哨兵简介
主机"宕机"
- 将宕机的 master 下线
- 找一个 slave 作为 master
- 通知所有的 slave 连接新的 master
- 启动新的 master 和 slave
- 全量复制
*N+部分复制*N
存在的问题：
- 谁来确认 master 宕机了
- 重新找一个新的 master ，怎么找法？
- 修改配置后，原来的 master 恢复了怎么办？
哨兵
哨兵(sentinal)是一个分布式系统，用于对主从结构中的每台服务器进行监控，当出现故障时通过投票机制选择新的 master 并将所有的 slave 连接到新的 master。
哨兵的作用
- 监控
- 不断的检查 master 和 slave 是否正常运行
- master 存活检测、master 与 slave 运行情况检测
- 通知（提醒）
- 自动故障转移
- 断开 master 与 slave 连接，选取一个 slave 作为 master，将其他的 slave 连接到新的 master，并告知客户端新的服务器地址
注意：
- 哨兵也是一台
redis服务器，只是不提供数据服务 - 通常哨兵配置的数量为
单数
启用哨兵模式
配置哨兵
配置一拖二的主从结构
配置三个哨兵（配置相同，端口不同）
- 参看
sentinel.conf
- 参看
启动哨兵
redis-sentinel sentinel-端口号.conf
哨兵配置项说明：
# 哨兵服务端口 port 26379 # 哨兵工作信息存储目录 dir /tmp # 监控 主 连接字符串 哨兵判挂标准（几个哨兵认定他挂了，就判定为主挂了，通常为哨兵数量的一半加一） sentinel monitor mymaster 127.0.0.1 6379 2 # 主 连接多长时间无响应，就认定它挂了（默认 30s） sentinel down-after-milliseconds mymaster 30000 # 主挂了之后，新的主上任同步数据的路线数量，数值越小，对服务器压力越小 sentinel parallel-syncs mymaster 1 # 新主同步数据时，多长时间同步完算有效 （默认 180s） sentinel failover-timeout mymaster 180000
主 redis-6379.conf
port 6379 daemonize no #logfile "6379.log" dir /redis-4.0.0/data dbfilename dump-6379.rdb rdbcompression yes rdbchecksum yes save 10 2 appendonly yes appendfsync always appendfilename appendonly-6379.aof bind 127.0.0.1 databases 16
从1 redis-6380.conf
port 6380 daemonize no #logfile "6380.log" dir /redis-4.0.0/data slaveof 127.0.0.1 6379
从2 redis-6381.conf
port 6381 daemonize no #logfile "6381.log" dir /redis-4.0.0/data slaveof 127.0.0.1 6379
哨兵1 sentinel-26379.conf
port 26379 dir /redis-4.0.0/data sentinel monitor mymaster 127.0.0.1 6379 2 sentinel down-after-milliseconds mymaster 30000 sentinel parallel-syncs mymaster 1 sentinel failover-timeout mymaster 180000
哨兵2 sentinel-26380.conf
port 26380 dir /redis-4.0.0/data sentinel monitor mymaster 127.0.0.1 6379 2 sentinel down-after-milliseconds mymaster 30000 sentinel parallel-syncs mymaster 1 sentinel failover-timeout mymaster 180000
哨兵3 sentinel-26381.conf
port 26381 dir /redis-4.0.0/data sentinel monitor mymaster 127.0.0.1 6379 2 sentinel down-after-milliseconds mymaster 30000 sentinel parallel-syncs mymaster 1 sentinel failover-timeout mymaster 180000
启动哨兵
redis-server /redis-4.0.0/conf/redis-6379.conf redis-server /redis-4.0.0/conf/redis-6380.conf redis-server /redis-4.0.0/conf/redis-6381.conf redis-sentinel /redis-4.0.0/conf/sentinel-26379.conf redis-sentinel /redis-4.0.0/conf/sentinel-26380.conf redis-sentinel /redis-4.0.0/conf/sentinel-26381.conf # 停止 主 Ctrl+C
官方原版配置文件：sentinel.conf
# Example sentinel.conf # *** IMPORTANT *** # # By default Sentinel will not be reachable from interfaces different than # localhost, either use the 'bind' directive to bind to a list of network # interfaces, or disable protected mode with "protected-mode no" by # adding it to this configuration file. # # Before doing that MAKE SURE the instance is protected from the outside # world via firewalling or other means. # # For example you may use one of the following: # # bind 127.0.0.1 192.168.1.1 # # protected-mode no # port# The port that this sentinel instance will run on port 26379 # By default Redis Sentinel does not run as a daemon. Use 'yes' if you need it. # Note that Redis will write a pid file in /var/run/redis-sentinel.pid when # daemonized. daemonize no # When running daemonized, Redis Sentinel writes a pid file in # /var/run/redis-sentinel.pid by default. You can specify a custom pid file # location here. pidfile /var/run/redis-sentinel.pid # Specify the log file name. Also the empty string can be used to force # Sentinel to log on the standard output. Note that if you use standard # output for logging but daemonize, logs will be sent to /dev/null logfile "" # sentinel announce-ip # sentinel announce-port # # The above two configuration directives are useful in environments where, # because of NAT, Sentinel is reachable from outside via a non-local address. # # When announce-ip is provided, the Sentinel will claim the specified IP address # in HELLO messages used to gossip its presence, instead of auto-detecting the # local address as it usually does. # # Similarly when announce-port is provided and is valid and non-zero, Sentinel # will announce the specified TCP port. # # The two options don't need to be used together, if only announce-ip is # provided, the