Redis基础：主从模式的优点和缺点

柔情只为你懂 2023-02-16 01:39 4阅读 0赞

上篇文章使用容器化的方式构建了一个一主两丛的Redis服务，这篇文章继续在此基础之上确认一下相应的优点和缺点。

# 环境构建 #

详细可参看：[https://liumiaocn.blog.csdn.net/article/details/106582498][https_liumiaocn.blog.csdn.net_article_details_106582498]  
使用一个docker-compose.yml即可拉起一主两丛的Redis，详细如下所示：

liumiaocn:redis liumiao$ cat docker-compose.yml
    version: '2'
    services:
      # redis master
      master:
        image: redis:6.0.4
        container_name: redis-master
        restart: always
        command: redis-server --port 6379 --requirepass liumiaocn@server  --appendonly yes
        ports:
          - 6379:6379
        volumes:
          - ./data:/data
    
      # redis slave 1 
      slave1:
        image: redis:6.0.4
        container_name: redis-slave-1
        restart: always
        command: redis-server --slaveof 192.168.31.242 6379 --port 6380 --requirepass liumiaocn@server --masterauth liumiaocn@server  --appendonly yes
        ports:
          - 6380:6380
        volumes:
          - ./data:/data
    
      # redis slave 2 
      slave2:
        image: redis:6.0.4
        container_name: redis-slave-2
        restart: always
        command: redis-server --slaveof 192.168.31.242 6379 --port 6381 --requirepass liumiaocn@server --masterauth liumiaocn@server  --appendonly yes
        ports:
          - 6381:6381
        volumes:
          - ./data:/data
    liumiaocn:redis liumiao$ 
    liumiaocn:redis liumiao$ docker-compose up -d
    Creating network "redis_default" with the default driver
    Creating redis-master  ... done
    Creating redis-slave-2 ... done
    Creating redis-slave-1 ... done
    liumiaocn:redis liumiao$ docker-compose ps
        Name                   Command               State                Ports              
    -----------------------------------------------------------------------------------------
    redis-master    docker-entrypoint.sh redis ...   Up      0.0.0.0:6379->6379/tcp          
    redis-slave-1   docker-entrypoint.sh redis ...   Up      6379/tcp, 0.0.0.0:6380->6380/tcp
    redis-slave-2   docker-entrypoint.sh redis ...   Up      6379/tcp, 0.0.0.0:6381->6381/tcp
    liumiaocn:redis liumiao$

# 优点：主写，从读，降低读的压力 #

liumiaocn:redis liumiao$ redis-cli -p 6379
    127.0.0.1:6379> auth liumiaocn@server
    OK
    127.0.0.1:6379> keys *
    (empty list or set)
    127.0.0.1:6379> set greeting "hello liumiao"
    OK
    127.0.0.1:6379> get greeting
    "hello liumiao"
    127.0.0.1:6379> keys *
    1) "greeting"
    127.0.0.1:6379> 
    127.0.0.1:6379> exit
    liumiaocn:redis liumiao$

Master写，Slave可读

liumiaocn:redis liumiao$ redis-cli -p 6380
    127.0.0.1:6380> auth liumiaocn@server
    OK
    127.0.0.1:6380> keys *
    1) "greeting"
    127.0.0.1:6380> get greeting
    "hello liumiao"
    127.0.0.1:6380>

liumiaocn:redis liumiao$ redis-cli -p 6381
    127.0.0.1:6381> auth liumiaocn@server
    OK
    127.0.0.1:6381> keys *
    1) "greeting"
    127.0.0.1:6381> get greeting
    "hello liumiao"
    127.0.0.1:6381>

# 缺点：Master的写的压力难以降低 #

从节点无法进行写操作

liumiaocn:redis liumiao$ redis-cli -p 6380
    127.0.0.1:6380> auth liumiaocn@server
    OK
    127.0.0.1:6380> set name "liumiao"
    (error) READONLY You can't write against a read only replica.
    127.0.0.1:6380>

注：虽然也可设定使得slave可写，但在数据的同步等方面使用上都有很多问题。主从模式最为常见的场景就是主写从读的模式，读写分离，降低读的压力。

# 优点：从节点宕机，影响较小 #

## 事前确认 ##

liumiaocn:redis liumiao$ docker ps
    CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                              NAMES
    19ed07e594b2        redis:6.0.4         "docker-entrypoint.s…"   8 minutes ago       Up 8 minutes        6379/tcp, 0.0.0.0:6381->6381/tcp   redis-slave-2
    66e84b66542e        redis:6.0.4         "docker-entrypoint.s…"   8 minutes ago       Up 8 minutes        0.0.0.0:6379->6379/tcp             redis-master
    e1bc030fc87d        redis:6.0.4         "docker-entrypoint.s…"   8 minutes ago       Up 8 minutes        6379/tcp, 0.0.0.0:6380->6380/tcp   redis-slave-1
    liumiaocn:redis liumiao$ redis-cli -p 6380
    127.0.0.1:6380> auth liumiaocn@server
    OK
    127.0.0.1:6380> keys *
    1) "greeting"
    127.0.0.1:6380> 
    127.0.0.1:6380> exit
    liumiaocn:redis liumiao$

