A session store needs an in-memory cache with persistence, replication, failover, and data structures like sorted sets for leaderboards. Which ElastiCache engine is required?
A.Memcached
Memcached lacks persistence and replication — sessions would be lost on node failure.
B.Redis OSS
Correct. Redis OSS provides persistence, failover, and sorted sets.
C.Either — they're equivalent on AWS
The engines differ significantly in capabilities; they're not interchangeable.
D.DynamoDB DAX
DAX accelerates DynamoDB reads; it isn't a general-purpose cache engine.
Why this answer
ElastiCache for Redis OSS supports persistence, replication/failover, pub/sub, and rich data structures (sorted sets, hashes). Memcached is a simpler multi-threaded in-memory cache without persistence or replication.
Correct answer: B · Last reviewed 2026-10-25
Official AWS references
Practice this interactively
Answer without seeing the solution first in the Caching & Content Delivery practice session.
Practice Caching & Content Delivery