1 redis 集群介绍
主从架构无法实现master和slave角色的自动切换，即当master出现redis服务异常、主机断电、磁盘损坏等问题导致master无法使用，而redis主从复制无法实现自动的故障转移(将slave 自动提升为新master)，需要手动修改环境配置,才能切换到slave redis服务器，另外当单台Redis服务器性能无法满足业务写入需求的时候,也无法横向扩展Redis服务的并行写入性能
需要解决以上的两个核心问题：
- master和slave角色的无缝切换，让业务无感知从而不影响业务使用
- 可横向动态扩展Redis服务器，从而实现多台服务器并行写入以实现更高并发的目的。
2.原理
Sentinel 进程是用于监控redis集群中Master主服务器工作的状态，在Master主服务器发生故障的时候，可以实现Master和Slave服务器的切换，保证系统的高可用，哨兵(Sentinel) 是一个分布式系统，可以在一个架构中运行多个哨兵(sentinel) 进程，这些进程使用流言协议(gossip protocols)来接收关于Master主服务器是否下线的信息，并使用投票协议(Agreement Protocols)来决定是否执行自动故障迁移,以及选择哪个Slave作为新的Master
Redis Sentinel中的Sentinel节点个数应该为大于等于3且最好为奇数客户端初始化时连接的是Sentinel节点集合，不再是具体的Redis节点，但Sentinel只是配置中心不是代理。
2.1 sentinel中的三个定时任务
- 每10秒每个sentinel对master和slave执行info
发现slave节点
确认主从关系 - 每2秒每个sentinel通过master节点的channel交换信息(pub/sub)
通过sentinel__:hello频道交互
交互对节点的“看法”和自身信息 - 每1秒每个sentinel对其他sentinel和redis执行ping
3 实现哨兵
3.1 哨兵的准备实现主从复制架构
哨兵的前提是已经实现了一个redis的主从复制的运行环境，从而实现一个一主两从基于哨兵的高可用redis架构
#在所有主从节点执行
[root@centos8 ~]#dnf -y install redis
[root@centos8 ~]#vim /etc/redis.conf
bind 0.0.0.0
masterauth "123456" #实例作为从节点时，使用此配置项来设置连接主节点所需的密码
requirepass "123456"
#在所有从节点执行
[root@centos8 ~]#echo "replicaof 10.0.0.8 6379" >> /etc/redis.conf
#在所有主从节点执行
[root@centos8 ~]#systemctl enable --now redis
master服务器状态
~~~shell
[root@redis-master ~]#redis-cli -a 123456
Warning: Using a password with '-a' or '-u' option on the command line interface
may not
127.0.0.1:6379> INFO replication
# Replication
role:master
connected_slaves:2
slave0:ip=10.0.0.28,port=6379,state=online,offset=112,lag=1
slave1:ip=10.0.0.18,port=6379,state=online,offset=112,lag=0
master_replid:8fdca730a2ae48fb9c8b7e739dcd2efcc76794f3
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:112
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:112
127.0.0.1:6379>
配置slave1
[root@redis-slave1 ~]#redis-cli -a 123456
Warning: Using a password with '-a' or '-u' option on the command line interface
may not be safe.
127.0.0.1:6379> REPLICAOF 10.0.0.8 6379
OK
127.0.0.1:6379> CONFIG SET masterauth "123456"
OK
127.0.0.1:6379> INFO replication
# Replication
role:slave
master_host:10.0.0.8
master_port:6379
master_link_status:up
master_last_io_seconds_ago:4
master_sync_in_progress:0
slave_repl_offset:140
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:8fdca730a2ae48fb9c8b7e739dcd2efcc76794f3
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:140
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:99
repl_backlog_histlen:42
配置slave2
[root@redis-slave2 ~]#redis-cli -a 123456
Warning: Using a password with '-a' or '-u' option on the command line interface
may not be safe.
127.0.0.1:6379> REPLICAOF 10.0.0.8 6379 #从节点会尝试连接主节点并开始复制数据
OK
127.0.0.1:6379> CONFIG SET masterauth "123456" #设置了从节点连接主节点所需的密码
OK
127.0.0.1:6379> INFO replication
# Replication
role:slave
master_host:10.0.0.8
master_port:6379
master_link_status:up
master_last_io_seconds_ago:3
master_sync_in_progress:0
slave_repl_offset:182
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:8fdca730a2ae48fb9c8b7e739dcd2efcc76794f3
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:182
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:15
repl_backlog_histlen:168
127.0.0.1:6379>
3.2 编辑哨兵的配置文件
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,哨兵可以不和Redis服务器部署在一起，但一般部署在一起以节约成本
[root@centos8 ~]#vim /etc/redis-sentinel.conf
[root@redis-master ~]#grep -vE "^#|^$" /etc/redis-sentinel.conf
port 26379
daemonize no
pidfile "/var/run/redis-sentinel.pid"
logfile "/var/log/redis/sentinel.log"
dir "/tmp"
sentinel monitor mymaster 10.0.0.8 6379 2 #修改此行
sentinel auth-pass mymaster 123456 #增加此行
sentinel down-after-milliseconds mymaster 3000 #修改此行
sentinel parallel-syncs mymaster 1
sentinel failover-timeout mymaster 180000
sentinel deny-scripts-reconfig yes
#注意此行自动生成必须唯一,一般不需要修改，如果相同则修改此值需重启redis和sentinel服务
sentinel myid 50547f34ed71fd48c197924969937e738a39975b
.....
