集群简介

集群就是使用网络将若干台计算机联通起来，并提供统一的管理方式，使其对外呈现单机的服务效果

集群作用

分散单台服务器的访问压力，实现负载均衡
分散单台服务器的存储压力，实现可扩展性
降低单台服务器宕机带来的业务灾难

Redis集群结构设计

数据存储设计

通过算法设计，计算出key应该保存的位置
将所有的存储空间计划切割成16384份，每台主机保存一部分每份代表的是一个存储空间，不是一个key的保存空间
将key按照计算出的结果放到对应的存储空间

key通过hash算法计算出一个值，然后拿这个值%16384
得到一个数（假如是37）为key的保存位置，然后再存入相应的存储空间位置
假如又增加了一个节点，之前每个节点都会拿出部分槽给新的节点
如果是去除节点，则把被去除节点的槽加入到存在的节点当作

集群内部通讯设计

各个数据库互相通信，保存各个库中槽的编号数据

客户端发出一个key访问A，通过算法计算出key的存储位置
如果一次命中，直接返回
一次未命中，告知具体位置
一次命中或者两次命中提高数据访问效率

cluster集群结构搭建

原生安装（单条命令）
- 配置服务器（3主3从）
- 建立通信（Meet）
- 分槽（Slot）
- 搭建主从（master-slave）
工具安装（批处理）

Cluster配置

添加节点

cluster-enabled yes|no
cluster配置文件名，该文件属于自动生成，仅用于快速查找文件并查询文件内容

cluster-config-file
节点服务响应超时时间，用于判定该节点是否下线或切换为从节点

cluster-node-timeout
master连接的slave最小数量

cluster-migration-barrier

Cluster节点操作命令

查看集群节点信息
```
cluster nodes
```
进入一个从节点 redis，切换其主节点
```
cluster replicate <master-id>
```
发现一个新节点，新增主节点
```
cluster meet ip:port
```
忽略一个没有solt的节点
```
cluster forget <id>
```
手动故障转移
```
cluster failover
```
首先清空之前的数据
[root@maomao ~]# cd /usr/local/redis/data/
[root@maomao data]# ls
appendonly-6379.aof dump-6379.rdb dump.rdb
[root@maomao data]# rm -rf *

配置文件添加
cluster-enabled yes # 开启cluster
cluster-config-file nodes-6379.conf # 配置文件和名字
cluster-node-timeout 10000 # cluster下线时间，超时时间为10秒

