Redis Sentinel（哨兵） 和 Master+Slave（主从）的实现和原理分析
Redis Sentinel（哨兵） 和 Master+Slave（主从）的实现和原理分析
Author QiuRiMangCao 秋日芒草
单节点
server01
server02 } redis 单节点
server03
master slave
server01
server02 } redis （master，slave）[数据备份][读写分离] slave减轻master的压力，当master挂了，slave不支持写，只支持读，所以服务还是不可用
server03
集群
server01 } { node2 （master，slave）数据备份][读写分离] slave减轻master的压力，当master挂了，slave不支持写，只支持读，所以服务还是不可用，整个节点不可用
server02 } redis { node1 （master，slave）
server03 } { node3 （master，slave）
sentinel
server01
server02 } redis （master，slave，redis-sentinel）sentinel用于切换master或slave，这样都可以写了
server03
主从配置（master，slave）
修改redis.conf 文件，设置主从配置
或者修改redis.conf文件，使用daemonize yes
./redis-server &
指定配置文件启动
./redis-server /etc/redis/6379.conf
指定端口连接
redis-cli -p 6380
启动
redis redis-server /etc/myredis/redis.config
然后再测试启动成功与否
redis-cli ping
如果不是使用脚本启动则需要使用redis-cli shutdown命令来停止
命令：
redis-cli -p 8888 shutdown
查询redis的版本信息
[root@localhost bin]# ./redis-server -v
vim 定位行
跳转到文件尾
输入冒号(:)，打开命令输入框
输入命令：$跳转到文件头
输入冒号(:)，打开命令输入框
输入命令1，是“一”的阿拉伯数字，不是小写的L
master日志信息
3311:M 20 Oct 15:37:58.872 * Ready to accept connections
3311:M 20 Oct 15:39:45.855 * Slave 127.0.0.1:1001 asks for synchronization
3311:M 20 Oct 15:39:45.855 * Full resync requested by slave 127.0.0.1:1001
3311:M 20 Oct 15:39:45.855 * Starting BGSAVE for SYNC with target: disk
3311:M 20 Oct 15:39:45.855 * Background saving started by pid 3325
3325:C 20 Oct 15:39:45.859 * DB saved on disk
3325:C 20 Oct 15:39:45.860 * RDB: 0 MB of memory used by copy-on-write
3311:M 20 Oct 15:39:45.932 * Background saving terminated with success
3311:M 20 Oct 15:39:45.933 * Synchronization with slave 127.0.0.1:1001 succeeded
slave日志信息
3321:S 20 Oct 15:39:45.854 * Connecting to MASTER 127.0.0.1:1000
3321:S 20 Oct 15:39:45.854 * MASTER <-> SLAVE sync started
3321:S 20 Oct 15:39:45.855 * Non blocking connect for SYNC fired the event.
3321:S 20 Oct 15:39:45.855 * Master replied to PING, replication can continue…
3321:S 20 Oct 15:39:45.855 * Partial resynchronization not possible (no cached master)
3321:S 20 Oct 15:39:45.855 * Full resync from master: 1a326d8a3bc1af413789dfa9dca65954072418d5:0
3321:S 20 Oct 15:39:45.933 * MASTER <-> SLAVE sync: receiving 175 bytes from master
3321:S 20 Oct 15:39:45.933 * MASTER <-> SLAVE sync: Flushing old data
3321:S 20 Oct 15:39:45.933 * MASTER <-> SLAVE sync: Loading DB in memory
3321:S 20 Oct 15:39:45.933 * MASTER <-> SLAVE sync: Finished with success
查询redis上的所有key
127.0.0.1:1000> keys *
存入master
[root@localhost redis]# ./bin/redis-cli -p 1000
127.0.0.1:1000> set password 123456
slave同步数据
[root@localhost redis]# ./bin/redis-cli -p 1001
127.0.0.1:1001> keys *
1) “password”
slave服务不让写
127.0.0.1:1001> set user:password zhangsan:123456
(error) READONLY You can’t write against a read only slave.
