How does the Redis Sentinel mode work?
The Redis Sentinel mode is a solution used for achieving high availability in Redis. It works by using sentinel nodes to monitor and manage the master and slave nodes in a Redis cluster, enabling automatic failover and recovery.
The specific working principle is as follows:
- When the sentinel node is started, it will specify the information of the master node to monitor and establish a connection through a configuration file or command line parameters.
- The sentinel node periodically sends PING commands to check if the master node is running normally. If the master node does not respond, the sentinel node will mark it as subjectively offline.
- When a sufficient number of sentinel nodes have marked the master node as subjectively offline, the sentinel nodes will perform a fault judgment on the master node and begin the failover operation.
- The sentinel node will elect a new master node and switch all the slave nodes to the new master node.
- The sentinel node will notify the application that a switch of the primary node has occurred.
- If the master node recovers to normal, the sentinel node will re-mark it as being subjectively online and switch the new master node back to the original master node through failover.
- Sentinel nodes can also monitor the status of slave nodes, and will respond accordingly when a slave node goes offline or recovers.
By using the sentinel mode, it is possible to achieve high availability and automatic failover in a Redis cluster, improving the reliability and stability of the system.