复制六个配置文件
sed 's/6379/6380/g' redis-6379.conf > redis-6380.conf
sed 's/6379/6381/g' redis-6379.conf > redis-6381.conf
sed 's/6379/6382/g' redis-6379.conf > redis-6382.conf
sed 's/6379/6383/g' redis-6379.conf > redis-6383.conf
sed 's/6379/6384/g' redis-6379.conf > redis-6384.conf
sed 's/6379/6385/g' redis-6379.conf > redis-6385.conf
检查
cat redis-6385.conf |grep -v '#' |grep -v '^$'
开启服务
redis-server redis_config/redis-6379.conf
...
redis-server redis_config/redis-6384.conf
[root@maomao bin]# ps aux |grep redis-
root       2116  0.2  0.5 165020 10824 pts/0    Sl+  02:23   0:00 redis-server 127.0.0.1:6379 [cluster]
root       2121  0.2  0.5 165020 10664 pts/7    Sl+  02:23   0:00 redis-server 127.0.0.1:6380 [cluster]
root       2126  0.2  0.5 165020 10720 pts/6    Sl+  02:23   0:00 redis-server 127.0.0.1:6381 [cluster]
root       2131  0.2  0.6 171164 12768 pts/2    Sl+  02:23   0:00 redis-server 127.0.0.1:6382 [cluster]
root       2136  0.2  0.5 165020 10760 pts/5    Sl+  02:24   0:00 redis-server 127.0.0.1:6383 [cluster]
root       2141  0.1  0.5 165020 10788 pts/1    Sl+  02:24   0:00 redis-server 127.0.0.1:6384 [cluster]
redis-cli --cluster create 127.0.0.1:6379 127.0.0.1:6380 127.0.0.1:6381 127.0.0.1:6382 127.0.0.1:6383 127.0.0.1:6384 --cluster-replicas 1
>>> Performing hash slots allocation on 6 nodes...
Master[0] -> Slots 0 - 5460
Master[1] -> Slots 5461 - 10922
Master[2] -> Slots 10923 - 16383
Adding replica 127.0.0.1:6383 to 127.0.0.1:6379
Adding replica 127.0.0.1:6384 to 127.0.0.1:6380
Adding replica 127.0.0.1:6382 to 127.0.0.1:6381
>>> Trying to optimize slaves allocation for anti-affinity
[WARNING] Some slaves are in the same host as their master
M: 56aa54f614a2fc8f99e30a109d5e6a91d723193e 127.0.0.1:6379
   slots:[0-5460] (5461 slots) master
M: 083eb7940fb5d5444563e3a48d36a1609b8d5af4 127.0.0.1:6380
   slots:[5461-10922] (5462 slots) master
M: f515c69256533ebb17d2aabefe81d6e630f7eee5 127.0.0.1:6381
   slots:[10923-16383] (5461 slots) master
S: d25e2d50c3b6136cafc3cdd0a5fef0e86fbf66fb 127.0.0.1:6382
   replicates 56aa54f614a2fc8f99e30a109d5e6a91d723193e
S: 86f0f88285ca648df41e8f348e41cf5ef520bdae 127.0.0.1:6383
   replicates 083eb7940fb5d5444563e3a48d36a1609b8d5af4
S: 738d205c923600d6f7c8ea8df8313527b8267b95 127.0.0.1:6384
   replicates f515c69256533ebb17d2aabefe81d6e630f7eee5
Can I set the above configuration? (type 'yes' to accept): 
6379 6380 6381 是master
6382 6383 6384 是slave
slots 就是槽 三个master分的槽都一样多 平均分配
Can I set the above configuration? (type 'yes' to accept): yes
>>> Nodes configuration updated
>>> Assign a different config epoch to each node
>>> Sending CLUSTER MEET messages to join the cluster
Waiting for the cluster to join
>>> Performing Cluster Check (using node 127.0.0.1:6379)
M: 56aa54f614a2fc8f99e30a109d5e6a91d723193e 127.0.0.1:6379
   slots:[0-5460] (5461 slots) master
   1 additional replica(s)
S: d25e2d50c3b6136cafc3cdd0a5fef0e86fbf66fb 127.0.0.1:6382
   slots: (0 slots) slave
   replicates 56aa54f614a2fc8f99e30a109d5e6a91d723193e
S: 86f0f88285ca648df41e8f348e41cf5ef520bdae 127.0.0.1:6383
   slots: (0 slots) slave
   replicates 083eb7940fb5d5444563e3a48d36a1609b8d5af4
M: 083eb7940fb5d5444563e3a48d36a1609b8d5af4 127.0.0.1:6380
   slots:[5461-10922] (5462 slots) master
   1 additional replica(s)
M: f515c69256533ebb17d2aabefe81d6e630f7eee5 127.0.0.1:6381
   slots:[10923-16383] (5461 slots) master
   1 additional replica(s)
S: 738d205c923600d6f7c8ea8df8313527b8267b95 127.0.0.1:6384
   slots: (0 slots) slave
   replicates f515c69256533ebb17d2aabefe81d6e630f7eee5
[OK] All nodes agree about slots configuration.
>>> Check for open slots...
>>> Check slots coverage...
[OK] All 16384 slots covered.
可以查看日志
[root@maomao bin]# cat /usr/local/redis/data/nodes-6379.conf 
集群搭建完成
测试
[root@maomao bin]# redis-cli
127.0.0.1:6379> set name maomao
(error) MOVED 5798 127.0.0.1:6380    # 叫我们去这个槽操作
[root@maomao bin]# redis-cli -c        # 操控集群使用 redis-cli -c
127.0.0.1:6379> set name maomao
-> Redirected to slot [5798] located at 127.0.0.1:6380
OK
我们在6382获取key 失败
[root@maomao bin]# redis -cli -c -p 6382
-bash: redis: command not found
[root@maomao bin]# redis-cli -c -p 6382
127.0.0.1:6382> get name
-> Redirected to slot [5798] located at 
127.0.0.1:6380
"maomao"
127.0.0.1:6380> exit
连接到6380就能够获取key
[root@maomao bin]# redis-cli -c -p 6380
127.0.0.1:6380> get name
"maomao"

主从下线和主从切换

我们将一个主节点下线，然后查看信息
127.0.0.1:6380> cluster nodes
86f0f88285ca648df41e8f348e41cf5ef520bdae 127.0.0.1:6383@16383 slave 083eb7940fb5d5444563e3a48d36a1609b8d5af4 0 1618815771240 
2 connected
083eb7940fb5d5444563e3a48d36a1609b8d5af4 127.0.0.1:6380@16380 myself,master - 0 1618815770000 2 connected 5461-10922
56aa54f614a2fc8f99e30a109d5e6a91d723193e 127.0.0.1:6379@16379 master,fail - 1618815743184 1618815740000 1 disconnected
d25e2d50c3b6136cafc3cdd0a5fef0e86fbf66fb 127.0.0.1:6382@16382 master - 0 1618815768232 7 connected 0-5460
f515c69256533ebb17d2aabefe81d6e630f7eee5 127.0.0.1:6381@16381 master - 0 1618815770000 3 connected 10923-16383
738d205c923600d6f7c8ea8df8313527b8267b95 127.0.0.1:6384@16384 slave f515c69256533ebb17d2aabefe81d6e630f7eee5 0 1618815770238 
3 connected
master,fail意思是master会回来