Scaling replica nodes for Redis OSS (Cluster Mode Disabled)
A Redis OSS cluster with replica nodes (called replication group in the API/CLI) provides high availability via replication that has Multi-AZ with automatic failover enabled. A cluster with replica nodes is a logical collection of up to six Redis OSS nodes where one node, the Primary, is able to serve both read and write requests. All the other nodes in the cluster are read-only replicas of the Primary. Data written to the Primary is asynchronously replicated to all the read replicas in the cluster. Because Redis OSS (cluster mode disabled) does not support partitioning your data across multiple clusters, each node in a Redis OSS (cluster mode disabled) replication group contains the entire cache dataset. Redis OSS (cluster mode enabled) clusters support partitioning your data across up to 500 shards.
To change the data capacity of your cluster you must scale it up to a larger node type, or down to a smaller node type.
To change the read capacity of your cluster, add more read replicas, up to a maximum of 5, or remove read replicas.
The ElastiCache scaling up process is designed to make a best effort to retain your existing data and requires successful Redis OSS replication. For Redis OSS clusters with replicas, we recommend that sufficient memory be made available to Redis OSS.
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