18_ Redis_ Redis master-slave replication & cluster building

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 , From master to slave only .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 .（ A father can have many sons , But a son has only one father ）

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 , Cooperate with the separation of reading and writing , 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 （ colony ） footstone ∶ 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 256G, You can't use all the memory Redis Storage memory , Generally speaking , A single Redis The maximum memory used should not exceed 20G.

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

For this scenario , We can make the following Architecture ︰

Master slave copy , Read / write separation ! 80% In this case, they are all reading operations ! Master Write first ,Slave Mainly reading , Slow down the pressure on the server ! Architecture often uses

Cluster environment configuration

Only configure slave Libraries , No need to configure the main library !

127.0.0.1:6379> info replication // View the current library information
//# Replication
role:master // Information about the current library ： Default master
connected_slaves:0 // No slave
master_failover_state:no-failover
master_replid:ab08b135b40fc3d1b0a710e52776d1aa485ce1de
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

Copy 3 Configuration files , Then modify the corresponding information

• 1、 port
• 2、pid name
• 3、log File name
• 4、dump.rdb name

Modify the host configuration file ： vim redis79.conf

Modify the slave configuration file ：vim redis80.conf

Modify the slave configuration file ：vim redis81.conf

The application scenario at this time is Single machine multi cluster ： Deploy multiple servers on one server redis service

After modifying the configuration file , Start our 3 individual redis The server , You can view through the process information !

Cluster building ： One master and two subordinates

By default , Each station Redis Servers are all primary nodes ; In general, we only need to configure the slave machine !

Command build

Configure slave : Recognize the boss ！ A master （6379） Two from （6380,6381）
Configuration command ： Execute the command in the slave ：SLAVEOF 127.0.0.1 6379

The real slave master configuration should be configured in the configuration file , It's permanent , We're using commands here , Temporary

Configuration file setup

details

The host can write , The slave can't write , Only read ！ All the information and data in the host , Will be automatically saved by the slave machine !

Host write ：

The slave can only read the content ：

Test questions ：

• The host is disconnected , The slave is still connected to the host , But because only the host can write , There is no write operation after the host goes down , This is the time , If the mainframe comes back , The slave can still get the information written by the host directly !
• If you use the command line , To configure the master-slave , If the slave is restarted at this time , The slave will change back to the host ! As long as you use the command again, it becomes a slave , Immediately you get the value from the host !

Master slave replication principle ：

Slave（ Slave ） Start successfully connected to master（ host ） A... Will be sent later sync（ Sync ） command

Master Received orders , Start the background storage process , At the same time, collect all received commands for modifying the dataset , After the background process is finished ,master Will transfer Whole 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 . We can see it in the data machine !