One . What is the sentinel mechanism

Redis The sentinel of (sentinel) The system is used to manage multiple Redis The server , The system performs the following three tasks :

• monitor (Monitoring): sentry (sentinel) Will keep checking your Master and Slave Is it working properly ( heartbeat ).
• remind (Notification): When someone is being monitored Redis When something goes wrong , sentry (sentinel) Can pass API Send notifications to administrators or other applications .
• Automatic failover (Automatic failover): When one Master When not working properly , Through the voting mechanism , Elect a new master.

sentry (sentinel) As a separate executable redis-sentinel , But actually it's just a Operating in special mode Redis The server .

Two . Sentinel mode configuration

1. preparation

Prepare three virtual machines , A mainframe , Two slaves . And both realize master-slave replication （ In my last article, I wrote how to configure redis Master-slave replication of ）

2. Sentinel mode configuration

Both slaves are equipped with sentinels .

My host port number :192.168.137.68

Now configure the sentry of the first slave .（ The second slave sentry configuration mimics the first , But change the slave name , For example mymaster1 Change it to mymaster2）

2.1  modify sentinel.conf The configuration file

sentinel monitor mymaster1  192.168.137.68 6379 1

 # Master node name IP Port number The number of elections that the master server determines to be invalid requires at least 1 individual Sentinel agree!

sentinel auth-pass mymaster1  root

2.2 modify Sentinel The number of milliseconds it takes to think the server has been disconnected

sentinel down-after-milliseconds mymaster1 30  （ The original value is 30000 30 millisecond )

2.3 Configure how many slave servers synchronize the new master server at the same time

sentinel parallel-syncs mymaster1 2

2.4 Start sentinel mode

./redis-server ../sentinel.conf --sentinel &

Okay , Here, the sentry has been configured

3、 ... and . Verify sentry （ Kill the host , Slave host ）

2.5 Kill the host master

Host operation :

 see redis process :lsof -i:6379
 Kill process :kill -9  redis Process number 

2.6 Two slave machines vote ,30 After milliseconds, one of the slaves becomes the master .

  1. One of them changes from slave to host

 Check the process :lsof -i:6379 

2. Check another slave  

remarks ：

1. There is no additional password problem in master-slave switching

      Master Compared with the original configuration file, the configuration file needs to be modified in the following places

      Slave Compared with the original configuration file, the configuration file needs to be modified in the following places

2. Stop sentinel mode

 View process number :ps -aux | grep '6379'
 Kill process ： kill -9  Sentry progress number