What is the difference between Redis Sentinel mode and Master-Slave mode?

The main differences between Redis Sentinel mode and Master-Slave mode are as follows:

1. Different functions: The master-slave mode is used for data replication and fault recovery, while the sentinel mode is used for monitoring and managing the high availability of Redis.
2. There are different roles for nodes: in master-slave mode, there are main nodes and secondary nodes, where main nodes are responsible for receiving write operations and synchronizing data to secondary nodes; in sentinel mode, there are sentinel nodes that monitor the status of main and secondary nodes, and in the event of main node failure, they elect a new main node.
3. The way of recovering from malfunctions differs: in the master-slave mode, when the master node fails, the slave nodes will automatically elect one of them as the new master node; in the sentinel mode, when the master node fails, the sentinel nodes will detect and elect a new master node, while also being able to automatically promote a slave node to become the new master node.
4. The configuration methods differ: in the master-slave mode, the relationship between the master node and the slave node needs to be manually configured; in the sentinel mode, sentinel nodes need to be configured, and they will automatically discover and manage the relationship between the master node and the slave node.
5. Different levels of high availability: In master-slave mode, a new master node needs to be elected only when the main node crashes, resulting in a temporary period of data inconsistency. In sentinel mode, sentinel nodes can promptly detect the failure of the main node and elect a new master node, thereby providing higher availability.

In conclusion, master-slave mode is mainly used for data replication and fault recovery, while sentinel mode is mainly used for monitoring and managing the high availability of Redis.