Amazon ElastiCache for Redis is the correct choice because it provides an in-memory data store with sub-millisecond latency, which is essential for session state storage in a microservices architecture on AWS ECS with Fargate. Redis supports native data structures like hashes and strings that directly map to session data patterns, and its replication with Multi-AZ failover ensures high availability without the overhead of disk-based I/O. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this question tests your understanding of stateless microservices design and the trade-off between latency and durability—a common trap is choosing Amazon DynamoDB for its managed scalability, but DynamoDB’s eventual consistency and disk-based reads introduce higher latency for session state. Remember that session state is ephemeral and requires fast reads and writes, not persistent storage. Memory tip: “Redis for rapid reads, Dynamo for durable deeds.”
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often 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.
Detailed technical explanation
How to think about this question
Redis stores data entirely in RAM, allowing O(1) operations for key lookups, and supports built-in key expiration via the EXPIRE command or TTL attribute, which is essential for session state cleanup without custom garbage collection. ElastiCache for Redis can be deployed in cluster mode with sharding across up to 500 nodes and read replicas for read-heavy workloads, ensuring sub-millisecond p99 latency even under load. In a real-world scenario, a Fargate service handling 10,000 requests per second would see Redis handle session lookups in under 1 ms, while DynamoDB would incur 5–10 ms latency and higher costs due to provisioned throughput.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design for New Solutions — This question tests Design for New Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this SAP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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