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Editor to share with you the example analysis of the Sentinel mode in Redis, I believe that most people do not know much about it, so share this article for your reference, I hope you will learn a lot after reading this article, let's learn about it!

The method of master-slave switching technology is:

When the master server goes down, you need to slaveof no one the slave server to the master-slave server, which requires human intervention.

This is time-consuming and laborious, but it can also make the service unavailable for a period of time. This is not the recommended method.

More time, we give priority to the Sentinel mode, which is the current mainstream mode of enterprise applications. Redis Sentinel is a highly available implementation of Redis.

Sentinel is a tool for managing multiple Redis instances. It can monitor, notify Redis, and fail over automatically.

Basic concepts of Redis Sentinel Master-Slave replication and schematic diagram of Sentinel high availability architecture

Redis Sentinel architecture

The main functions of Redis Sentinel the main functions of Sentinel include: master node survival detection, master-slave operation detection, automatic failover and master-slave switching.

The minimum tag configuration for Redis is one host and one slave.

Redis's Sentinel system can be used to manage multiple Redis servers.

The system can perform the following four tasks:

1. Monitoring: Sentinel constantly checks whether the primary server and secondary server are running properly.

2. Notification: when there is a problem with the monitored Redis server, Sentinel will send a notification to the administrator or other application through the API script

3. Automatic failover: when the master node does not work properly, Sentinel will start the automatic failover operation. It upgrades one of the slave nodes in the master-slave relationship with the failed master node to the new master node, and points the other slave nodes to the new master node.

4. Configuration provider: in Redis Sentinel mode, when the client application is initialized, it will connect to the Sentinel node collection to obtain the information of the master node

How Redis Sentinel works

When the Sentinel node connects to the Redis instance, it creates two connections: cmd and pub/sub. Sentinel sends commands to Redis over a cmd connection and connects to other Sentinel instances on the Redis instance through pub/sub.

Commands for Sentinel to interact with Redis master and slave nodes

Each Sentinel sends a PING command per second to its known primary, secondary, and other Sentinel instances.

If an instance takes longer than the time specified by down after the last valid reply to the PING command (milliseconds), Sentinel marks the instance as subjectively offline.

If the primary server is marked as subjective logout, all Sentinel nodes of the primary server are monitored to confirm that the primary server has indeed entered the subjective logout state once a second.

If the primary server is marked as subjectively logged off, and there are enough sentinels (at least the number specified in the profile) to match this judgment within the specified time range, the primary server is marked as objective offline.

Typically, each Sentinel sends INFO commands to all its known master and slave servers every 10 seconds. When Sentinel marks the primary server as offline, the frequency at which Sentinel sends INFO commands to all secondary servers of the offline primary server will be changed from once every 10 seconds to once per second.

Sentinel and other sentinels negotiate the status of the primary node. If the primary node is in the SDOWN state, the vote automatically selects the new primary node. Point the remaining slave nodes to the new master node for data replication.

If there are not enough sentinels to allow the primary server to log out, the objective logout status of the primary server is deleted. When the primary server returns a valid reply to the PING command of Sentinel, the subjective offline state of the primary server is deleted.

Note

A robust Redis Sentinel cluster should use at least three Sentinel instances and ensure that they are placed on different computers or even in different physical areas.

Sentinel cannot guarantee strong consistency. Sentinel is supported in common client application libraries.

Sentinel requires constant testing and observation to ensure high availability

test

Create a profile

The simple configuration is as follows:

Port 16379 # Sentinel port number daemonize yessentinel monitor master 127.0.0.1 6379 1 # Monitor masterprotected-mode nologfile "/ usr/local/bin/sentinel-1/sentinel-1.log" # log file

