Shulou(Shulou.com)06/01 Report--

Sentinel (Sentinel) is a tool for monitoring the status of Master in redis clusters and is a high availability solution for Redis. Sentinel Sentinel mode has been integrated into post-redis2.4 versions. Sentinel is a highly available solution for redis. The sentinel system can monitor one or more redis master services and all slave services of these master services; when a master service goes offline, automatically upgrade a slave service under the master to a master service to replace the offline master service to continue to process requests.

Sentinel allows redis to achieve master-slave replication. When the master in a cluster fails, sentinel can elect a new master to automatically take over the work of master, and other redis servers in the cluster automatically point to the new master synchronization data. It is generally recommended that an odd number of sentinel should be used to prevent a sentinel from being unable to connect to the master and lead to misswitching.

Redis-Sentinel is a high availability (HA) solution officially recommended by Redis. When Redis is used as a high-availability solution for Master-slave, if master goes down, Redis itself (including many of its clients) does not automatically switch between master and slave, and Redis-sentinel itself is also an independent process, which can monitor multiple master-slave clusters and switch automatically when master is down. Sentinel Sentinel system, which consists of one or more Sentinel instances, 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.

How Sentinel works (scheduled tasks performed by each Sentinel instance)

1) each Sentinel sends a PING command to its known Master,Slave and other Sentinel instances at a frequency of once per second.

2) if the time between instance and the last valid reply to a PING command exceeds the value specified in the own-after-milliseconds option, the instance will be marked as subjectively offline by Sentinel.

3) if a Master is marked as subjectively offline, all Sentinel that are monitoring the Master should confirm that the Master has indeed entered the subjective offline state at a frequency of once per second.

4) when a sufficient number of Sentinel (greater than or equal to the value specified in the configuration file) confirms that Master has indeed entered the subjective offline state within the specified time range, Master will be marked as objective offline.

5) in general, each Sentinel sends INFO commands to all Master,Slave it knows at a frequency of once every 10 seconds.

6) when Master is marked as objective offline by Sentinel, the frequency of Sentinel sending INFO commands to all Slave of offline Master will be changed from once in 10 seconds to once per second.

7) if there is not enough Sentinel to agree that Master has been taken offline, the objective offline status of Master will be removed. If Master returns a valid reply to Sentinel's PING command, the subjective offline state of Master will be removed.

Environment:

Host IP:

192.168.121.121

192.168.121.122

192.168.121.123

System: centos7.6

Upload source code packet to host

Redis-4.0.11.tar.gz

1. Compilation by three hosts

Yum install gcc gcc-c++-y

Tar-zxf redis-4.0.11.tar.gz-C / data/usr/src

Cd / data/usr/src/redis-4.0.11/

Make & & make install PREFIX=/data/usr/redis

2. Three hosts can copy configuration files

Mkdir / data/usr/redis/ {conf,data,logs}

Cp * .conf / data/usr/redis/conf

Edit configuration file

Cd / data/usr/redis/conf

2.1.Configuring redis

Primary node:

Vi redis.conf

Bind 127.0.0.1 192.168.121.121

Protected-mode no

Daemonize yes

Slave-priority 100

Appendonly yes

Dir / data/usr/redis/data

Requirepass "Redis2019!"

Masterauth "Redis2019!"

Logfile "/ data/usr/redis/logs/redis.log"

Two slave nodes:

Bind 127.0.0.1 192.168.121.122

Protected-mode no

Daemonize yes

Slave-priority 90

Appendonly yes

Dir / data/usr/redis/data

Slaveof 192.168.121.121 6379

Requirepass "Redis2019!"

Masterauth "Redis2019!"

Logfile "/ data/usr/redis/logs/redis.log"

Bind 127.0.0.1 192.168.121.123

Protected-mode no

Daemonize yes

Slave-priority 90

Appendonly yes

Dir / data/usr/redis/data

Slaveof 192.168.121.121 6379

Requirepass "Redis2019!"

Masterauth "Redis2019!"

