Amazon ElastiCache for Redis
ElastiCache for Redis User Guide (API Version 2015-02-02)

Scaling Redis (cluster mode disabled) Clusters

Redis (cluster mode disabled) clusters can be a single-node cluster with 0 shards or multi-node clusters with 1 shard. Single-node clusters use the one node for both reads and writes. Multi-node clusters always have 1 node as the read/write primary node with 0 to 5 read-only replica nodes.