First start redis to set up the cluster, start redis-cli, and set 6379 as master

Restart sentinel

Sudo redis-sentinel sentinel-1/sentinel.conf

Close 6379

Check the roles of the other two redis-cli

Restart 6379

View sentinel Log

Sentinel.conf description # Example sentinel.conf# * IMPORTANT * * # bind IP address # bind 127.0.0.1 192.168.1.Protection mode (whether to prohibit external links, except the bound ip address) # protected-mode no# port # the port port 2637runs on this Sentinel instance does not run as a daemon by default. If desired, you can set it to yes. When daemonize no# enables the daemon to run, Redis writes a pid file, pidfile / var/run/redis-sentinel.pid#, in / var/run/redis-sentinel.pid to specify the log file name. If the value is empty, Sentinel log standard output is forced. Under the daemon, if standard output is used for logging, the logs will be sent to / dev/nulllogfile "# sentinel announce-ip # sentinel announce-port # # the above two configuration instructions are very useful in the environment because NAT can access Sentinel externally through a non-local address. # # when announce-ip is provided, Sentinel will declare the specified IP address in the communication instead of automatically detecting the local address as usual. # # similarly, when providing announce-port is valid and not 00:00, Sentinel will announce the specified TCP port. # # these two options do not need to be used together. If only announce-ip,Sentinel is provided, the server port specified by the specified IP and "port" options will be announced. # if only announce-port,Sentinel is provided, the automatically detected local IP and designated port will be advertised. # # Example:## sentinel announce-ip 1.2.3.duration dir # every long-running process should have a clearly defined working directory. For Redis Sentinel, / tmp is its own working directory. Dir / tmp# sentinel monitor # # tells Sentinel to listen on the specified master node and determine its O_DOWN status only if at least the Sentinel agrees. # copies are automatically discovered, so you do not need to specify copies. # Sentinel itself will rewrite this configuration file and add a copy using other configuration options. Also note that when the copy is promoted to the master copy, the configuration file is overwritten. # # Note: the primary node (master) name cannot contain special characters or spaces. # valid characters can be A murz 0-9 and the three characters ". _" .sentinel monitor mymaster 127.0.0.1 6379 ". If redis is configured with a password, authentication must be configured here, otherwise the # Example:## sentinel auth-pass mymaster MySUPER--secret-0123passw0rd# sentinel down-after-milliseconds # # master node or replica cannot be automatically switched within a specified period of time and the node is considered to be in a subjective offline S_DOWN state if the master node or replica does not reply to PING within a specified period of time. # # default is 30 seconds sentinel down-after-milliseconds mymaster 3000 seconds sentinel parallel-syncs # # during failover, how many replica nodes perform data synchronization sentinel parallel-syncs mymaster synchronization sentinel failover-timeout # # specify the failover timeout (in milliseconds). It is used in a variety of ways: #-the time required to restart a failover after a previous failover has been attempted by a given Sentinel against the same primary server, twice as long as the failover timeout. # #-when a slave synchronizes data from an incorrect master to start calculating the time. Until slave is corrected to synchronize data to the correct master. # #-time required to cancel a failover that is already in progress but no configuration changes are generated # #-the maximum time it takes to configure all slaves to point to a new master when failover is in progress. # even after this timeout, slaves will still be correctly configured to point to master. # # default 3-minute sentinel failover-timeout mymaster 18000 script executes the script # # sentinel notification-script and sentinel reconfig-script are used to configure the call to notify the system administrator or to reconfigure the client after a failover. The # script executes using the following rules for error handling: # # if the script exits with "1", retry execution later (up to 10 retries at the current setting). # # if the script exits with "2" (or higher), execution will not be retried. # # if the script terminates because it receives a signal, the behavior is the same as exit code 1. # # the maximum running time of a script is 60 seconds. When this limit is reached, the script terminates with SIGKILL and retries execution. # Notification script # # sentinel notification-script # # invokes the specified notification script (for example,-sdown,-odown, etc.) for any Sentinel events generated at the warning level. # this script should notify the system administrator of a problem with the Redis system monitored by email, SMS, or any other messaging system. # # call the script with two parameters: the first is the event type, and the second is the event description. # # the script must exist and be executable in order to start sentinel when this option is provided. # # example: # # sentinel notification-script mymaster / var/redis/notify.sh# client reconfiguration script # # sentinel client-reconfig-script # # when the master server changes due to failover, you can call the script to perform application-specific tasks to notify the client that the configuration has changed and the address of the master server has changed. # # the following parameters will be passed to the script: # currently it is always a failover "failover" # is "leader" or "observer" # # parameters from-ip, from-port, to-ip, to-port are used to pass the old address of the primary server and the new address of the selected copy. # # example: # # sentinel client-reconfig-script mymaster / var/redis/reconfig.sh# security # avoid script reset. By default, yes#, SENTINEL SET will not be able to change notification-script and client-reconfig-script at run time. # this avoids a simple security issue where the client can set the script to anything and trigger a failover to execute the program. Sentinel deny-scripts-reconfig yes# REDIS command rename # in this case, you can tell Sentinel to use a different command name instead of the normal command name. # for example, if the main "mymaster" and the "CONFIG" of the related copy are all renamed to "GUESSME", I can use: # # SENTINEL rename-command mymaster CONFIG GUESSME## to set up such a configuration, it will use GUESSME every time Sentinel uses CONFIG. Note that there is actually no need to respect the command case, so writing "config guessme" in the above example is the same. # # SENTINEL SET can also be used to perform this configuration at run time. # # in order to set the command back to its original name (undo rename), you can rename the command to itself: # # SENTINEL rename-command mymaster CONFIG CONFIG is all the contents of the article "sample Analysis of Sentinel Mode in Redis". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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