.168.10.35:6380slots: (0 slots) slavereplicates 4297823a72a4677329764bdfbdd6fdb0f1b25182
M: 72a68c3bbe6f8228640afabbd0d6100f681bfb87 192.168.10.35:6379slots:[10923-16383] (5461 slots) master1 additional replica(s)
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
[WARNING] Node 192.168.10.33:6379 has slots in migrating state 1000.
[WARNING] The following slots are open: 1000.
>>> Check slots coverage...
[OK] All 16384 slots covered.
[root@node4 bin]# 

4 总结

Redis Cluster通过数据分片和故障转移机制，实现了高可用性和横向扩展能力。掌握集群的核心机制和常用运维命令，可以帮助你更好地管理和维护Redis集群。在实际运维中，建议定期检查集群状态，及时处理故障，并根据业务需求调整集群规模。