- A
Store session data in Amazon S3 and retrieve it on each request.
Why wrong: S3 has higher latency and is not suitable for frequent read/write session data.
- B
Increase the EC2 instance size to handle more sessions per instance.
Why wrong: This does not solve the problem of session sharing across instances.
- C
Use Amazon ElastiCache to store session state externally.
ElastiCache provides a fast, in-memory session store that can be accessed by all instances.
- D
Use an Amazon RDS database to store session state.
Why wrong: RDS can store session data but adds latency and cost; ElastiCache is more efficient.
Question 95 of 1,616
Why Use ElastiCache for Session State in a Horizontal Scaling Architecture
This DVA-C02 practice question tests your understanding of development with aws services. 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 company is running a monolithic application on an EC2 instance. The application currently stores session state in local memory on the instance. The company plans to scale the application horizontally by adding more instances behind a load balancer. What change is required to ensure that session state is preserved across requests?
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 to store session state externally.
Option C is correct because Amazon ElastiCache provides a managed, in-memory caching service (e.g., Redis or Memcached) that can store session state externally. By moving session data out of the EC2 instance's local memory and into a shared, low-latency data store, all instances behind the load balancer can access the same session state, ensuring persistence across requests regardless of which instance handles the request.
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.
- ✗
Store session data in Amazon S3 and retrieve it on each request.
Why it's wrong here
S3 has higher latency and is not suitable for frequent read/write session data.
- ✗
Increase the EC2 instance size to handle more sessions per instance.
Why it's wrong here
This does not solve the problem of session sharing across instances.
- ✓
Use Amazon ElastiCache to store session state externally.
Why this is correct
ElastiCache provides a fast, in-memory session store that can be accessed by all instances.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use an Amazon RDS database to store session state.
Why it's wrong here
RDS can store session data but adds latency and cost; ElastiCache is more efficient.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose Option D (RDS) because they think a database is the only reliable external store, overlooking that ElastiCache is purpose-built for high-speed, ephemeral data like session state, while RDS introduces unnecessary latency and overhead for this use case.
Detailed technical explanation
How to think about this question
ElastiCache for Redis supports built-in session management features like key expiration (TTL) and atomic operations, making it ideal for sticky-session-free architectures. Under the hood, Redis stores session data as key-value pairs in memory, allowing sub-millisecond read/write times, and can persist data to disk for durability. In a real-world scenario, a large e-commerce platform might use ElastiCache to handle millions of concurrent sessions, ensuring that a user's shopping cart persists even if the load balancer distributes requests across dozens of instances.
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 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.
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Development with AWS Services — This question tests Development with AWS Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use Amazon ElastiCache to store session state externally. — Option C is correct because Amazon ElastiCache provides a managed, in-memory caching service (e.g., Redis or Memcached) that can store session state externally. By moving session data out of the EC2 instance's local memory and into a shared, low-latency data store, all instances behind the load balancer can access the same session state, ensuring persistence across requests regardless of which instance handles the request.
What should I do if I get this DVA-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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Same concept, more angles
1 more ways this is tested on DVA-C02
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 has a Node.js application running on an EC2 instance. The application needs to store session state. The developer wants to ensure high availability and scalability by storing session data externally. Which AWS service is BEST suited for this purpose?
medium- A.Amazon DynamoDB
- B.Amazon S3
- ✓ C.Amazon ElastiCache for Redis
- D.Amazon RDS for MySQL
Why C: Amazon ElastiCache for Redis is the best choice for external session storage because it provides an in-memory data store with sub-millisecond latency, which is critical for session state access in a high-traffic Node.js application. Redis supports data structures like hashes and TTL (time-to-live) for automatic session expiration, and it can be clustered for high availability and scalability, making it ideal for stateless EC2 instances behind a load balancer.
Keep practising
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Last reviewed: Jul 4, 2026
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.
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