A web tier is being made stateless so any instance can be replaced without losing user sessions. Where should session data live?
A.On each instance's local disk
Local state dies with the instance — that's stateful design.
B.In a shared ElastiCache (Redis) layer or DynamoDB
Shared external session store = stateless tier. Correct.
C.In the ALB's sticky sessions
Stickiness pins users to instances — masks statefulness rather than removing it.
D.In CloudFront edge caches
Edge cache is for content — not session state.
Why this answer
Statelessness = externalize session state to a shared store — ElastiCache for sub-millisecond access or DynamoDB for durable sessions. Sticky sessions are the OPPOSITE anti-pattern (ties users to instances); local disk loses state on instance termination.
Correct answer: B · Last reviewed 2026-11-02
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