Cheapest Durable Elasticache
The recommended cheapest Elasticache solution for high availability would be to set up a Redis cluster with at least 3 cache nodes in different Availability Zones within a single region. This provides both high availability and data durability, as each cache node is its own full cluster, and each node in the cluster is a separate instance running in its own Availability Zone.
Each of the 3 cache nodes in an AWS Elasticache Redis cluster acts as a full and independent cluster, storing the same data. This means that all of the cache nodes contain the same data and can be used for both read and write operations.
The cache nodes communicate with each other using a protocol called Redis Cluster, which automatically distributes data across the nodes in the cluster and ensures data consistency and availability. If one of the cache nodes fails or becomes unavailable, the remaining cache nodes will continue to function and serve client requests.
Read Replicas are not needed for durability, just for if you need a read endpoint…
Having a single cache node and a single read replica in AWS Elasticache Redis will not ensure data durability if the write node fails. In this case, the read replica would not be able to take over as the primary node and continue serving client requests.
t3 vs t4g
The new T4g instances provide better CPU performance and they are cheaper than T3 and T3a instances. This should be the go-to instance type in this instance family.
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