Redis tutorial (9): Master-slave replication configuration example

1. Replication of Redis:

The first thing that needs to be explained here is that configuring the Master-Slave mode in Redis is really simple. I believe you can do it easily after reading this blog. Here we will list some theoretical knowledge first, and then give practical cases.

The following list clearly explains the features and advantages of Redis Replication.

1). The same Master can synchronize multiple Slaves.
2). Slave can also accept connection and synchronization requests from other Slaves, which can effectively offload the synchronization pressure of the Master. So we can think of Redis's Replication architecture as a graph structure.
3). Master Server provides services to Slaves in a non-blocking manner. So during Master-Slave synchronization, the client can still submit queries or modification requests.
4). Slave Server also completes data synchronization in a non-blocking manner. During synchronization, if a client submits a query request, Redis returns the data before synchronization.
5). In order to offload the read operation pressure of the Master, the Slave server can provide read-only operation services to the client, and the write service must still be completed by the Master. Even so, the scalability of the system has been greatly improved.
6). The Master can hand over the data saving operation to the Slaves, thus avoiding the need for an independent process in the Master to complete this operation.

2. How Replication works:

After the Slave starts and connects to the Master, it will actively send a SYNC command. Afterwards, the Master will start the background save process and collect all received commands for modifying the data set. After the background process is completed, the Master will transfer the entire database file to the Slave to complete a complete synchronization. After receiving the database file data, the Slave server saves it and loads it into memory. After that, the Master continues to transmit all the collected modification commands and new modification commands to the Slaves in sequence. The Slave will execute these data modification commands this time to achieve final data synchronization.
If the link between Master and Slave is disconnected, Slave can automatically reconnect to Master, but after the connection is successful, a full synchronization will be automatically performed.
 
3. How to configure Replication:

  See the following steps:
1). Start two Redis servers at the same time. You can consider starting two Redis servers on the same machine and monitor them separately. Different ports like 6379 and 6380.
2). Execute the command on the Slave server:

  /> redis-cli -p 6380   #这里我们假设Slave的端口号是6380
    redis 127.0.0.1:6380> slaveof 127.0.0.1 6379 #我们假设Master和Slave在同一台主机，Master的端口为6379
    OK

The above method only ensures that after executing the slaveof command, redis_6380 becomes the slave of redis_6379. Once the service (redis_6380) is restarted, they The replication relationship will be terminated.
If you want to ensure the Replication relationship between the two servers for a long time, you can make the following modifications in the configuration file of redis_6380:

    /> cd /etc/redis  #切换Redis服务器配置文件所在的目录。
    /> ls
    6379.conf  6380.conf
    /> vi 6380.conf
    将
    # slaveof <masterip> <masterport>
    改为
    slaveof 127.0.0.1 6379

Save and exit.
This ensures that the Redis_6380 service program will actively establish a Replication connection with Redis_6379 after each startup.

4. Application examples:

Here we assume that the Master-Slave has been established.

  #启动master服务器。
    [root@Stephen-PC redis]# redis-cli -p 6379
    redis 127.0.0.1:6379>
    #情况Master当前数据库中的所有Keys。
    redis 127.0.0.1:6379> flushdb
    OK
    #在Master中创建新的Keys作为测试数据。
    redis 127.0.0.1:6379> set mykey hello
    OK
    redis 127.0.0.1:6379> set mykey2 world
    OK
    #查看Master中存在哪些Keys。
    redis 127.0.0.1:6379> keys *
    1) "mykey"
    2) "mykey2"
    
    #启动slave服务器。
    [root@Stephen-PC redis]# redis-cli -p 6380
    #查看Slave中的Keys是否和Master中一致，从结果看，他们是相等的。
    redis 127.0.0.1:6380> keys *
    1) "mykey"
    2) "mykey2"
    
    #在Master中删除其中一个测试Key，并查看删除后的结果。
    redis 127.0.0.1:6379> del mykey2
    (integer) 1
    redis 127.0.0.1:6379> keys *
    1) "mykey"
    
    #在Slave中查看是否mykey2也已经在Slave中被删除。
    redis 127.0.0.1:6380> keys *
    1) "mykey"

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