Replication, Sentinel and Clusters

Replication

A replica (slaveof/replicaof) copies the primary's dataset. Reads can scale to replicas, and the primary stays the write owner. Replicas also keep RDB files reused for fast handover.

Sentinel for High Availability

Sentinel watches primaries, promotes a replica when a primary fails, and routes clients to the new leader with a single connection string. It delivers automatic failover without data resharding.

Redis Cluster

Cluster mode shards keys across 16384 hash slots on multiple primaries with replicas. Clients receive MOVED/ASK redirections to the right node, enabling data volumes beyond one server's RAM.

Choosing the Tier

• Single - simplest, fits cache workloads.
• Primary + replicas - read scaling and durability.
• Sentinel - automatic failover on top.
• Cluster - horizontal sharding at scale.

Key Points

• Replicas copy and scale reads.
• Sentinel automates leader failover.
• Cluster shards keys across nodes.
• Match the tier to your consistency and size.