Logfile "/ data/usr/redis/logs/redis.log"

2.2. Configure sentinels

Vi sentinel.conf

Protected-mode no

Daemonize yes

Logfile "/ data/usr/redis/logs/sentinel.log"

Sentinel monitor mymaster 192.168.121.121 6379 2 # sets the main name, ip address, port number, and the number of sentinels participating in the election.

Sentinel auth-pass mymaster Redis2019!

The last two items should be configured in order.

3. Start

Start the redis service: start master first and then slave

/ data/usr/redis/bin/redis-server / data/usr/redis/conf/redis.conf

View redis service status

/ data/usr/redis/bin/redis-cli-h 192.168.121.121-p 6379-a Redis2019! Info replication

/ data/usr/redis/bin/redis-cli-h 192.168.121.122-p 6379-a Redis2019! Info replication

/ data/usr/redis/bin/redis-cli-h 192.168.121.123-p 6379-a Redis2019! Info replication

Start the sentinel service: start the redis service first and then start the sentinel service, and turn off the reverse, first shut down the sentinel service, and then shut down the redis service.

/ data/usr/redis/bin/redis-sentinel / data/usr/redis/conf/sentinel.conf

Check the Sentinel service status

/ data/usr/redis/bin/redis-cli-h 192.168.121.121-p 26379 info sentinel

/ data/usr/redis/bin/redis-cli-h 192.168.121.122-p 26379 info sentinel

/ data/usr/redis/bin/redis-cli-h 192.168.121.123-p 26379 info sentinel

4. Test

4.1. Synchronous testing

Primary node:

192.168.121.121 6379 > set name kkk

Slave node:

192.168.121.122 6379 > keys *

1) "name"

192.168.121.122 6379 > get name

"kkk"

192.168.121.123 6379 > keys *

1) "name"

192.168.121.123purl 6379 > get name

"kkk"

4.2. Read-only test from the library

192.168.121.122 6379 > set bname yyy

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

192.168.121.123purl 6379 > set bname yyy

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

4.3, redundancy testing

The test stops the master redis and finds that one of the slave changes to the master. After starting the stopped service, it is found that it is a slave service, and the master service remains unchanged.

Stop a node sentinel service, then stop the master service, and find that one of the slave services is upgraded to the master service.

Stop Sentinel Service order

/ data/usr/redis/bin/redis-cli-h 192.168.121.121-p 26379 shutdown

Stop redis service command

/ data/usr/redis/bin/redis-cli-h 192.168.121.122-p 6379-a Redis2019 shutdown

Stop the second sentinel service, and then stop the redis primary service. It is found that there is no primary service in the remaining redis service, indicating that there must be at least two sentinel services, preferably three or more.

5. Problem handling

5.1. execute make PREFIX=/data/usr/redis install to report an error

Cc: error:.. / deps/hiredis/libhiredis.a: No such file or directory

Cc: error:.. / deps/lua/src/liblua.a: No such file or directory

Cd deps/

Ls

Hiredis jemalloc linenoise lua Makefile README.md update-jemalloc.sh

Cd hiredis

Make

Cd linenoise

Make

Cd lua

Make

Cd lua

Make

Compiler error report

Please do

Make PLATFORM

Where PLATFORM is one of these:

Aix ansi bsd freebsd generic linux macosx mingw posix solaris

See INSTALL for complete instructions.

[root@slave1 lua] # make PLATFORM

Make: * No rule to make target `PLATFORM'. Stop.

Execute the following command to compile

Make generic

5.2. Error starting Sentinel

. / redis-sentinel sentinel.conf

* FATAL CONFIG FILE ERROR * *

Reading the configuration file, at line 92

> 'sentinel auth-pass mymaster Redis2019'

No such master with specified name.

An error occurred:

Sentinel monitor mymaster 192.168.121.123 6379 2

Sentinel auth-pass mymaster Redis2019

The configuration above should be in order, and the error is caused by the configuration of the above item below.

Reference:

Https://www.cnblogs.com/kevingrace/p/9004460.html

Https://blog.csdn.net/qq_40476230/article/details/85845166

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