# Generated by CONFIG REWRITE
protected-mode no
supervised systemd
sentinel leader-epoch mymaster 0
sentinel known-replica mymaster 10.0.0.28 6379
sentinel known-replica mymaster 10.0.0.18 6379
sentinel current-epoch 0
[root@redis-master ~]#scp /etc/redis-sentinel.conf redis-slave1:/etc/
[root@redis-master ~]#scp /etc/redis-sentinel.conf redis-slave2:/etc/
3.3 启动哨兵
三台哨兵服务器都要启动
#确保每个哨兵主机myid不同，如果相同，必须手动修改为不同的值
[root@redis-slave1 ~]#vim /etc/redis-sentinel.conf
sentinel myid 50547f34ed71fd48c197924969937e738a39975c
[root@redis-slave2 ~]#vim /etc/redis-sentinel.conf
sentinel myid 50547f34ed71fd48c197924969937e738a39975d
[root@redis-master ~]#systemctl enable --now redis-sentinel.service
[root@redis-slave1 ~]#systemctl enable --now redis-sentinel.service
[root@redis-slave2 ~]#systemctl enable --now redis-sentinel.service
3.4 验证哨兵端口
[root@redis-master ~]#ss -ntl
State Recv-Q Send-Q Local Address:Port Peer Address:Port
LISTEN 0 128 0.0.0.0:22 0.0.0.0:*
LISTEN 0 128 0.0.0.0:26379 0.0.0.0:*
LISTEN 0 128 0.0.0.0:6379 0.0.0.0:*
LISTEN 0 128 [::]:22 [::]:*
LISTEN 0 128 [::]:26379 [::]:*
LISTEN 0 128 [::]:6379 [::]:*
3.5 查看哨兵日志
master的哨兵日志
[root@redis-master ~]#tail -f /var/log/redis/sentinel.log
38028:X 20 Feb 2020 17:13:08.702 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
38028:X 20 Feb 2020 17:13:08.702 # Redis version=5.0.3, bits=64,
commit=00000000, modified=0, pid=38028, just started
38028:X 20 Feb 2020 17:13:08.702 # Configuration loaded
38028:X 20 Feb 2020 17:13:08.702 * supervised by systemd, will signal readiness
38028:X 20 Feb 2020 17:13:08.703 * Running mode=sentinel, port=26379.
38028:X 20 Feb 2020 17:13:08.703 # WARNING: The TCP backlog setting of 511
cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value
of 128.
38028:X 20 Feb 2020 17:13:08.704 # Sentinel ID is
50547f34ed71fd48c197924969937e738a39975b
38028:X 20 Feb 2020 17:13:08.704 # +monitor master mymaster 10.0.0.8 6379 quorum
2
38028:X 20 Feb 2020 17:13:08.709 * +slave slave 10.0.0.28:6379 10.0.0.28 6379 @
mymaster 10.0.0.8 6379
38028:X 20 Feb 2020 17:13:08.709 * +slave slave 10.0.0.18:6379 10.0.0.18 6379 @
mymaster 10.0.0.8 6379
slave的哨兵日志
[root@redis-slave1 ~]#tail -f /var/log/redis/sentinel.log
25509:X 20 Feb 2020 17:13:27.435 * Removing the pid file.
25509:X 20 Feb 2020 17:13:27.435 # Sentinel is now ready to exit, bye bye...
25572:X 20 Feb 2020 17:13:27.448 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo
25572:X 20 Feb 2020 17:13:27.448 # Redis version=5.0.3, bits=64,
commit=00000000, modified=0, pid=25572, just started
25572:X 20 Feb 2020 17:13:27.448 # Configuration loaded
25572:X 20 Feb 2020 17:13:27.448 * supervised by systemd, will signal readiness
25572:X 20 Feb 2020 17:13:27.449 * Running mode=sentinel, port=26379.
25572:X 20 Feb 2020 17:13:27.449 # WARNING: The TCP backlog setting of 511
cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value
of 128.
25572:X 20 Feb 2020 17:13:27.449 # Sentinel ID is
50547f34ed71fd48c197924969937e738a39975b
25572:X 20 Feb 2020 17:13:27.449 # +monitor master mymaster 10.0.0.8 6379 quorum
2
3.6 当前sentinel状态
在sentinel状态中尤其是最后一行，涉及到masterIP是多少，有几个slave，有几个sentinels，必须是符合全部服务器数量
[root@redis-master ~]#redis-cli -p 26379
127.0.0.1:26379> 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=3 #两个
slave,三个sentinel服务器,如果sentinels值不符合,检查myid可能冲突
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