## 模拟slave1宕机 ##

liumiaocn:redis liumiao$ docker stop redis-slave-1
    redis-slave-1
    liumiaocn:redis liumiao$ 
    liumiaocn:redis liumiao$ redis-cli -p 6380
    Could not connect to Redis at 127.0.0.1:6380: Connection refused
    not connected> exit
    liumiaocn:redis liumiao$

## 剩余一主一从仍可使用 ##

liumiaocn:redis liumiao$ redis-cli -p 6379
    127.0.0.1:6379> auth liumiaocn@server
    OK
    127.0.0.1:6379> keys *
    1) "greeting"
    127.0.0.1:6379> set version 0.1
    OK
    127.0.0.1:6379> keys *
    1) "version"
    2) "greeting"
    127.0.0.1:6379> exit
    liumiaocn:redis liumiao$ 
    liumiaocn:redis liumiao$ redis-cli -p 6381
    127.0.0.1:6381> auth liumiaocn@server
    OK
    127.0.0.1:6381> keys *
    1) "greeting"
    2) "version"
    127.0.0.1:6381> exit
    liumiaocn:redis liumiao$

## 启动slave1后即可继续使用 ##

liumiaocn:redis liumiao$ docker start redis-slave-1
    redis-slave-1
    liumiaocn:redis liumiao$ 
    liumiaocn:redis liumiao$ docker ps
    CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                              NAMES
    19ed07e594b2        redis:6.0.4         "docker-entrypoint.s…"   11 minutes ago      Up 11 minutes       6379/tcp, 0.0.0.0:6381->6381/tcp   redis-slave-2
    66e84b66542e        redis:6.0.4         "docker-entrypoint.s…"   11 minutes ago      Up 11 minutes       0.0.0.0:6379->6379/tcp             redis-master
    e1bc030fc87d        redis:6.0.4         "docker-entrypoint.s…"   11 minutes ago      Up 2 seconds        6379/tcp, 0.0.0.0:6380->6380/tcp   redis-slave-1
    liumiaocn:redis liumiao$

启动后，在宕机期间更新的数据也已经同步

liumiaocn:redis liumiao$ redis-cli -p 6380
    127.0.0.1:6380> auth liumiaocn@server
    OK
    127.0.0.1:6380> keys *
    1) "greeting"
    2) "version"
    127.0.0.1:6380> get version
    "0.1"
    127.0.0.1:6380> exit
    liumiaocn:redis liumiao$

# 缺点：主节点宕机，无法继续使用 #

liumiaocn:redis liumiao$ docker ps
    CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                              NAMES
    19ed07e594b2        redis:6.0.4         "docker-entrypoint.s…"   13 minutes ago      Up 13 minutes       6379/tcp, 0.0.0.0:6381->6381/tcp   redis-slave-2
    66e84b66542e        redis:6.0.4         "docker-entrypoint.s…"   13 minutes ago      Up 13 minutes       0.0.0.0:6379->6379/tcp             redis-master
    e1bc030fc87d        redis:6.0.4         "docker-entrypoint.s…"   13 minutes ago      Up About a minute   6379/tcp, 0.0.0.0:6380->6380/tcp   redis-slave-1
    liumiaocn:redis liumiao$ docker stop redis-master
    redis-master
    liumiaocn:redis liumiao$ docker ps
    CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                              NAMES
    19ed07e594b2        redis:6.0.4         "docker-entrypoint.s…"   13 minutes ago      Up 13 minutes       6379/tcp, 0.0.0.0:6381->6381/tcp   redis-slave-2
    e1bc030fc87d        redis:6.0.4         "docker-entrypoint.s…"   13 minutes ago      Up About a minute   6379/tcp, 0.0.0.0:6380->6380/tcp   redis-slave-1
    liumiaocn:redis liumiao$

只能连接从节点进行读操作，无法执行写操作，需要进行手工干预

liumiaocn:redis liumiao$ redis-cli -p 6380
    127.0.0.1:6380> auth liumiaocn@server
    OK
    127.0.0.1:6380> keys *
    1) "greeting"
    2) "version"
    127.0.0.1:6380> 
    127.0.0.1:6380> set name "liumiao"
    (error) READONLY You can't write against a read only replica.
    127.0.0.1:6380>

[https_liumiaocn.blog.csdn.net_article_details_106582498]: https://liumiaocn.blog.csdn.net/article/details/106582498