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This article mainly explains "how to build Sentinel Cluster in redis". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "how to build Sentinel clusters in redis".

Redis installation and deployment

Environment description:

Redis uses version 6.2.6

Host IP system master192.168.129.136redhat8slave192.168.182.135redhat8slave2192.168.182.134redhat8

Preparatory work

/ / all three hosts need to do [root@master opt] wget https://download.redis.io/releases/redis-6.2.6.tar.gz// all do [root@master opt] # tar-zxf redis-6.2.6.tar.gz / / compile and install [root@master redis-6.2.6] # pwd / / enter the redis directory / opt/redis-6.2.6 [root@master redis-6.2.6] # Yum-y install gcc gcc-c++ / / install C language compiler [root@master redis-6.2.6] # yum-y install make / / install make compiler [root@master redis-6.2.6] # make MALLOC=libc

Configure environment variables

/ / the binaries of redis are placed in the src directory [root@master redis-6.2.6] # cat / etc/profile.d/redis.sh / / in order to directly use the redis command export PATH=/opt/redis-6.2.6/src:$PATH [root@master redis-6.2.6] # source / etc/profile.d/redis.sh / / to make it effective / / there are two ways to start redis: [root@master redis- 6.2.6] # vim redis.conf257 daemonize yes / / change no to yes startup one: [root@master src] # / redis-server / / it is not recommended to start [root@master redis-6.2.6] # redis-server / opt/redis-6.2.6/redis.conf / / it is recommended to use this way to start two: [root@master opt] # cat / usr/lib/systemd/system/redis.service [Unit] Description=redis server DaemonAfter= network.target [service] Type=forkingExecStart=/opt/redis-6.2.6/src/redis-server / opt/redis-6.2.6/redis.confExecStop=/bin/kill-s QUIT $MAINPIDExecReload=/bin/kill-HUP $MAINPID [install] WantedBy=multi-user.target [root@master opt] # systemctl daemon-reload [root@master opt] # systemctl enable-- now redis.service [root@master opt] # ss-anlt | awk-F "* |:" NR==2 {print $5}'/ / see 6379 port number indicates that the command redis-cli-p 6379 127.0.0.1 redis-cli 6379 > [root@master redis-6.2.6] # redis-cli-p 6379 shutdown / / shuts down the redis service

All the above operations need to be done by the three hosts.

Redis cluster architecture

The Sentinel cluster deployed now is based on redis master and slave, and the overall structure is as follows:

A master node (master) can have multiple slave nodes (slave), and the slave node can replicate the master node to ensure data synchronization. Sentinel monitors each node, including master node survival detection, master-slave operation detection and so on. Once the master node is down, Sentinel can automatically fail over (failover) and master-slave switching.

Configure redis Master and Slave

Modify redis configuration file

It is recommended that you write a backup before modifying the configuration file

/ / what to do in master [root@master redis-6.2.6] # mkdir logs75 bind 192.168.129.136 / / Native IP address 94 protected-mode no 302 logfile "/ opt/redis-6.2.6/logs/redis.log"

Note that replicaof specifies the IP address and port number of master, what to do on the old version slaveof

/ / what to do on slave2 [root@slave2 redis-6.2.6] # vim redis.conf75 bind 192.168.129.135 / / Native IP477 replicaof 192.168.129.136 6379 master IP and port number / / what to do on slave2 [root@slave2 redis-6.2.6] # vim redis.conf75 bind 192.168.129.135 / / Native IP477 replicaof 192.168.129.136 6379 master IP and port number

Note that after modifying the configuration file, you need to restart the redis service to take effect.

Test master / slave [root@master redis-6.2.6] # redis-cli-h 192.168.129.136-p 6379192.168.129.136 purl 6379 > set name tom / / set a value OK [root@slave ~] # redis-cli-h 192.168.129.135 / / you can also not specify a port number here Because redis defaults to the use of port number 192.168.129.135redis-cli 6379 > get name "tom" [root@slave2 redis-6.2.6] # redis-cli-h 192.168.129.134192.168.129.134tom 6379 > get name "tom" # Master-Slave Sentinel Cluster description:

Redis Sentinel is Redis's high availability solution consisting of one or more Sentinel (Sentinel) instances. It can monitor any number of master servers and all slave servers under these master servers, and automatically upgrade a slave server under the offline master server to a new master server when the monitored master server goes offline. Its main functions are as follows:

Monitoring: Sentinel will constantly check whether your master server and slave server are working properly.

