发布时间：2023-08-06 18:00
当主服务器宕机之后，需要手动把一台从服务器切换为主服务器。它可以检测服务主机是否出现故障，如果故障了就根据投票数自动将从机转换主机。
假如某个Redis服务出现了故障，哨兵A检测不到它了，他不会立刻选举新的主机，其他哨兵也发现它不可以用了这时候才会发起投票，选取新的主机。（投票会有个投票算法）。
首先创建文件sentinel.conf编辑文件
#禁止保护模式
#protected-mode no
#配置监听主服务器
#sentinel monitor 代表监控
#mymaster 服务器名字 可以自定义随便起
#服务器远程ip 一定要写远程ip 否则远程调用会爆无法找到的错误
#端口 主机服务器的端口
#1 当一个哨兵或者一个以上认为这个服务器不可以了 进行切换主机操作
sentinel monitor mymaster 服务器远程ip 端口 1
#sentinel auth-pass 定义主机密码
#mymaster 代表服务器名字
#您的密码 服务器密码
sentinel auth-pass mymaster 您的密码
# 3s内mymaster服务器无响应，则认为mymaster死了
sentinel down-after-milliseconds mymaster 3000
#指定在故障切换准许的毫秒数，当超过这个毫秒数的时候，就认为切换故障失败，默认三分钟
sentinel failover-timeout mymaster 10000
#端口
port 26379
启动哨兵
输入redis-sentinel sentinel.conf
[root@VM-0-3-centos redis-6.0.7]# redis-sentinel sentinel.conf
6381:X 24 Oct 2020 18:27:30.285 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
6381:X 24 Oct 2020 18:27:30.285 # Redis version=6.0.7, bits=64, commit=00000000, modified=0, pid=6381, just started
6381:X 24 Oct 2020 18:27:30.285 # Configuration loaded
6381:X 24 Oct 2020 18:27:30.286 # Could not create server TCP listening socket *:26379: bind: Address already in use
[root@VM-0-3-centos redis-6.0.7]# kill 5360
[root@VM-0-3-centos redis-6.0.7]# redis-sentinel sentinel.conf
6420:X 24 Oct 2020 18:27:45.915 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
6420:X 24 Oct 2020 18:27:45.915 # Redis version=6.0.7, bits=64, commit=00000000, modified=0, pid=6420, just started
6420:X 24 Oct 2020 18:27:45.915 # Configuration loaded
_._
_.-``__ ''-._
_.-`` `. `_. ''-._ Redis 6.0.7 (00000000/0) 64 bit
.-`` .-```. ```\/ _.,_ ''-._
( ' , .-` | `, ) Running in sentinel mode
|`-._`-...-` __...-.``-._|'` _.-'| Port: 26379
| `-._ `._ / _.-' | PID: 6420
`-._ `-._ `-./ _.-' _.-'
|`-._`-._ `-.__.-' _.-'_.-'|
| `-._`-._ _.-'_.-' | http://redis.io
`-._ `-._`-.__.-'_.-' _.-'
|`-._`-._ `-.__.-' _.-'_.-'|
| `-._`-._ _.-'_.-' |
`-._ `-._`-.__.-'_.-' _.-'
`-._ `-.__.-' _.-'
`-._ _.-'
`-.__.-'
6420:X 24 Oct 2020 18:27:45.917 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
6420:X 24 Oct 2020 18:27:45.917 # Sentinel ID is 11fe5799a638325f787d12014d650fb3b034b7ef
6420:X 24 Oct 2020 18:27:45.917 # +monitor master mymaster 175.24.118.135 6379 quorum 1 # 主机
6420:X 24 Oct 2020 18:27:55.926 * +fix-slave-config slave 127.0.0.1:6380 127.0.0.1 6380 @ mymaster 175.24.118.135 6379 # 他的从机
让主服务器故意宕机
[root@VM-0-3-centos redis-6.0.7]# redis-cli -p 6379
127.0.0.1:6379> AUTH 您的密码
OK
127.0.0.1:6379> set a 12
OK
127.0.0.1:6379> keys *
1) "a"
127.0.0.1:6379> SHUTDOWN
not connected> exit
过一会哨兵会进行投票模式选举新的服务器
30489:X 12 Sep 2020 14:12:25.853 # +sdown master sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:25.853 # +odown master sentry1 127.0.0.1 6379 #quorum 1/1
30489:X 12 Sep 2020 14:12:25.853 # +new-epoch 1
