The answer is Amazon ElastiCache for Redis, which provides the most cost-effective and scalable session storage for ALB EC2 deployments. This is because ElastiCache for Redis operates as a distributed, in-memory data store, allowing session data to be shared across all EC2 instances behind the load balancer without coupling a user to a single instance. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of stateless application design and the trade-offs between sticky sessions, shared storage, and dedicated caching services. A common trap is choosing sticky sessions (ALB session affinity), which reduces fault tolerance by pinning a user to a specific instance, or selecting Amazon RDS, which is slower and more expensive for ephemeral session data. Remember the memory tip: "Stickiness is a single point of failure; Redis is the stateless savior."
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 solutions architect is designing a web application that will run on Amazon EC2 instances behind an Application Load Balancer (ALB). The application requires that users' session data be stored and made available across all instances. Which solution is MOST cost-effective and scalable?
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 to store session data
Amazon ElastiCache for Redis provides a distributed, in-memory cache that can store session data, is cost-effective, and scales easily. Option A (sticky sessions) couples the user to a specific instance, reducing fault tolerance. Option C (EBS) is not shared across instances. Option D (RDS) is overkill and slower for session data.
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.
✓
Use Amazon ElastiCache for Redis to store session data
Why this is correct
Redis provides a fast, shared session store that all instances can access.
Related concept
Read the scenario before looking for a memorised answer.
✗
Store session data on an Amazon EBS volume attached to each instance
Why it's wrong here
EBS volumes are not shared across instances.
✗
Store session data in an Amazon RDS database
Why it's wrong here
RDS adds latency and cost compared to an in-memory cache.
✗
Enable sticky sessions (session affinity) on the ALB
Why it's wrong here
Sticky sessions reduce availability and scalability if an instance fails.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Identify which SAP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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: Use Amazon ElastiCache for Redis to store session data — Amazon ElastiCache for Redis provides a distributed, in-memory cache that can store session data, is cost-effective, and scales easily. Option A (sticky sessions) couples the user to a specific instance, reducing fault tolerance. Option C (EBS) is not shared across instances. Option D (RDS) is overkill and slower for session data.
What should I do if I get this SAP-C02 question wrong?
Identify which SAP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is designing a new application that will run on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. The application must maintain session state. The company expects steady traffic with occasional spikes. Which solution is MOST scalable and cost-effective?
medium
A.Use sticky sessions (session affinity) on the ALB with a session cookie.
B.Use Amazon ElastiCache for Memcached to store session data.
C.Store session data in Amazon DynamoDB tables.
✓ D.Use Amazon ElastiCache for Redis to store session data externally.
Why D: ElastiCache for Redis provides a centralized, scalable session store decoupled from EC2. Option A (sticky sessions) is less scalable. Option C (ElastiCache Memcached) is also viable but Redis is preferred for persistence. Option D (DynamoDB) is more expensive for session data.
Variation 2. A company is designing a new application that will run on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. The application requires that users' session data be stored durably and with low latency. The session data is accessed frequently but is rarely updated. Which solution is MOST cost-effective?
medium
✓ A.Use ElastiCache for Redis with replication.
B.Store session data in Amazon S3 with reduced redundancy.
C.Use DynamoDB with on-demand capacity.
D.Use ElastiCache for Memcached with multiple nodes.
Why A: ElastiCache for Redis is a fast, in-memory data store suitable for session management. It provides low latency and durability via replication, and is more cost-effective than DynamoDB for this use case because DynamoDB is optimized for heavy read/write workloads and has higher cost per request. Option A is correct. Option B is incorrect because ElastiCache for Memcached is not durable. Option C is incorrect because DynamoDB is over-provisioned for this scenario. Option D is incorrect because S3 is too slow for session data.
Variation 3. A company is designing a new application that will run on Amazon EC2 instances behind an Application Load Balancer. The application needs to store session state. Which AWS service provides a fully managed, highly scalable solution for session state management?
easy
A.Amazon DynamoDB
✓ B.Amazon ElastiCache for Redis
C.Amazon S3
D.Amazon RDS for MySQL
Why B: Amazon ElastiCache for Redis is the correct choice because it provides a fully managed, in-memory data store that is ideal for session state management. Redis offers sub-millisecond latency, built-in replication, and automatic failover, making it highly scalable and durable for session data. The Application Load Balancer can be configured with stickiness (session affinity) to route requests to the same EC2 instance, but using ElastiCache for Redis decouples session state from the compute layer, enabling stateless application tiers and seamless scaling.
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Question Discussion
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