Redis Sentinel（哨兵） 和 Master+Slave（主從）的實現和原理分析
Author QiuRiMangCao 秋日芒草
單節點
server01
server02 } redis 單節點
server03
master slave
server01
server02 } redis （master，slave）[數據備份][讀寫分離] slave減輕master的壓力，當master掛了，slave不支持寫，只支持讀，所以服務還是不可用
server03
集羣
server01 } { node2 （master，slave）數據備份][讀寫分離] slave減輕master的壓力，當master掛了，slave不支持寫，只支持讀，所以服務還是不可用，整個節點不可用
server02 } redis { node1 （master，slave）
server03 } { node3 （master，slave）
sentinel
server01
server02 } redis （master，slave，redis-sentinel）sentinel用於切換master或slave，這樣都可以寫了
server03
主從配置（master，slave）
修改redis.conf 文件，設置主從配置
或者修改redis.conf文件，使用daemonize yes
./redis-server &
指定配置文件啓動
./redis-server /etc/redis/6379.conf
指定端口連接
redis-cli -p 6380
啓動
redis redis-server /etc/myredis/redis.config
然後再測試啓動成功與否
redis-cli ping
如果不是使用腳本啓動則需要使用redis-cli shutdown命令來停止
命令：
redis-cli -p 8888 shutdown
查詢redis的版本信息
[root@localhost bin]# ./redis-server -v
vim 定位行
跳轉到文件尾
輸入冒號(:)，打開命令輸入框
輸入命令：$跳轉到文件頭
輸入冒號(:)，打開命令輸入框
輸入命令1，是“一”的阿拉伯數字，不是小寫的L
master日誌信息
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日誌信息
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
查詢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同步數據
[root@localhost redis]# ./bin/redis-cli -p 1001
127.0.0.1:1001> keys *
1) “password”
slave服務不讓寫
127.0.0.1:1001> set user:password zhangsan:123456
(error) READONLY You can’t write against a read only slave.
查看服務信息
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
主備信息-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主備信息-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的區別，redis可以緩存到硬盤，而memcached不可用
通訊過程：slave（在啓動的時候會向master發送同步命令），master（將鏡像數據以文件的形式同步到slave），新數據（增量[心跳]同步數據到slave），在同步數據的時候，master是非阻塞的狀態，而slave是阻塞的狀態，目的：防止slave在同步數據的時候，應用服務器來讀取數據出現問題
主從配置（master，slave）+ redis-sentinel 高可用
redis本身不具備master-slave切換，所以要使用redis-sentinel來完成（master-slave）的自動切換
redis-sentinel可以監控擴展多個節點，就是多個（master-slave）的集羣
（master-slave）的集羣中slave可以多個，方便哨兵的切換到任意一個slave
sentinel配置文件在運行期間可以被多態修改，會在master服務不好用的時候將配置文件修改成slave的配置，重啓sentinel會被恢復配置
sentinel在網絡環境中如何知道master節點是否好用的？ 是根據互相ping - pong 來判斷是否可用的
但網絡還是會存在不穩定的情況，可以導致一次或多次ping不通服務器，所以sentinel會有一個規則去識別—->然後就產生了選舉（投票）- 還必須滿足記數才能選舉出
sentinel可以有奇數個來參加選舉並投票，滿足一般以上掛掉整個集羣就掛掉了
移動sentinel配置文件到指定目錄
mv ./sentinel.conf ./sentinel
移動指定文件夾到指定目錄
mv sentinel/ ../
sentinel的啓動
[root@localhost bin]# ./redis-sentinel ../redis-pub/sentinel/sentinel.conf
查看sentinel和master，slave啓動情況
[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 啓動時監控的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後再去slave存入數據，還是提示失敗
[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，並查看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
過配置文件中的30s後，會在啓動Sentinel啓動頁面上輸出日誌信息
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從1000裝換到現在的1001，所以master-slave切換成功
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
現在之前slave角色變爲master，這就是sentinel機制的作用，已經啓動監控的作用，已經將slave切換成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現在再給1001（之前的slave）存值成功
127.0.0.1:1001> set username zhaojian
OK
現在再去連1000，會連不上
再啓動1000 redis
[root@localhost bin]# ./redis-server ../redis-pub/master/redis.conf
現在1000這個已經成爲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因爲是slave，所以不能寫入
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.
總結：master和slave的配置文件沒變，只是sentinel的配置文件在動態的變
查看sentinel配置文件信息
[root@localhost sentinel]# cat sentinel.conf
之前的master連接信息變成如下
sentinel myid ddcf5dd45ac986e979558ce338948d3bc463a9d5
當時配置的1000已經動態變爲1001了
# Default is 30 seconds.
sentinel monitor mymaster 127.0.0.1 1001 1末尾動態增加如下，目的：是描述當前master和slave標識狀態
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
重新啓動
[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
連接1000客戶端，並查看信息
[root@localhost redis]# ./bin/redis-cli -p 1000
127.0.0.1:1000> info
重啓後1000還是沒從slave變成master，sentinel並沒有停止，所以說明是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