Quick Answer
The answer is to use ElastiCache as a centralized session store because it decouples session state from the EC2 instances, ensuring data persists independently of the Auto Scaling group’s instance lifecycle. When an instance is terminated or replaced during a scaling event, the new instance retrieves the session from ElastiCache’s in-memory cache, preventing user data loss. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of stateless architecture patterns—a core principle for Auto Scaling groups. A common trap is choosing sticky sessions (ELB session affinity), which ties state to a specific instance and fails when that instance is replaced. Instead, remember that ElastiCache provides a fast, external, and highly available store that aligns with the exam’s emphasis on fault tolerance and scalability. Memory tip: “Cache it, don’t stick it”—centralize session data outside the compute layer.
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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 runs a stateful web application on EC2 instances in an Auto Scaling group. Users report that their session data is lost when instances are replaced during scaling events. What is the best solution to preserve session state?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Use ElastiCache as a centralized session store.
ElastiCache provides fast, durable session storage.
Enable sticky sessions on the Application Load Balancer.
Why wrong: Sticky sessions do not persist across instance replacements.
Store sessions in the Application Load Balancer.
Why wrong: ALB does not store session data.
Use an S3 bucket to store session data.
Why wrong: S3 is not suitable for real-time session storage.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use ElastiCache as a centralized session store.
ElastiCache provides a centralized, in-memory session store that is external to the EC2 instances. This ensures session data persists independently of the instance lifecycle, so when an instance is replaced during a scaling event, the new instance can retrieve the session from ElastiCache, preserving user state. This is the best solution because it decouples session state from compute resources, aligning with the stateless application pattern recommended for Auto Scaling groups.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Use ElastiCache as a centralized session store.
Why this is correct
ElastiCache provides fast, durable session storage.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Enable sticky sessions on the Application Load Balancer.
Why it's wrong here
Sticky sessions do not persist across instance replacements.
Store sessions in the Application Load Balancer.
Why it's wrong here
ALB does not store session data.
Use an S3 bucket to store session data.
Why it's wrong here
S3 is not suitable for real-time session storage.
Common exam traps
The trap here is that candidates often confuse sticky sessions (option B) with session persistence, not realizing that sticky sessions only maintain request routing to the same instance, not the session data itself when the instance is replaced.
Detailed technical explanation
ElastiCache for Redis or Memcached offers sub-millisecond latency for session reads and writes, making it ideal for real-time session management. Under the hood, the application serializes session data (e.g., as JSON) and stores it with a unique session ID key; the load balancer or application sets a cookie containing that session ID, so subsequent requests can retrieve the session from the cache. In a real-world scenario, a flash sale event could trigger rapid scaling, and without ElastiCache, all in-flight sessions would be lost, causing user frustration and cart abandonment.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
The correct answer is: Use ElastiCache as a centralized session store. — ElastiCache provides a centralized, in-memory session store that is external to the EC2 instances. This ensures session data persists independently of the instance lifecycle, so when an instance is replaced during a scaling event, the new instance can retrieve the session from ElastiCache, preserving user state. This is the best solution because it decouples session state from compute resources, aligning with the stateless application pattern recommended for Auto Scaling groups.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 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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