SAP-C02 Design for New Solutions Practice Question
A company is designing a new web application that requires a scalable, low-latency key-value store for session state. The application runs on EC2 instances in an Auto Scaling group. Which solution is the MOST cost-effective and scalable?
⚠ Common exam trap
Test-takers frequently choose DynamoDB (Option C) because it is serverless and scalable, but they overlook that for session state, an in-memory cache like Redis is more cost-effective and provides lower latency, while DynamoDB's per-request costs and higher latency make it less optimal for this specific use case.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Amazon ElastiCache for Redis.
Amazon ElastiCache for Redis provides a fully managed, in-memory key-value store that delivers ultra-low latency (sub-millisecond) for session state access. It is highly scalable, supports replication and clustering, and is more cost-effective than DynamoDB for high-throughput session workloads because it avoids per-request read/write costs and provides automatic failover for high availability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Store session state on the local instance store of each EC2 instance.
Why it's wrong here
Not durable and lost on instance termination.
- ✓
Use Amazon ElastiCache for Redis.
Why this is correct
ElastiCache Redis is optimized for low-latency key-value storage and is cost-effective.
- ✗
Store session state in Amazon DynamoDB.
Why it's wrong here
DynamoDB is a good option but less cost-effective for simple session data than ElastiCache.
- ✗
Store session state in Amazon RDS for MySQL.
Why it's wrong here
RDS is not a key-value store and has higher latency.
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