Redis cluster concept

1.1 The concept of cluster

 

The so-called cluster , By adding the number of servers , Provide the same service , So that the server can achieve a stable 、 Efficient state .

 

1.1.1 Use redis The need for clustering

problem ： We've already deployed redis, And can start a redis, Read and write data , Why study redis colony ？

 

answer ：（1） Single redis There is instability . When redis The service is down , There is no service available .

 

（2） Single redis My reading and writing ability is limited .

 

summary ：redis Clustering is to strengthen redis The ability to read and write .

 

1.1.2 How to learn redis colony

-- explain ：（1）redis In the cluster , every last redis Call it a node .

 

      （2）redis In the cluster , There are two types of nodes ： Master node (master)、 From the node (slave).

 

      （3）redis colony , Is based on redis Master slave replication implementation .

 

                         

 

therefore , Study redis colony , It's about learning redis The master starts with copying the model .

 

1 redis Master slave copy

1.1 Concept

    Master slave replication model , There are many. redis node .

 

    among , There is and only one master node Master. From the node Slave There can be multiple .

 

 

 

As long as the network connection is normal ,Master Will always synchronize their data updates to Slaves, Keep the master and slave in sync .

 

 

 

 

1.1 characteristic

（1） Master node Master Can be read 、 Can write .

 

（2） From the node Slave read-only .（read-only）

 

 

 

therefore , The master-slave model can improve the ability of reading , It eases the ability of writing to a certain extent . Because the only way to write is Master A node , All read operations can be handed over to the slave node , In disguise, it improves the ability of writing .

 

 

 

1.1 Configuration based implementation

1.1.1 demand

Master node

 

6380

 

From the node （ Two ）

 

6381、6382

 

 

 

1.1.2 Configuration steps

（1） stay /usr/local Under the table of contents , Create a /redis/master-slave Catalog

 

[[email protected] local]# mkdir -p redis/master-slave

 

 

 

（2） stay master-slave Under the table of contents , Create three subdirectories 6380、6381、6382

 

[[email protected] master-slave]# mkdir 6380 6381 6382

 

 

 

（3） Copy in turn redis Extract... From the directory redis.conf The configuration file , Into these three subdirectories .

 

[[email protected] master-slave]# cp /root/redis-3.2.9/redis.conf ./6380/

 

[[email protected] master-slave]# cp /root/redis-3.2.9/redis.conf ./6381/

 

[[email protected] master-slave]# cp /root/redis-3.2.9/redis.conf ./6382/

 

 

 

（4） Get into 6380 Catalog , modify redis.conf, take port Change the port to 6380 that will do .

 

[[email protected] master-slave]# cd ./6380

 

[[email protected] 6380]# vim redis.conf

 

 

 

 

 

 

 

（5） Get into 6381 Catalog , modify redis.conf, take port Port changed to 6381, At the same time, specify to turn on master-slave replication .

 

[[email protected] 6380]# cd ../6381

 

[[email protected] 6381]# vim redis.conf

 

 

 

 

 

 

 

 

 

（6） Get into 6382 Catalog , modify redis.conf, take port Port changed to 6382, At the same time, specify to turn on master-slave replication .

 

[[email protected] 6380]# cd ../6382

 

[[email protected] 6381]# vim redis.conf

 

 

 

 

 

 

 

 

 

1.1.1 test

（1） Open three xshell window , In every window , Start a redis node . View log output .（ Don't start in background mode , Can't see the log , Is not intuitive ）

 

[[email protected] master-slave]# cd 6380 && redis-server ./redis.conf

 

 

 

[[email protected] master-slave]# cd 6381 && redis-server ./redis.conf

 

 

 

[[email protected] master-slave]# cd 6382 && redis-server ./redis.conf

 

 

 

 

 

 

 

（2） Open three more xshell window , In every window , Log on to a redis node

 

[[email protected] ~]# redis-cli -p 6380

 

 

 

[[email protected] ~]# redis-cli -p 6381

 

 

 

[[email protected] ~]# redis-cli -p 6382

 

 

 

（3） At the main node 6380 On , Read and write , Successful operation

 

[[email protected] ~]# redis-cli -p 6380

 

127.0.0.1:6380> set user:name zs

 

OK

 

127.0.0.1:6380> get user:name

 

"zs"

 

127.0.0.1:6380>

 

 

 

（4） At the slave node 6381 On

 

Read operation executed successfully , And succeed from 6380 The data is synchronized on the Internet

 

[[email protected] ~]# redis-cli -p 6381

 

127.0.0.1:6381> get user:name

 

"zs"

 

 

 

Write operation failed .（ From the node , Only read , Can't write ）

 

127.0.0.1:6381> set user:age 18

 

(error) READONLY You can't write against a read only slave.

