This doesn't say anything about durability

I agree that ElastiCache for Redis is not a durable KV store. But what about the phrasing? "Which solutions will meet these requirements? (Choose two.)" Solutions (plural) implies two ways to *independently* fulfill the requirements. If you're supposed to select a combination of options, it's usually phrased like this: "Which combination of solutions ..."

https://aws.amazon.com/blogs/developer/elasticache-as-an-asp-net-session-store/ Amazon ElastiCache for Redis is highly suited as a session store to manage session information such as user authentication tokens, session state, and more. Simply use ElastiCache for Redis as a fast key-value store with appropriate TTL on session keys to manage your session information. Session management is commonly required for online applications, including games, e-commerce websites, and social media platforms.

"Session storage" is not the only requirement here. It is about 'optimizing customer session management during transactions', obviously it makes sense to host customer sessions on same node to easy the session management.

Answers starting with "ChatGPT says ..." are usually wrong. In that case, B and D solve the same part of the requirement (storing session data), just B is durable (as required) while D is not durable (thus failing to meet the requirement). We still need to 'optimize customer session management'.

ElastiCache can be HA and supports replication, but it remains a cache, which is by definition not durable.

That does not say anything about durability.

Elsewhere they state: "Redis was not built to be a durable and consistent database. If you need a durable, Redis-compatible database, consider Amazon MemoryDB for Redis. Because MemoryDB uses a durable transactional log that stores data across multiple Availability Zones (AZs), you can use it as your primary database. MemoryDB is purpose-built to enable developers to use the Redis API without worrying about managing a separate cache, database, or the underlying infrastructure." https://aws.amazon.com/redis/

What about durability?

Why would sticky sessions stop applicaton from storing anything?

The opposite is true: "ElastiCache is ideally suited as a front end for AWS services like Amazon RDS and DynamoDB, providing extremely low latency for high-performance applications and offloading some of the request volume while these services (!!!) provide long-lasting data durability." ElastiCache can serve as a cache for DynamoDB and provide low latency while DynamoDB (!) provides durability.