Redis sentinel mode

summary

The method of master-slave switching technology is ： When the primary server goes down , You need to manually switch a server to the primary server , This requires human intervention , Laborious and arduous , It will also make the service unavailable for a period of time . This is not a way of pushing , More time , We prioritize sentinel mode .Redis from 2.8 It began to officially offer Sentinel( sentry ) Architecture to solve this problem .

Automatic version of usurpation of power , First Redis The order of the sentry , Sentinels are an independent process , As a process , He will run independently , The principle is that the sentry sends orders , wait for Reids Server response , So as to monitor the operation of multiple Redis example .

The Sentinels here have two functions

• By sending commands , Give Way Redis The server returns to monitor its running state , Including the master and slave servers
• When the sentry monitors and sweeps master Downtime , Will automatically slave Switch to master, And then through Publish subscribe mode   Notify other slave servers , Modify the configuration file , Let them switch hosts .

But a sentinel process is right Redis The server monitors , There may be problems , So , We can use multiple sentinels to monitor . There will be surveillance between the Sentinels , In this way, the multi sentry mode is formed .

Suppose the primary server goes down , sentry 1 First detect the result , The system doesn't work right away failover The process , Just sentinels 1 Subjectively, the primary server is not available , This phenomenon is called Subjective offline  . When the rear sentry also detects that the primary server is not available , And when the quantity reaches a certain value , Then there will be a vote between the Sentinels , The result of the vote was initiated by a sentinel , Conduct failover[ Fail over ] operation . After switching successfully , Through the publish and subscribe mode , Let each sentry switch the host from the server that they monitor , This process is called Objective offline .

Configuration testing

1、 Adjustment structure ,6379 With 80、81

2、 Self defined /wyt  New under the directory sentinel.conf file , The name must not be wrong

3、 Deploy sentinels , Fill in the content

• sentinel monitor The name of the monitored host  127.0.0.1 6379 1se 1
• The last number above 1, After the host is hung up slave Vote to see who takes over as the host , How many tickets to become the host

4、 Activate the sentry

• Redis-sentinel /wyt/sentinel.conf
• The above directories are configured according to their actual situation , Maybe the directory is different

5、 Normal master-slave demonstration   

6、 The original Master Hang up

7、 Vote for the new election

8、 Start again from the master and slave ,info replication Check it out

9、 problem ： If the previous master Restart back , Will it be double master Conflict ？ I can only be a little brother when I come back before

Problems you may encounter during startup

-bash: redis-sentinel: command not found
# A global command is missing , take /redis/src The executable file under the directory creates a soft connection value path in the environment variable , It's easy for the system to identify , It's like a shortcut

ln -s /www/server/redis/src/* /usr/local/bin/

If Master The node is disconnected , At this time, a server will be randomly selected from the slave machine  

  Sentinel log

If the host comes back at this time , Can only merge under the new host , As a slave , That's the rule of sentinel mode

The advantages and disadvantages of sentinel mode

         advantage

1. The sentry cluster model is based on the master-slave model , All the advantages of master-slave , Sentinel mode also has .
2. Master slave can switch , Faults can be transferred , Better system availability
3. Sentry mode is an upgrade of master-slave mode , More robust system , Higher availability .

        shortcoming

1.  Redis Difficult to support online capacity expansion , When the cluster capacity reaches the upper limit, online capacity expansion will become very complex .
2. The sentinel configuration mode is not simple , It's even a little cumbersome

Sentry configuration description

#Example sentinel.conf

# sentry sentinel The port on which the instance runs Default 26379

port 26379

# sentry sentinel Working directory of

dir /tmp

# sentry sentinel Monitored redis The master node ip port

#master-name The name of the master node that you can command yourself   There can only be letters A-z、 Numbers 0-9, These three characters “. - _” form .

#quorum How many sentinel The Sentinels agreed that master The main node is lovelorn At this time, it is objectively considered that the master node is disconnected

#sentinel  monitor <master-name> <ip> <redis-port> <quorum>

sentinel  monitor  mymaster 127.0.0.1 6379 2

# When in Redis In the example, the requirepass foobared Authorization code So all connections Redis The client of the instance must provide the password

# Set up a sentry sentinel Password to connect master and slave Note that the same verification code must be set for master and slave

#sentinel auth-pass <master-name> <password>

sentinel  auth-pass mymaster  MySUPER--secret-0123password

# Specify how many milliseconds later   The master node didn't answer the sentry sentinel  here Sentinels subjectively think that the primary node is offline Default 30 second

#sentinel down-after-milliseconds <master-name> <milliseconds>

sentinel  down-after-milliseconds  mymaster 30000

# This configuration item specifies when sending failover How many can there be at most during the primary / standby handover slave Simultaneously on the new master Conduct Sync

The smaller the number , complete failover The longer it takes

But if the number is bigger , It means the more slave because replication And is not available

You can do this by setting this value to zero 1 To make sure there's only one at a time slave In a state where command requests cannot be processed .

#sentinel parallel-syncs <master-name> <numslaves>

sentinel parallel-syncs  mymaster 1

# Timeout for failover failover-timeout It can be used in the following aspects ：

#1、 The same sentinel To the same master two failover The time between

#2、 When one slave From a wrong one master Where the synchronized data starts to calculate the time . until slave Corrected to be correct master Where the data is synchronized

#3、 When you want to cancel an ongoing failover The time required

#4、 When doing failover when , Configure all slaves Point to the new master Maximum time required , however , Even after this timeout ,slaves It will still be correctly configured to point to master, But it won't parallel-syncs Here comes the configured rule

# Default three minutes

#sentinel failover-timeout  <master-name> <milliseconds>

sentinel failover-timeout mymaster 180000

#SCRIPTS  EXECUTION

# Configure the script to be executed when sending at a certain time , The administrator can be notified by script , For example, when the system is not running normally, send an email to inform the relevant personnel

# There are the following rules for the result of the script ：

# If the script returns 1, Then the script will be executed again later , The number of repetitions currently defaults to 10

# If the script returns 2, Or 2 A higher return value , The script will not repeat

# If the script is terminated during execution due to receiving a system interrupt , Then the same return value is 1 The same behavior when .

# The maximum execution time of a script is 60s, If I exceed that time , The script will be a SIGKILL Signal termination , And then re execute

# Notification scripts ： When sentinel When any warning level event occurs （ for instance reids Subjective failure and objective failure of examples, etc ）, This script will be called , At this point the script should be sent by email ,SMS Wait for the way to inform the system administrator about the abnormal operation of the system . When the script is called , Two parameters will be passed to the script , One is the type of event , One is the description of the event . If sentinel.conf The script path is configured in the configuration file , Then you have to make sure that the script exists in this path , And it's executable , otherwise sentinel Failed to start normally successfully .

# Notification script

#sentinel  notification-script  <master-name> <script-path>

sentinel notification-script mymaster  /var/redis/notify.sh

# The client reconfigures the master node parameter script

# When one master because failover And when it changes , This script will be called , Notify related clients about master Information that the address has changed .

# The following parameters will be passed to the script when the script is called ：

#<master-name> <role> <state> <from-ip> <from-port> <to-ip> <tp-port>

# at present <state> Always “failover”

#<role> yes “leader” perhaps “observer” One of them .

# Parameters from-ip,from-port, to-ip,to-port It's for the old master And the new master（ I.e. old slave） communication

# This script should be generic , Can be called many times , It's not targeted .

#sentinel  client-reconfig-script <master-name> <script-path>

sentinel  client-reconfig-scirpt  mymaster /var/redis/reconfig.sh