sentinel是运行在特殊模式下的redis服务器，redis3.0以前的集群一般都是借助哨兵sentinel工具来监控master节点的状态，如果master节点一场，则会进行 主备切换，将slave节点升级为master节点，性能和高可用方面表现一般，特别是在主从切换瞬间

　　| sentinel对节点的判断

　　主观下线：

　　某个sentinel节点认为(info命令)某个redis节点为不可用状态

　　客观下线：

　　多个sentinel认为某个redis节点为主观下线状态，将redis节点判断为客观下线，并发起一次针对主服务器的故障转移操作

　 　| 工作原理

• 　　sentinel读入用户指定的配置文件，为每个要被监视的redis节点创建相应的实例结构，并创建连向sentinel的命令连接(用于sentinel连接redis，向redis发送命令请求)和订阅连接(用于接收sentinel:hello频道消息)
• 　　每10秒每个sentinel对redis master和slave执行info replication命令，该命令用来确认主从关系和发现slave节点
• 　　每2秒每个sentinel向redis节点的sentinel:hello频道发送消息，并根据这些信息为其他sentinel创建相应的实例结构，以及命令连接
• 　　每1秒每个sentinel对其他sentinel和redis执行ping命令，用于心跳检测

　　多主多从架构图

　　环境准备

　　| 环境介绍

　　| redis配置文件

# 与redis-master112节点部署cat > /oldboyedu/softwares/redis/redis.conf <<EOF
port 6379daemonize yes
pidfile "/oldboyedu/data/redis/redis.pid"loglevel notice
logfile "/oldboyedu/data/redis/redis.log"dbfilename "dump.rdb"dir "/oldboyedu/data/redis"requirepass "oldboyedu"masterauth "oldboyedu"bind 10.0.0.112 127.0.0.1# 配置RDB持久化策略save 900 1save 300 10save 60 10000# 配置AOF持久化appendonly yes
appendfsync everysec
EOF# 与redis-slave113节点部署cat > /oldboyedu/softwares/redis/redis.conf <<EOF
port 6379daemonize yes
pidfile "/oldboyedu/data/redis/redis.pid"loglevel notice
logfile "/oldboyedu/data/redis/redis.log"dbfilename "dump.rdb"dir "/oldboyedu/data/redis"requirepass "oldboyedu"masterauth "oldboyedu"bind 10.0.0.113 127.0.0.1# 配置RDB持久化策略save 900 1save 300 10save 60 10000# 配置AOF持久化appendonly yes
appendfsync everysec
EOF# 与redis-slave114节点部署cat > /oldboyedu/softwares/redis/redis.conf <<EOF
port 6379daemonize yes
pidfile "/oldboyedu/data/redis/redis.pid"loglevel notice
logfile "/oldboyedu/data/redis/redis.log"dbfilename "dump.rdb"dir "/oldboyedu/data/redis"requirepass "oldboyedu"masterauth "oldboyedu"bind 10.0.0.114 127.0.0.1# 配置RDB持久化策略save 900 1save 300 10save 60 10000# 配置AOF持久化appendonly yes
appendfsync everysec
EOF

　　| 启动服务

# 全部节点执行redis-server /oldboyedu/softwares/redis/redis.conf# slave节点执行redis-cli -p 6379 -a oldboyedu SLAVEOF 10.0.0.112 6379

　　部署多sentinel实例

　　| 部署sentinel实例

# 全部节点执行mkdir -pv /oldboyedu/softwares/redis26379
mkdir -pv /oldboyedu/data/redis26379
mkdir -pv /oldboyedu/logs/redis26379

　　| 创建配置文件

　　redis-master112主机

cat > /oldboyedu/softwares/redis26379/sentinel.conf <<EOF
bind 10.0.0.112 127.0.0.1port 26379dir /oldboyedu/data/redis26379
sentinel monitor mymaster 10.0.0.112 6379 2sentinel down-after-milliseconds mymaster 5000sentinel auth-pass mymaster oldboyedu
EOF

　　redis-slave113

cat > /oldboyedu/softwares/redis26379/sentinel.conf <<EOF
bind 10.0.0.113 127.0.0.1port 26379dir /oldboyedu/data/redis26379
sentinel monitor mymaster 10.0.0.112 6379 2sentinel down-after-milliseconds mymaster 5000sentinel auth-pass mymaster oldboyedu
EOF

　　redis-slave114

cat > /oldboyedu/softwares/redis26379/sentinel.conf <<EOF
bind 10.0.0.114 127.0.0.1port 26379dir /oldboyedu/data/redis26379
sentinel monitor mymaster 10.0.0.112 6379 2sentinel down-after-milliseconds mymaster 5000sentinel auth-pass mymaster oldboyedu
EOF

　　| 启动sentinel进程

# 全部节点执行redis-sentinel /oldboyedu/softwares/redis26379/sentinel.conf &> /oldboyedu/logs/redis26379/sentinel.log &

　　| 启动sentinel进程

　　验证Redis是否能够自动切换

　　| 手动停止主库运行，模拟主库宕机

主库上查看当前主从状态# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:master
connected_slaves:2slave0:ip=10.0.0.113,port=6379,state=online,offset=84,lag=0slave1:ip=10.0.0.114,port=6379,state=online,offset=70,lag=1master_failover_state:no-failover
master_replid:ba904226d8ed537c4e1b187e0db1deb5df9b68f8
master_replid2:0000000000000000000000000000000000000000master_repl_offset:84second_repl_offset:-1repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:1repl_backlog_histlen:84停止主库运行# redis-cli -p 6379 -a oldboyedu SHUTDOWN

