Redis core-cluster management tool (Redis-sentinel)

Redis, as a high-performance key-value storage service, has always performed well on a single instance, but it has long been lacking in support of an official high-availability solution. As a result, Redis-sentinel came into being, providing high-availability support transparent to clients. The following article systematically explains the principle of Redis-sentinel. I hope it will be useful to you. Article

Redis, as a high-performance key-value storage service, has always performed well on a single instance, but it has long been lacking in support of an official high-availability solution. As a result, Redis-sentinel came into being, providing high-availability support transparent to clients. The following article systematically explains the principle of Redis-sentinel. I hope it will be useful to you. Article

Redis, as a high-performance key-value storage service, has always performed well on a single instance, but it has long been lacking in support of an official high-availability solution. As a result, Redis-sentinel came into being, providing high-availability support transparent to clients. The following article systematically explains the principle of Redis-sentinel. I hope it will be useful to you.

Source: www.wzxue.com

Redis-sentinel is the monitoring and management, notification, and instance failure backup service of Redis instances. It is a management tool for Redis clusters. In a general distributed central node database, Redis-sentinel is used for the work of the central node. It monitors the working conditions of other nodes and carries out fault recovery to improve the high availability of the cluster.

Redis-sentinel was completed by Redis author antirez in June this year. Because Redis instances are used in various large companies, every company needs a Redis cluster management tool, forced to write their own management tools to manage Redis clusters, antirez took into consideration the urgent needs of the community (details) and spent a few weeks writing Redis-sentinel.

Three major features of Redis-sentinel: * monitoring * notification * automatic fault recovery first, Redis-sentinel needs to establish a monitoring master list, then, the sentinels and slaves of each master in the master list are obtained for future fault recovery.

Automatic Discovery of sentinel and slave

The monitoring master of an sentinel instance is specified in the configuration file. For example, sentinel A specifies the managed master ip: port list in the configuration file, and specify the connection failure timeout time and whether the fault can be recovered. In this way, sentinel A establishes A list of monitored master nodes.

As A client, sentinel A establishes A pub/sub connection for its monitoring master 1 and A command transmission connection. The pub/sub connection aims to obtain All sentinels for monitoring master 1 through message transmission, the specific method is to subscribe"Sentinel: Hello "channel and publish host information. In this way, All sentinels that monitor master 1 subscribe to"Sentinel: Hello "channel to obtain information about other sentinels. Sentinel A creates the sentinels list of master 1. Sentinel A also uses the intermittent info command to obtain the Server Load balancer list of master 1. If the connection times out or fails, it enters the Fault Processing routine.

Fault recovery preparation

Redis-sentinel defines two states of the faulty master, O_DOWN (objectively) and S_DOWN (subobjectively ). When sentinel A fails to connect to master 1, sentinel A determines that master 1 is in subobjectively state, and then sentinel A checks and monitors the sentinels of master 1. Because A connection is established between sentinel and info commands are continuously initiated to ask and respond, after sentinel A determines that the master is 1 S_DOWN, sentinel A uses the SENTINEL IS-MASTER-DOWN-BY-ADDR command to continuously obtain the identification of other sentinel. If more than quorum (specified in the configuration) sentinel determines that master 1 has been DOWN, it determines that master 1 is O_DOWN. Then, sentinel

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A must have the can failover permission of master 1, which is also specified in the configuration file. Next, sentinel A needs to know the leader sentinel of master 1, and the leader will recover the error of master 1.

The leader sentinel of master 1 is generated by the election. Each sentinel that monitors master 1 and has the wrong recovery permission needs to make a judgment called subjective leader, that is, the leader recognized by sentinel, then, sentinel communicated the leader's identification situation through the SENTINEL IS-MASTER-DOWN-BY-ADDR command, and finally got a consensus.

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Then, the leader sentinel of master 1 starts the error recovery routine.

Troubleshooting

As the leader of master 1, sentinel A selects an slave of master 1 as the new master. Slave is selected based on a priority to determine the DNS situation. The same priority is obtained through the runid sorting. However, the priority setting has not yet been implemented, so you can directly obtain the runid sorting to get slave 1.

Then, the command slaveof no one is sent to cancel the slave status of slave 1 and convert it to the master. When the other sentinel observes that the slave becomes the master, it will know that the error handling routine is started. Sentinel A then sends it to other slave slaveof

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New-slave-ip-port command. After all slave configurations are completed, sentinel A deletes the faulty master from the monitored masters list and notifies other sentinels.

Summary

Redis-sentinel, as a cluster management tool, basically meets the requirements. However, the requirements for Redis clusters still exist. Redis cluster as the partition result, the partition configuration still requires the client or proxy protocol implementation, Redis cluster as a whole still needs a longer path. The Redis-cluster draft was launched earlier, but it has been implemented for a long time. Antriez promises to launch the Redis-cluster function in Redis 3.0.

Address: Redis-sentinel.