 

 

 

 

 

1 Sentinel Sentinel mode

1.1 The defect of master-slave mode

When the primary node goes down , There are no writable nodes in the whole cluster .

 

 

 

Since all the data of the master node is backed up from the slave node , When the primary node goes down , If you can turn a slave node into a master node , Is it possible to solve this problem ？

 

 

 

answer ： Yes , This is Sentinel The role of a sentry .

 

 

 

1.2 The task of the sentry

Redis Of Sentinel The system is used to manage multiple Redis The server （instance）, The system performs the following three tasks ：

 

monitor （Monitoring）： Sentinel Constantly check whether your master and slave servers are working properly .

 

remind （Notification）： When someone is being monitored Redis When there's a problem with the server , Sentinel Can pass API Send notifications to administrators or other applications .

 

Automatic failover （Automatic failover）： When a primary server doesn't work , Sentinel An automatic failover operation will start , It's going to vote , Upgrade one of the slave servers to a new master server , And let the other slave servers of the failed master server copy the new master server ; When a client tries to connect to a failed primary server , The cluster will also return the address of the new primary server to the client , So that the cluster can use the new master server instead of the failed server .

 

 

 

1.2.1 monitor （Monitoring）

（1）Sentinel Can monitor any number of Master And the Master Under the Slaves.（ That is, multiple master-slave modes ）

 

（2） Under the same sentry 、 Different master-slave models , They are independent of each other .

 

（3）Sentinel Will keep checking Master and Slaves If there is something wrong .

 

 

 

 

 

 

1.2.2 Automatic failover （Automatic failover）

1.2.2.1 Sentinel The Internet

Monitor the same Master Of Sentinel Will automatically connect , Make up a distributed Sentinel The Internet , Communicate with each other and exchange information about the monitored server . The following figure , Three monitors s1 Of Sentinel, Automatically compose Sentinel Network structure .

 

 

 

 

doubt ： Why use sentinel What about the Internet ？

 

answer ： When there is only one sentinel When , If this sentinel Hang up , Then automatic failover is not possible .

 

 

 

stay sentinel In the network , As long as there is one more sentinel Alive , You can failover .

 

1.1.1.1 The process of fail over

（1） vote （ The principle of half ）

 

When any one Sentinel Find out what's being monitored Master When offline , Will inform others Sentinel The meeting , To vote for Master Are you offline （ More than half , therefore sentinel Usually with an odd number ）.

 

 

 

（2） The election

 

When Sentinel determine Master After offline , Will be in all Slaves in , Elect a new node , Upgrade to Master node .

 

Other Slaves node , To the slave node of this node .

 

  

 

 

 

 

 

 

 

         （1） vote （2） The election

 

 

 

（3） primary Master Back online

 

When the original Master After the node is online again , Automatically change to current Master The slave node of the node .

 

 

 

 

 

 

 

（3） primary master Back online

 

1.1 Sentinel mode deployment

1.1.1 demand

Premise ： There is already a running master-slave mode .

 

 

 

in addition , Configure three Sentinel example , Monitor the same Master node .

 

 

 

1.1.2 To configure Sentinel

（1） stay /usr/local Under the table of contents , establish /redis/sentinels/ Catalog

 

[[email protected] local]# mkdir -p redis/sentinels

 

 

 

（2） stay /sentinels Under the table of contents , To create s1、s2、s3 In three subdirectories

 

[[email protected] sentinels]# mkdir s1 s2 s3

 

 

 

（3） Copy in turn redis Extract... From the directory sentinel.conf file , Into these three subdirectories

 

[[email protected] sentinels]# cp /root/redis-3.2.9/sentinel.conf ./s1/

 

[[email protected] sentinels]# cp /root/redis-3.2.9/sentinel.conf ./s2/

 

[[email protected] sentinels]# cp /root/redis-3.2.9/sentinel.conf ./s3/

 

 

 

（4） Modify in turn s1、s2、s3 In subdirectories sentinel.conf file , Modify the port , And specify the master node to monitor .（ The slave node does not need to specify ,sentinel Will automatically identify ）

 

 

 

S1 The sentries are as follows ：

 

 

 

 

 

 

 

 

S2 The sentries are as follows ：

 

 

 

 

 

 

 

 

S3 The sentries are as follows ：

 

 

 

 

（5） Open three more xshell window , In every window , Start a sentinel instance , And watch the log output

 

[[email protected] sentinels]# redis-sentinel ./s1/sentinel.conf

 

 

 

[[email protected] sentinels]# redis-sentinel ./s2/sentinel.conf

 

 

 

[[email protected] sentinels]# redis-sentinel ./s3/sentinel.conf

 

 

 

Core log output ：

 

 

 

 

1.1.3 test

（1） Shut down first 6380 node . Find out , It does reassign a master node

 

 

 

 

 

 

（2） Back online 6380 node . Find out ,6380 The node becomes the slave of the new master .