Notification: when there is a problem with a monitored Redis server, Sentinel can send a notification to the administrator or other application through API.

Failover: when the master server does not work properly, Sentinel will automatically fail over, that is, master-slave switchover.

Unified configuration management: the connector asks sentinel to get the address of the master and slave.

Sentinel cluster principle

The core of the algorithm used by Sentinel is Raft algorithm, which is mainly used for distributed systems, system fault tolerance, and Leader election. Each Sentinel needs to perform the following tasks on a regular basis:

Each Sentinel automatically discovers other Sentinel and slave servers, sending a PING command once per second to the master server, slave server, and other Sentinel instances it knows.

If an instance (instance) takes longer than the value specified in the down-after-milliseconds option from the last valid reply to the PING command, the instance will be marked as subjectively offline by Sentinel. Valid responses can be: + PONG,-LOADING, or-MASTERDOWN.

If a primary server is marked as subjectively offline, then all Sentinel that is monitoring the primary server should confirm that the primary server has indeed entered the subjective offline state at a frequency of once per second.

If a primary server is marked as subjectively offline and a sufficient number of Sentinel (at least up to the number specified in the profile) agrees with this judgment within a specified time frame, then the primary server is marked as objective offline.

In general, each Sentinel sends INFO commands to all master and slave servers it knows at a frequency of once every 10 seconds. When a master server is marked as objective offline by Sentinel, the frequency of Sentinel sending INFO commands to all slave servers of the offline master server will be changed from once in 10 seconds to once per second.

When there is not enough Sentinel to agree that the primary server has gone offline, the objective offline status of the primary server will be removed. When the primary server returns a valid reply to the Sentinel PING command, the supervisor offline status of the primary server is removed.

Sentinel cluster / / three hosts do the same operation [root@master redis-6.2.6] # vim sentinel.conf26 daemonize yes36 logfile "/ opt/redis-6.2.6/logs/sentinel.conf" 84 sentinel monitor mymaster 192.168.129.136 6379 2 [root@master ~] # redis-sentinel / opt/redis-6.2.6/sentinel.conf / / start Sentinel / / View Sentinel information [root@master ~] # redis-cli-h 192 .168.129.136-p 26379192.168.129.136 purl 26379 > info sentinel# Sentinelsentinel_masters:1sentinel_tilt:0sentinel_running_scripts:0sentinel_scripts_queue_length:0sentinel_simulate_failure_flags:0master0:name=mymaster Status=ok,address=192.168.129.136:6379,slaves=2,sentinels=3 [root@slave ~] # redis-cli-h 192.168.129.135-p 26379192.168.129.135 redis-cli 26379 > info sentinel# Sentinelsentinel_masters:1sentinel_tilt:0sentinel_running_scripts:0sentinel_scripts_queue_length:0sentinel_simulate_failure_flags:0master0:name=mymaster,status=ok,address=192.168.129.136:6379,slaves=2 Sentinels=3 [root@slave2 ~] # redis-cli-h 192.168.129.134-p 26379192.168.129.134 redis-cli 26379 > info sentinel# Sentinelsentinel_masters:1sentinel_tilt:0sentinel_running_scripts:0sentinel_scripts_queue_length:0sentinel_simulate_failure_flags:0master0:name=mymaster,status=ok,address=192.168.129.136:6379,slaves=2,sentinels=3

Simulate host failure and carry out disaster recovery switching

[root@master ~] # systemctl stop redis.service / / close the redis service [root@master redis-6.2.6] # ps-ef | grep redis / / use this command to find the sentinel process, and then kill the sentinel process / / because the host has switched to 144host, so the configuration file of the original host will be changed accordingly, so the configuration file needs to be changed before 137startup Configure it as a 144th slave: [root@master redis-6.2.6] # vim redis.conf477 replicaof 192.168.129.134 6379 [root@master redis-6.2.6] # redis-server / opt/redis-6.2.6/redis.conf / / start the redis service [root@master redis-6.2.6] # systemctl restart redis.service / / you can also use this command to start the redis service [root@master redis-6.2.6] # redis-sentinel / opt/redis-6.2.6/sentinel.conf / / start the sentinel service # # so far the Sentinel cluster has been built I believe you have a deeper understanding of "how to build Sentinel clusters in redis". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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