SAP-C02 Design for New Solutions Practice Question
A company is designing a microservices architecture on AWS ECS with Fargate. Each service needs to store and retrieve session state. The solution must be highly available and low latency. Which AWS service should be used for session state storage?
⚠ Common exam trap
It's easy for candidates to choose DynamoDB because it is a managed, highly available database with low latency, but they overlook that session state is ephemeral and best served by an in-memory cache like Redis, which offers lower latency, automatic TTL expiration, and lower cost for transient data patterns.
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
✓
Amazon ElastiCache for Redis
Amazon ElastiCache for Redis is the correct choice because it provides an in-memory data store with sub-millisecond latency, ideal for session state storage in a microservices architecture. Redis supports data structures like hashes and strings that map directly to session data patterns, and its replication and cluster modes ensure high availability across multiple Availability Zones. Fargate tasks can connect to ElastiCache via private subnets, maintaining low latency without the overhead of disk-based I/O.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Amazon ElastiCache for Redis
Why this is correct
ElastiCache for Redis is an in-memory cache with sub-millisecond latency, ideal for session state.
- ✗
Amazon RDS for MySQL
Why it's wrong here
RDS is a relational database, not optimal for session state due to overhead.
- ✗
Amazon S3
Why it's wrong here
S3 is object storage with higher latency and not designed for session state.
- ✗
Amazon DynamoDB
Why it's wrong here
DynamoDB is a NoSQL database but has higher latency than ElastiCache for session state.
Visual reference
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
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