查看服务信息
127.0.0.1:1000> info
Server
redis_version:4.0.1
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:92e72a18d61bfe4f
redis_mode:standalone
os:Linux 3.10.0-693.el7.x86_64 x86_64
主备信息-master
# Replication
role:master #角色
connected_slaves:1
# slave0:ip=127.0.0.1,port=1001 - slave信息
slave0:ip=127.0.0.1,port=1001,state=online,offset=1084,lag=1
master_replid:1a326d8a3bc1af413789dfa9dca65954072418d5
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:1084
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:1084主备信息-slave
# Replication
role:slave
master_host:127.0.0.1
master_port:1000
master_link_status:up
master_last_io_seconds_ago:5
master_sync_in_progress:0
slave_repl_offset:1602
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:1a326d8a3bc1af413789dfa9dca65954072418d5
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:1602
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:1602memcached 和 redis的区别，redis可以缓存到硬盘，而memcached不可用
通讯过程：slave（在启动的时候会向master发送同步命令），master（将镜像数据以文件的形式同步到slave），新数据（增量[心跳]同步数据到slave），在同步数据的时候，master是非阻塞的状态，而slave是阻塞的状态，目的：防止slave在同步数据的时候，应用服务器来读取数据出现问题
主从配置（master，slave）+ redis-sentinel 高可用
redis本身不具备master-slave切换，所以要使用redis-sentinel来完成（master-slave）的自动切换
redis-sentinel可以监控扩展多个节点，就是多个（master-slave）的集群
（master-slave）的集群中slave可以多个，方便哨兵的切换到任意一个slave
sentinel配置文件在运行期间可以被多态修改，会在master服务不好用的时候将配置文件修改成slave的配置，重启sentinel会被恢复配置
sentinel在网络环境中如何知道master节点是否好用的？ 是根据互相ping - pong 来判断是否可用的
但网络还是会存在不稳定的情况，可以导致一次或多次ping不通服务器，所以sentinel会有一个规则去识别—->然后就产生了选举（投票）- 还必须满足记数才能选举出
sentinel可以有奇数个来参加选举并投票，满足一般以上挂掉整个集群就挂掉了
移动sentinel配置文件到指定目录
mv ./sentinel.conf ./sentinel
移动指定文件夹到指定目录
mv sentinel/ ../
sentinel的启动
[root@localhost bin]# ./redis-sentinel ../redis-pub/sentinel/sentinel.conf
查看sentinel和master，slave启动情况
[root@localhost bin]# ps -ef | grep redis
root 3311 1 0 15:37 ? 00:00:05 ./bin/redis-server 127.0.0.1:1000
root 3321 1 0 15:39 ? 00:00:05 ./bin/redis-server 127.0.0.1:1001
root 3336 1726 0 15:44 pts/1 00:00:00 ./bin/redis-cli -p 1000
root 3532 1802 0 16:55 pts/2 00:00:00 ./redis-sentinel *:26379 [sentinel]
root 3537 2678 0 16:56 pts/3 00:00:00 grep –color=auto redis
sentinel 启动时监控的master和slave
3532:X 20 Oct 16:55:58.458 # Sentinel ID is ddcf5dd45ac986e979558ce338948d3bc463a9d5
3532:X 20 Oct 16:55:58.458 # +monitor master mymaster 127.0.0.1 1000 quorum 1
3532:X 20 Oct 16:55:58.459 * +slave slave 127.0.0.1:1001 127.0.0.1 1001 @ mymaster 127.0.0.1 1000
配置sentinel后再去slave存入数据，还是提示失败
[root@localhost bin]# ./redis-cli -p 1001
127.0.0.1:1001> get password
“123456”
127.0.0.1:1001> set username zhaojian
(error) READONLY You can’t write against a read only slave.
停掉master：1000，并查看sentinel和slave信息
[root@localhost redis]# ./bin/redis-cli -p 1000 shutdown
[root@localhost redis]# ps -ef | grep redis
root 3321 1 0 15:39 ? 00:00:05 ./bin/redis-server 127.0.0.1:1001
root 3532 1802 0 16:55 pts/2 00:00:00 ./redis-sentinel *:26379 [sentinel]
root 3538 1373 0 17:00 pts/0 00:00:00 ./redis-cli -p 1001
root 3578 1726 0 17:02 pts/1 00:00:00 grep –color=auto redis
过配置文件中的30s后，会在启动Sentinel启动页面上输出日志信息
3532:X 20 Oct 16:55:58.455 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
3532:X 20 Oct 16:55:58.458 # Sentinel ID is ddcf5dd45ac986e979558ce338948d3bc463a9d5
3532:X 20 Oct 16:55:58.458 # +monitor master mymaster 127.0.0.1 1000 quorum 1
3532:X 20 Oct 16:55:58.459 * +slave slave 127.0.0.1:1001 127.0.0.1 1001 @ mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:11.847 # +sdown master mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:11.847 # +odown master mymaster 127.0.0.1 1000 #quorum 1/1
3532:X 20 Oct 17:03:11.847 # +new-epoch 1
3532:X 20 Oct 17:03:11.847 # +try-failover master mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:11.850 # +vote-for-leader ddcf5dd45ac986e979558ce338948d3bc463a9d5 1