Sentinel will announce the specified IP and the server port # as specified by the "port" option. If only announce-port is provided, the # Sentinel will announce the auto-detected local IP and the specified port. # # Example: # # sentinel announce-ip 1.2.3.4 # dir # Every long running process should have a well-defined working directory. # For Redis Sentinel to chdir to /tmp at startup is the simplest thing # for the process to don't interfere with administrative tasks such as # unmounting filesystems. dir /tmp # sentinel monitor # # Tells Sentinel to monitor this master, and to consider it in O_DOWN # (Objectively Down) state only if at least sentinels agree. # # Note that whatever is the ODOWN quorum, a Sentinel will require to # be elected by the majority of the known Sentinels in order to # start a failover, so no failover can be performed in minority. # # Replicas are auto-discovered, so you don't need to specify replicas in # any way. Sentinel itself will rewrite this configuration file adding # the replicas using additional configuration options. # Also note that the configuration file is rewritten when a # replica is promoted to master. # # Note: master name should not include special characters or spaces. # The valid charset is A-z 0-9 and the three characters ".-_". sentinel monitor mymaster 127.0.0.1 6379 2 # sentinel auth-pass # # Set the password to use to authenticate with the master and replicas. # Useful if there is a password set in the Redis instances to monitor. # # Note that the master password is also used for replicas, so it is not # possible to set a different password in masters and replicas instances # if you want to be able to monitor these instances with Sentinel. # # However you can have Redis instances without the authentication enabled # mixed with Redis instances requiring the authentication (as long as the # password set is the same for all the instances requiring the password) as # the AUTH command will have no effect in Redis instances with authentication # switched off. # # Example: # # sentinel auth-pass mymaster MySUPER--secret-0123passw0rd # sentinel auth-user # # This is useful in order to authenticate to instances having ACL capabilities, # that is, running Redis 6.0 or greater. When just auth-pass is provided the # Sentinel instance will authenticate to Redis using the old "AUTH " # method. When also an username is provided, it will use "AUTH ". # In the Redis servers side, the ACL to provide just minimal access to # Sentinel instances, should be configured along the following lines: # # user sentinel-user >somepassword +client +subscribe +publish \ # +ping +info +multi +slaveof +config +client +exec on # sentinel down-after-milliseconds # # Number of milliseconds the master (or any attached replica or sentinel) should # be unreachable (as in, not acceptable reply to PING, continuously, for the # specified period) in order to consider it in S_DOWN state (Subjectively # Down). # # Default is 30 seconds. sentinel down-after-milliseconds mymaster 30000 # requirepass # # You can configure Sentinel itself to require a password, however when doing # so Sentinel will try to authenticate with the same password to all the # other Sentinels. So you need to configure all your Sentinels in a given # group with the same "requirepass" password. Check the following documentation # for more info: https://redis.io/topics/sentinel # sentinel parallel-syncs # # How many replicas we can reconfigure to point to the new replica simultaneously # during the failover. Use a low number if you use the replicas to serve query # to avoid that all the replicas will be unreachable at about the same # time while performing the synchronization with the master. sentinel parallel-syncs mymaster 1 # sentinel failover-timeout # # Specifies the failover timeout in milliseconds. It is used in many ways: # # - The time needed to re-start a failover after a previous failover was # already tried against the same master by a given Sentinel, is two # times the failover timeout. # # - The time needed for a replica replicating to a wrong master according # to a Sentinel current configuration, to be forced to replicate # with the right master, is exactly the failover timeout (counting since # the moment a Sentinel detected the misconfiguration). # # - The time needed to cancel a failover that is already in progress but # did not produced any configuration change (SLAVEOF NO ONE yet not # acknowledged by the promoted replica). # # - The maximum time a failover in progress waits for all the replicas to be # reconfigured as replicas of the new master. However even after this time # the replicas will be reconfigured by the Sentinels anyway, but not with # the exact parallel-syncs progression as specified. # # Default is 3 minutes. sentinel failover-timeout mymaster 180000 # SCRIPTS EXECUTION # # sentinel notification-script and sentinel reconfig-script are used in order # to configure scripts that are called to notify the system administrator # or to reconfigure clients after a failover. The scripts are executed # with the following rules for error handling: # # If script exits with "1" the execution is retried later (up to a maximum # number of times currently set to 10). # # If script exits with "2" (or an higher value) the script execution is # not retried. # # If script terminates because it receives a signal the behavior is the same # as exit code 1. # # A script has a maximum running time of 60 seconds. After this limit is # reached the script is terminated with a SIGKILL and the execution retried. # NOTIFICATION SCRIPT # # sentinel notification-script # # Call the specified notification script for any sentinel event that is # generated in the WARNING level (for instance -sdown, -odown, and so forth). # This script should notify the system administrator via email, SMS, or any # other messaging system, that there is something wrong with the monitored # Redis systems. # # The script is called with just two arguments: the first is the event type # and the second the event description. # # The script must exist and be executable in order for sentinel to start if # this option is provided. # # Example: # # sentinel notification-script mymaster /var/redis/notify.sh # CLIENTS RECONFIGURATION SCRIPT # # sentinel client-reconfig-script # # When the master changed because of a failover a script can be called in # order to perform application-specific tasks to notify the clients that the # configuration has changed and the master is at a different address. # # The following arguments are passed to the script: # # # # is currently always "failover" # is either "leader" or "observer" # # The arguments from-ip, from-port, to-ip, to-port are used to communicate # the old address of the master and the new address of the elected replica # (now a master). # # This script should be resistant to multiple invocations. # # Example: # # sentinel client-reconfig-script mymaster /var/redis/reconfig.sh # SECURITY # # By default SENTINEL SET will not be able to change the notification-script # and client-reconfig-script at runtime. This avoids a trivial security issue # where clients can set the script to anything and trigger a failover in order # to get the program executed. sentinel deny-scripts-reconfig yes # REDIS COMMANDS RENAMING # # Sometimes the Redis server has certain commands, that are needed for Sentinel # to work correctly, renamed to unguessable strings. This is often the case # of CONFIG and SLAVEOF in the context of providers that provide Redis as # a service, and don't want the customers to reconfigure the instances outside # of the administration console. # # In such case it is possible to tell Sentinel to use different command names # instead of the normal ones. For example if the master "mymaster", and the # associated replicas, have "CONFIG" all renamed to "GUESSME", I could use: # # SENTINEL rename-command mymaster CONFIG GUESSME # # After such configuration is set, every time Sentinel would use CONFIG it will # use GUESSME instead. Note that there is no actual need to respect the command # case, so writing "config guessme" is the same in the example above. # # SENTINEL SET can also be used in order to perform this configuration at runtime. # # In order to set a command back to its original name (undo the renaming), it # is possible to just rename a command to itself: # # SENTINEL rename-command mymaster CONFIG CONFIG
到此这篇关于Redis哨兵模式介绍的文章就介绍到这了。希望对大家的学习有所帮助，也希望大家多多支持脚本之家。