　　| 当主库宕机后，会有其他salve来接管

redis-slave113服务器# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:master
connected_slaves:0master_failover_state:no-failover
master_replid:94676467400ce842b85705c7ee808db640008085master_replid2:e703f7e7877e9b78659b236caa9eeedc457c8f83
master_repl_offset:3710second_repl_offset:3711repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:1repl_backlog_histlen:3710redis-slave114服务器# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:slave
master_host:10.0.0.113master_port:6379master_link_status:up
master_last_io_seconds_ago:1master_sync_in_progress:0slave_repl_offset:4543slave_priority:100slave_read_only:1replica_announced:1connected_slaves:0master_failover_state:no-failover
master_replid:94676467400ce842b85705c7ee808db640008085master_replid2:e703f7e7877e9b78659b236caa9eeedc457c8f83
master_repl_offset:4543second_repl_offset:3711repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:1repl_backlog_histlen:4543

　　| 恢复master112

　　会自动加入集群并成为slave角色

# redis-server /oldboyedu/softwares/redis/redis.conf# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:slave
master_host:10.0.0.113master_port:6379master_link_status:up
master_last_io_seconds_ago:1master_sync_in_progress:0slave_repl_offset:15166slave_priority:100slave_read_only:1replica_announced:1connected_slaves:0master_failover_state:no-failover
master_replid:94676467400ce842b85705c7ee808db640008085master_replid2:0000000000000000000000000000000000000000master_repl_offset:15166second_repl_offset:-1repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:13929repl_backlog_histlen:1238

　　 验证sentinel是否为高可用

　　手动停掉任意一个sentinel实例，再次验证主从结构能否正常使用

　　| 将redis-master112的sentinel实例停用

# netstat -untalp | grep 26379 | grep LISTENtcp        0      0 127.0.0.1:26379         0.0.0.0:*               LISTEN      1162/redis-sentinel 
tcp        0      0 10.0.0.112:26379        0.0.0.0:*               LISTEN      1162/redis-sentinel# kill -9 1162[1]+  Killed                  redis-sentinel /oldboyedu/softwares/redis26379/sentinel.conf &>/oldboyedu/logs/redis26379/sentinel.log

　　| 发现依旧是可以正常切换主从的

因为做上面的实验时，master节点转移到slave113服务器上了，所以以下操作为在slave113服务器执行# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:master
connected_slaves:2slave0:ip=10.0.0.114,port=6379,state=online,offset=64400,lag=1slave1:ip=10.0.0.112,port=6379,state=online,offset=64414,lag=0master_failover_state:no-failover
master_replid:94676467400ce842b85705c7ee808db640008085master_replid2:e703f7e7877e9b78659b236caa9eeedc457c8f83
master_repl_offset:64414second_repl_offset:3711repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:1repl_backlog_histlen:64414# redis-cli -p 6379 -a oldboyedu SHUTDOWNWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.Could not connect to Redis at 127.0.0.1:6379: Connection refused

　　| master节点转移到master112服务器上了

在master112服务器上执行# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:master
connected_slaves:1slave0:ip=10.0.0.114,port=6379,state=online,offset=94729,lag=1master_failover_state:no-failover
master_replid:46266625c5a45935c25e0dc3a6121e481cc23e77master_replid2:94676467400ce842b85705c7ee808db640008085master_repl_offset:94864second_repl_offset:78055repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:13929repl_backlog_histlen:80936

　　| 恢复slave113节点

redis-server /oldboyedu/softwares/redis/redis.conf

　　| 额外停掉一台sentinel，发现不能正常切换主从

　　因为目前只有一个sentinel存活，尽管它能进行投票也只能投递1票

# netstat -untalp | grep 26379 | grep LISTENtcp        0      0 127.0.0.1:26379         0.0.0.0:*               LISTEN      1178/redis-sentinel 
tcp        0      0 10.0.0.113:26379        0.0.0.0:*               LISTEN      1178/redis-sentinel# kill -9 1178[1]+  Killed                  redis-sentinel /oldboyedu/softwares/redis26379/sentinel.conf &>/oldboyedu/logs/redis26379/sentinel.log

　　发现不能正常切换主从

　　因为目前只有一个sentinel存活，尽管它能进行投票也只能投递1票，无法我们在配置文件中定义的"sentinel monitor mymaster 10.0.0.112 6379 2"中的"2"

　　由此可以看出，主节点并未发送改变

停掉redis-master112节点的redis运行# redis-cli -p 6379 -a oldboyedu SHUTDOWNWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.于redis-slave113节点查看# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:slave
master_host:10.0.0.112master_port:6379master_link_status:down
master_last_io_seconds_ago:-1master_sync_in_progress:0slave_repl_offset:148032master_link_down_since_seconds:55slave_priority:100slave_read_only:1replica_announced:1connected_slaves:0master_failover_state:no-failover
master_replid:46266625c5a45935c25e0dc3a6121e481cc23e77master_replid2:0000000000000000000000000000000000000000master_repl_offset:148032second_repl_offset:-1repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:124049repl_backlog_histlen:23984于redis-slave114节点查看# redis-cli -p 6379 -a oldboyedu INFO REPLICATIONWarning: Using a password with '-a' or '-u' option on the command line interface may not be safe.# Replicationrole:slave
master_host:10.0.0.112master_port:6379master_link_status:down
master_last_io_seconds_ago:-1master_sync_in_progress:0slave_repl_offset:148032master_link_down_since_seconds:58slave_priority:100slave_read_only:1replica_announced:1connected_slaves:0master_failover_state:no-failover
master_replid:46266625c5a45935c25e0dc3a6121e481cc23e77master_replid2:94676467400ce842b85705c7ee808db640008085master_repl_offset:148032second_repl_offset:78055repl_backlog_active:1repl_backlog_size:1048576repl_backlog_first_byte_offset:1repl_backlog_histlen:148032