实现redis哨兵，模拟master故障场景
由于主从架构无法实现master和slave角色的自动切换，所以在发送master节点宕机时，redis主从复制无法实现自动的故障转移，即将slave 自动提升为新的master。因此，需要配置哨兵来"盯"着它们干活，一旦发现master节点宕机，会快速的将slave节点提升为新master节点。
一、实现主从复制架构
1.1 安装redis
#在所有节点都安装redis
yum install redis -y
1.2 修改配置文件
#所有节点都修改如下：
[root@localhost ~]#vim /etc/redis.conf
# replicaof <masterip> <masterport>
replicaof 10.0.0.8 6379 #指定master的IP和端口号
....省略
# masterauth <master-password>
masterauth 123456
...省略
1.3 启动redis
# systemctl enable --now redis
# ss -ntl
ss -State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 511 0.0.0.0:6379 0.0.0.0:*
...省略...
1.4 查看主从复制状态
#在master节点查看到如下内容:
[root@localhost ~]#redis-cli -a 123456 info replication
Warning: Using a password with '-a' or '-u' option on the command line interface may not be safe.
# Replication
role:master
connected_slaves:2
slave0:ip=10.0.0.18,port=6379,state=online,offset=6398,lag=0
slave1:ip=10.0.0.28,port=6379,state=online,offset=6398,lag=1
master_failover_state:no-failover
master_replid:1d5939408b470ad048e8e397b2c258836c6caa73
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:6398
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:6398
二、配置哨兵
2.1 实现哨兵
Sentinel实际上是一个特殊的redis服务器,有些redis指令支持,但很多指令并不支持.默认监听在26379/tcp端口。
##每个节点配置相同
# cp /etc/redis-sentinel.conf{,.bak}
# cat > /etc/redis-sentinel.conf<<EOF
bind 0.0.0.0
port 26379
daemonize yes
pidfile "/var/run/redis-sentinel.pid"
logfile "/var/log/sentinel_26379.log"
dir "/tmp"
sentinel monitor mymaster 10.0.0.8 6379 2
sentinel auth-pass mymaster 123456
sentinel down-after-milliseconds mymaster 30000
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 180000
sentinel deny-scripts-reconfig yes
EOF
# mdkri /var/log/redis #创建log目录
# systemctl enable --now redis-sentinel.service
# ss -ntl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 511 0.0.0.0:26379 0.0.0.0:*
LISTEN 0 511 0.0.0.0:6379 0.0.0.0:*
LISTEN 0 128 0.0.0.0:111 0.0.0.0:*
LISTEN 0 128 0.0.0.0:22 0.0.0.0:*
LISTEN 0 100 127.0.0.1:25 0.0.0.0:*
LISTEN 0 511 [::1]:6379 [::]:*
LISTEN 0 128 [::]:111 [::]:*
LISTEN 0 128 [::]:22 [::]:*
LISTEN 0 100 [::1]:25 [::]:*
2.2检查哨兵状态
[root@localhost ~]#redis-cli -p 26379 info sentinel
# Sentinel
sentinel_masters:1
sentinel_tilt:0
sentinel_running_scripts:0
sentinel_scripts_queue_length:0
sentinel_simulate_failure_flags:0
master0:name=mymaster,status=ok,address=10.0.0.8:6379,slaves=2,sentinels=1
#查看日志，观察启动过程
[root@localhost ~]#tail -f /var/log/redis/sentinel.log
6206:X 07 Feb 2022 23:30:54.262 # Configuration loaded
6206:X 07 Feb 2022 23:30:54.263 * Increased maximum number of open files to 10032 (it was originally set to 1024).
6206:X 07 Feb 2022 23:30:54.263 * monotonic clock: POSIX clock_gettime
6206:X 07 Feb 2022 23:30:54.264 * Running mode=sentinel, port=26379.
6206:X 07 Feb 2022 23:30:54.266 # Sentinel ID is 9fa9b4b370f49ca201d9d52bb28bb7d41c95ff65
6206:X 07 Feb 2022 23:30:54.266 # +monitor master mymaster 10.0.0.8 6379 quorum 2
6206:X 07 Feb 2022 23:30:54.267 * +slave slave 10.0.0.18:6379 10.0.0.18 6379 @ mymaster 10.0.0.8 6379
6206:X 07 Feb 2022 23:30:54.268 * +slave slave 10.0.0.28:6379 10.0.0.28 6379 @ mymaster 10.0.0.8 6379
6206:X 07 Feb 2022 23:30:55.548 * +sentinel sentinel ca0733135183c8aebf666f068e9134e3adffc362 10.0.0.8 26379 @ mymaster 10.0.0.8 6379
6206:X 07 Feb 2022 23:31:10.040 * +sentinel sentinel 48b97abdf2a0628bb425291e968c25a7ecc6e19d 10.0.0.28 26379 @ mymaster 10.0.0.8 6379
三、模拟master故障场景
3.1 模拟故障，停掉master
停掉身为master的主机10.0.0.8
# systemctl stop redis
3.2 查看日志
3.3 故障恢复
# systemctl start redis
3.4 观察变化
可以发现，当master恢复重新加入回来后，并没有重新获得master，而是以slave身份存在。