30489:X 12 Sep 2020 14:12:25.853 # +try-failover master sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:25.860 # +vote-for-leader 79910bee84ce8bbc7916f3d1aafae1a4c769f48c 1
30489:X 12 Sep 2020 14:12:25.860 # +elected-leader master sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:25.860 # +failover-state-select-slave master sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:25.927 # +selected-slave slave 127.0.0.1:6381 127.0.0.1 6381 @ sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:25.927 * +failover-state-send-slaveof-noone slave 127.0.0.1:6381 127.0.0.1 6381 @ sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:25.998 * +failover-state-wait-promotion slave 127.0.0.1:6381 127.0.0.1 6381 @ sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:26.934 # +promoted-slave slave 127.0.0.1:6381 127.0.0.1 6381 @ sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:26.934 # +failover-state-reconf-slaves master sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:27.014 * +slave-reconf-sent slave 127.0.0.1:6380 127.0.0.1 6380 @ sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:28.020 * +slave-reconf-inprog slave 127.0.0.1:6380 127.0.0.1 6380 @ sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:28.020 * +slave-reconf-done slave 127.0.0.1:6380 127.0.0.1 6380 @ sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:28.073 # +failover-end master sentry1 127.0.0.1 6379
30489:X 12 Sep 2020 14:12:28.073 # +switch-master sentry1 127.0.0.1 6379 127.0.0.1 6381
30489:X 12 Sep 2020 14:12:28.073 * +slave slave 127.0.0.1:6380 127.0.0.1 6380 @ sentry1 127.0.0.1 6381
30489:X 12 Sep 2020 14:12:28.073 * +slave slave 127.0.0.1:6379 127.0.0.1 6379 @ sentry1 127.0.0.1 6381
查看选举为主机的服务器
[root@VM-0-3-centos redis-6.0.7]# redis-cli -p 6381
127.0.0.1:6381> AUTH 您的密码
OK
127.0.0.1:6381> info replication
# Replication
role:master
connected_slaves:1
slave0:ip=127.0.0.1,port=6380,state=online,offset=111034,lag=1
master_replid:ff82da3fdcd20b89d43725f5367a583db93b8275
master_replid2:f450fba3dd58a2374f5abee13b6b09024823328e
master_repl_offset:111048
second_repl_offset:103876
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:183
repl_backlog_histlen:110866
如果主机宕机之后又回来了
如果主机回来了 只能当新的主机的仆人
127.0.0.1:6379> info replication
# Replication
role:slave
master_host:127.0.0.1
master_port:6381
master_link_status:down
master_last_io_seconds_ago:-1
master_sync_in_progress:0
slave_repl_offset:1
master_link_down_since_seconds:1599891656
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:51d2c7f4ba58e375c88285ab6d437d7a23fab39c
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0
优点:
1.哨兵集群，基于主从复制，主从复制所有优点他手有
2.主从是可以切换的，故障可以转移。系统可用性会更好
缺点：
1.Redis不好在线扩容，集群容量一旦达到上限，在线扩展十分麻烦。
2.哨兵模式配置很麻烦
application.yml
spring:
redis:
password: 哨兵密码# 哨兵密码
sentinel:
nodes: 服务器ip:端口 # 哨兵ip:端口
master: 服务器名字# 哨兵名字
接下来使用就跟正常一样了。