Redis master-slave replication

Concept

Master slave copy , It means to put one Redis Server data , Copy to other Redis The server . The former is called the main node （master/leader）, The latter is called the slave node （slave/follower）; Data replication is one-way , Only master node to slave node .Master Write first ,Slave Mainly reading .

By default , Each station Redis Servers are all primary nodes ; And a master node can have multiple slave nodes （ Or no slave ）, But a slave node can only have one master node .

The main functions of master-slave replication include

1. data redundancy ： Master-slave replication realizes hot backup of data , It's a way of data redundancy beyond persistence .
2. Fault recovery ： When there is a problem with the master node , Can be served by a slave node , Fast fault recovery ; It's actually a redundancy of services .
3. Load balancing ： On the basis of master-slave replication , Configure read-write separation , Write service can be provided by the master node , Read service provided by slave node （ The write Redis Connect master node when data is applied , read Redis Apply connection from node when data ）, Share server load ; Especially in the situation of less writing and more reading , Sharing read load through multiple slave nodes , Can be greatly improved Redis Concurrency of servers
4. High availability cornerstone ： In addition to the above functions , Master slave replication is also the foundation for sentinels and clusters to implement , So master-slave replication is Redis High availability Foundation

Generally speaking , To put Redis Used in engineering projects , Use only one Redis Absolutely not , Here's why ：

1. Structurally . Single Redis The server will have a single point of failure , And a server needs to handle all the request loads , pressure ;
2. In terms of capacity , Single Redis Server memory capacity is limited , Even if it's a Redis The memory capacity of the server is 265G, Nor can all memory be used Redis Storage memory , Generally speaking , A single Redis The maximum suitable memory should not exceed 20G

Products on e-commerce websites , It's usually a upload , Countless times , To be professional is “ Read more and write less ””.

For this scenario , We can use the following architecture ：

Environment configuration

  Basic configuration

Equipped with slave warehouse, not equipped with master warehouse , Configuration from library ：

127.0.0.1:6379> info replication                # View the current library information
# Replication                
role:master                # role   master
connected_slaves:0        # No slave
master_failover_state:no-failover
master_replid:5376842b5adf40815bebfb0c9a541f015252b7d8
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0

slaveof  Main library ip    Main library port   # Configure master and slave

info replication   # Check the information

Every time with master After disconnection , All need to be reconnected , Unless you configure it into redis.conf file

Modify the configuration file

preparation ： We configure master-slave replication , At least three... Are needed , One master and two subordinates , Configure three clients

1、 Copy multiple redis.conf file

 

 2、 Designated port 6379, By analogy

3、 Turn on daemonize  yes

4、pid File name pidfile /www/server/reids/redis_6379.pid, By analogy

5、Log File name logfile “/www/server/redis/redis_6379.log”, By analogy

6、Dump.rdb File name dbfilename dump6379.rdb, By analogy

After the above configuration is completed ,3 A service passes 33 A different configuration file opens , Our preparation Environment Bureau ok 了

  One master and two subordinates

  One master and two servants

1、 Environment initialization

 

By default, all three are Master Master node

 

 

 

2、 Configure as a Master Two Slave

 

 

 

 3、 Set the value on the host , You can get it from the slave ！ The slave cannot write values ！

 

 

Test one ： The mainframe is down , View slave information , Host recovery , Check the information again

Test two ： The slave hung up , View host information , Recover from the machine , View slave information

 

Layers of links

  the previous Slave It could be the next Slave and Master,Slave Can also receive other slaves Connection and synchronization requests for , Then the slave As the next in the chain master', Can effectively reduce master The pressure of writing ！

 

Plot to usurp the throne  

In the case of one master and two slaves , If the host is disconnected , The slave can use the command SLAVEOF NO ONE Change yourself to a host ！ At this time, other slaves are linked to this node . Execute a command on a secondary server SLAVEOF NO ONE This will cause the secondary server to turn off replication , And from the slave server back to the master server , The data set from the original synchronization will not be discarded

  The host comes back , It's just a bare pole commander , The slave runs to the new host for normal use ！

The principle of replication

Slave Start successfully connected to master A... Will be sent later sync command

Master Received orders , Start the background storage process , At the same time, collect all received commands for modifying the dataset , Execute in the background process

After finishing ,master Transfer the entire data file to slave, And complete a full synchronization .

Copy in full ： and slave The service receives the database file data , Save it and load it into memory .

Incremental replication ：Master Continue to pass all new collected modification commands to slave, Complete synchronization

But just reconnect master, One full synchronization （ Copy in full ） Will be executed automatically