3532:X 20 Oct 17:03:11.850 # +elected-leader master mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:11.850 # +failover-state-select-slave master mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:11.927 # +selected-slave slave 127.0.0.1:1001 127.0.0.1 1001 @ mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:11.927 * +failover-state-send-slaveof-noone slave 127.0.0.1:1001 127.0.0.1 1001 @ mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:11.999 * +failover-state-wait-promotion slave 127.0.0.1:1001 127.0.0.1 1001 @ mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:12.006 # +promoted-slave slave 127.0.0.1:1001 127.0.0.1 1001 @ mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:12.007 # +failover-state-reconf-slaves master mymaster 127.0.0.1 1000
3532:X 20 Oct 17:03:12.065 # +failover-end master mymaster 127.0.0.1 1000
master从1000装换到现在的1001，所以master-slave切换成功
3532:X 20 Oct 17:03:12.066 # +switch-master mymaster 127.0.0.1 1000 127.0.0.1 1001
3532:X 20 Oct 17:03:12.066 * +slave slave 127.0.0.1:1000 127.0.0.1 1000 @ mymaster 127.0.0.1 1001
3532:X 20 Oct 17:03:42.085 # +sdown slave 127.0.0.1:1000 127.0.0.1 1000 @ mymaster 127.0.0.1 1001
现在之前slave角色变为master，这就是sentinel机制的作用，已经启动监控的作用，已经将slave切换成master
# Replication
role:master
connected_slaves:0
master_replid:41997ee7b0607cda24f609821af975cd5b3c802f
master_replid2:1a326d8a3bc1af413789dfa9dca65954072418d5
master_repl_offset:32899
second_repl_offset:32900
repl_backlog_active:0
repl_backlog_size:1048576
repl_backlog_first_byte_offset:1
repl_backlog_histlen:32899现在再给1001（之前的slave）存值成功
127.0.0.1:1001> set username zhaojian
OK
现在再去连1000，会连不上
再启动1000 redis
[root@localhost bin]# ./redis-server ../redis-pub/master/redis.conf
现在1000这个已经成为slave了
# Replication
role:slave
master_host:127.0.0.1
master_port:1001
master_link_status:up
master_last_io_seconds_ago:0
master_sync_in_progress:0
slave_repl_offset:51801
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:7ad3eb737bc808a362da9b06c2943f4b35711de5
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:51801
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576
repl_backlog_first_byte_offset:32900
repl_backlog_histlen:18902因为是slave，所以不能写入
127.0.0.1:1000> keys *
1) “password”
2) “username”
127.0.0.1:1000> set age 11
(error) READONLY You can’t write against a read only slave.
总结：master和slave的配置文件没变，只是sentinel的配置文件在动态的变
查看sentinel配置文件信息
[root@localhost sentinel]# cat sentinel.conf
之前的master连接信息变成如下
sentinel myid ddcf5dd45ac986e979558ce338948d3bc463a9d5
当时配置的1000已经动态变为1001了
# Default is 30 seconds.
sentinel monitor mymaster 127.0.0.1 1001 1末尾动态增加如下，目的：是描述当前master和slave标识状态
sentinel known-slave mymaster 127.0.0.1 1000
sentinel current-epoch 1
停掉1000 和 1001 保留sentinel，之前在1001配置了slaveof 127.0.0.1 1000。
[root@localhost redis]# ./bin/redis-cli -p 1000 shutdown
[root@localhost redis]# ./bin/redis-cli -p 1001 shutdow
重新启动
[root@localhost bin]# ./redis-server ../redis-pub/master/redis.conf
[root@localhost bin]# ./redis-server ../redis-pub/slave/redis.conf
[root@localhost bin]# ps -ef | grep redis
root 3532 1802 0 16:55 pts/2 00:00:05 ./redis-sentinel *:26379 [sentinel]
root 3665 1 0 17:37 ? 00:00:00 ./redis-server 127.0.0.1:1000
root 3670 1 0 17:37 ? 00:00:00 ./redis-server 127.0.0.1:1001
root 3676 1373 0 17:37 pts/0 00:00:00 grep –color=auto redis
连接1000客户端，并查看信息
[root@localhost redis]# ./bin/redis-cli -p 1000
127.0.0.1:1000> info
重启后1000还是没从slave变成master，sentinel并没有停止，所以说明是sentinel在起作用了。
# Replication
role:slave
master_host:127.0.0.1
master_port:1001
master_link_status:up
master_last_io_seconds_ago:0
master_sync_in_progress:0
slave_repl_offset:96505
slave_priority:100
slave_read_only:1
connected_slaves:0
master_replid:8c54c599d796c83615067b1b665502a81061285a
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:96505
second_repl_offset:-1
repl_backlog_active:1
repl_backlog_size:1048576