Increasing Read Capacity
To increase read capacity, add read replicas (up to a maximum of five) to your Redis replication group.
Due to the current limitations on Redis (cluster mode enabled), to scale the number of replicas in the shards of a Redis (cluster mode enabled) cluster, you must create a new Redis (cluster mode enabled) cluster with the new number of replicas and then delete the old cluster.
You can scale your Redis cluster’s read capacity using the ElastiCache console, the AWS CLI, or the ElastiCache API. For more information, see Adding a Read Replica to a Redis Cluster.