What is the difference between Redis Sentinel and Redis Cluster?

Redis Sentinel provides high availability for a single Redis dataset — it monitors master and replica nodes, automatically promotes a replica to master if the master fails, and updates clients via a service discovery mechanism. It does NOT partition data across nodes — the entire dataset lives on one master. Redis Cluster provides both high availability and horizontal scalability by partitioning the dataset across multiple master nodes, each with its own replicas. Use Sentinel when your dataset fits on one node and you primarily need automatic failover. Use Cluster when your dataset is too large for one node or you need write throughput across multiple nodes. Sentinel is simpler to operate; Cluster adds complexity but enables true scale-out.