Redis sentinel mechanism and configuration

One 、 Why? Redis There should be sentinel mechanism in the cluster

Redis Master slave replication has one drawback , When master After the outage , The whole cluster will hang up . because redis Itself will not automatically from slave To elect a new master Of .

Our ideal situation is ： When master After hanging up , There can be slave Fill in quickly , Automatically switch to master, It does not affect the whole service .

Based on this , Introduced Redis Sentinel（Redis Sentinel mechanism ）.

It can be master After hanging up , Automatically from More than one slave In the election of new master, Start working quickly , It saves the trouble of manual switching , Realized redis High availability .

Two 、 After the analog host hangs , Manual switching

1、 Introduction to the environment

Here are four redis, Respectively the ip yes ：

master：172.10.0.2

slave1：172.10.0.3
slave2：172.10.0.4
slave3：172.10.0.5

　

2、 The original master Hang up

adopt  netstat -anp|grep 6379  Command found master Of pid, then kill fall .

Go to a few slave Query in  info replication, Will find ,master It's already  down.

　

3、 Manually put a slave The election became the new master

　
choice slave2 Become new master：

（1） Go to slave2 Client execution  slave no one command

The order will slave2 And the original master The master-slave relationship is broken , Make yourself... Again master（ Of course , This master There is no one slave ）

（2） To the other two slave perform  slaveof 172.10.0.4 6379  Or configuration slaveof

Be careful requirepass、masterauth、bind Configuration of , And restart 、 Reload the configuration file , Otherwise it may not work .

Although manual mode can also realize switching , But it is inevitable to encounter

‘ Which one is elected for  master’,

‘ If it breaks again, it has to be reconfigured ’,

‘ If something else is delayed , Didn't have time to configure , Will be unable to provide services for a long time ’ Other questions ,

therefore , The sentinel mechanism becomes very necessary .

3、 ... and 、 The principle of the sentry mechanism

Redis Sentinel Is a distributed architecture , There are several Sentinel Nodes and Redis Data nodes , Every Sentinel The node will Sentinel Node monitoring , When it finds that the node is not reachable , The node will be marked as offline .

Sentinels gather to monitor redis Whether the master and slave operate normally .

If the slave node hangs , Then the sentinel assembly will make this slave node offline identification ;

If it's the master node that's down , Then the sentinel set will not only make offline identification for the main node , And it will be carried out by all sentinels " negotiation ”, Elect a new master node , To complete automatic failover . After the original primary node returns to normal , The slave node that will become the new master node .

The whole process is completely automatic , No need for manual access .

Four 、 The realization of sentry mechanism

1、 Create three redis-sentinel, Form a sentinel collection

docker run -itd --name  redis-sentinel-1 --privileged  --net haveyb-network  -p 6384:6379  --ip 172.10.0.6  docker-test

docker run -itd --name  redis-sentinel-2 --privileged  --net haveyb-network  -p 6385:6379  --ip 172.10.0.7  docker-test

docker run -itd --name  redis-sentinel-3 --privileged  --net haveyb-network  -p 6386:6379  --ip 172.10.0.8  docker-test

notes ：--net haveyb-network Specify a custom network for

2、 Use  docker ps -a  Command to view the currently created container

3、 Enter the three newly created sentinel Every container of

docker exec -it redis-sentinel-3 bash

4、 modify net.core.somaxconn Value

vi /etc/sysctl.conf 

（1） Add the following line of code ：

net.core.somaxconn = 32768

（2） load

sysctl -p

5、 modify redis.conf

vi /etc/redis.conf

（1） Modify the parameters bind 127.0.0.1 by 0.0.0.0

bind 0.0.0.0

（2） Set up redis password

requirepass YourPasswordSettings

（3） Load profile

redis-server /etc/redis.conf &

6、 Modify the new three redis-sentinel Of redis-sentinel.conf

vi /etc/redis-sentinel.conf

（1） modify # bind 127.0.0.1 192.168.1.1 by bind 0.0.0.0

bind 0.0.0.0

（2） Delete this line of code

sentinel monitor mymaster 127.0.0.1 6379 2

This line of code is redis By default （ Nothing commented out ）, We will configure it later , So just delete it , It will also avoid problems caused by sequence .

（3） Add the following code

sentinel monitor mymaster 172.10.0.2 6379 2

sentinel auth-pass mymaster yourPasswordSettings

sentinel down-after-milliseconds mymaster 3000

explain ：

First line of code ：

The name of the master node monitored （ Can start at will , This is called master）、IP And port , the last one 2 There are several Sentinel Find a problem , Perform failover . Generally, this number is set to Sentinel Half of the number of nodes plus 1.

However, it is suggested that the name be mymaster（ The default is this ）, Because if you call it another name , There are several corresponding changes needed .

Second line of code ：

Fill in the connection master Your name and password , The default name is used here mymaster, The password should be filled in master Password , I have set it the same here .

Third line of code

Is to set how often the heartbeat is detected , This is set to 3 second

7、 Newly built in three stations respectively redis-sentinel Load the sentry configuration file

redis-sentinel /etc/redis-sentinel.conf &

8、 Verify that the configuration is successful

If something similar to the following figure appears , It means that the sentry configuration is successful

notes ： Remove a sentinel pair master Monitoring of , Carry out orders in the sentry

sentinel remove mastername