- A
Increase the minimum size of the Auto Scaling group to 10 to handle the surge without scaling down.
Why wrong: This would increase cost and does not solve the session loss on instance termination during scale-in.
- B
Disable stickiness on the ALB so that any instance can handle any request.
Why wrong: Without stickiness, sessions would be lost even without scaling, as requests are distributed randomly.
- C
Modify the application to store session data in an Amazon ElastiCache for Redis cluster instead of local ephemeral storage.
This decouples sessions from instances, making them persistent across scaling events and instance replacements.
- D
Increase the health check interval on the ALB to prevent instances from being marked unhealthy too quickly.
Why wrong: This does not address session storage; sessions are still lost when instances are terminated.
Quick Answer
The correct solution is to modify the application to store session data in an Amazon ElastiCache for Redis cluster instead of local ephemeral storage. This directly addresses the root cause of session data loss during auto scaling events: when an EC2 instance is terminated during scale-in or replacement, any session data stored on its ephemeral storage is permanently lost, even with ALB stickiness enabled. On the SAP-C02 exam, this scenario tests your understanding of stateless application design and the pitfalls of relying on instance-local state for stateful workloads. A common trap is assuming that increasing the minimum instance count or adjusting health checks will prevent data loss, but these measures do not decouple session persistence from the instance lifecycle. The key insight is that ElastiCache provides a centralized, durable session store that survives scaling events, ensuring users remain logged in and their shopping carts are preserved. Memory tip: think “state should never live on the instance—keep it in a cache.”
SAP-C02 Continuous Improvement for Existing Solutions Practice Question
This SAP-C02 practice question tests your understanding of continuous improvement for existing solutions. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 critical e-commerce platform on AWS. The application consists of an Application Load Balancer (ALB) that distributes traffic to an Auto Scaling group of EC2 instances running a web server. The web servers store session data locally on the instance's ephemeral storage. The Auto Scaling group is configured with a min of 2, max of 10, and desired of 2. Recently, during a flash sale, traffic surged and the Auto Scaling group scaled out to 10 instances. However, many users reported that their shopping carts were lost and they were logged out during the event. The Cognito user pool was used for authentication, and the application uses cookies to maintain session state. The ALB's stickiness is enabled. The team observed that the ALB's RequestCountPerTarget metric was well below the instance's capacity, but the error rate increased. The CloudWatch logs show that the web server returned 503 errors for a subset of requests. After the flash sale ended, the Auto Scaling group scaled back to 2 instances, and the issue disappeared. The team wants to prevent this from happening in future events. Which solution should the Solutions Architect recommend?
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
Modify the application to store session data in an Amazon ElastiCache for Redis cluster instead of local ephemeral storage.
Option A is correct. The root cause is that session data stored on ephemeral storage is lost when instances are terminated or replaced. Even with ALB stickiness, if an instance is scaled in (terminated) or replaced, the session data is gone. Using ElastiCache for session storage decouples sessions from instances, ensuring persistence across scaling events. Option B is wrong because increasing the min size does not solve the data loss; sessions are still lost on instance termination. Option C is wrong because disabling stickiness would make it worse, as requests would go to different instances, potentially losing sessions even without scaling. Option D is wrong because increasing health check interval does not solve the data loss; it only delays detection of unhealthy instances.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the minimum size of the Auto Scaling group to 10 to handle the surge without scaling down.
Why it's wrong here
This would increase cost and does not solve the session loss on instance termination during scale-in.
- ✗
Disable stickiness on the ALB so that any instance can handle any request.
Why it's wrong here
Without stickiness, sessions would be lost even without scaling, as requests are distributed randomly.
- ✓
Modify the application to store session data in an Amazon ElastiCache for Redis cluster instead of local ephemeral storage.
Why this is correct
This decouples sessions from instances, making them persistent across scaling events and instance replacements.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
Increase the health check interval on the ALB to prevent instances from being marked unhealthy too quickly.
Why it's wrong here
This does not address session storage; sessions are still lost when instances are terminated.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
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Continuous Improvement for Existing Solutions — study guide chapter
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FAQ
Questions learners often ask
What does this SAP-C02 question test?
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Modify the application to store session data in an Amazon ElastiCache for Redis cluster instead of local ephemeral storage. — Option A is correct. The root cause is that session data stored on ephemeral storage is lost when instances are terminated or replaced. Even with ALB stickiness, if an instance is scaled in (terminated) or replaced, the session data is gone. Using ElastiCache for session storage decouples sessions from instances, ensuring persistence across scaling events. Option B is wrong because increasing the min size does not solve the data loss; sessions are still lost on instance termination. Option C is wrong because disabling stickiness would make it worse, as requests would go to different instances, potentially losing sessions even without scaling. Option D is wrong because increasing health check interval does not solve the data loss; it only delays detection of unhealthy instances.
What should I do if I get this SAP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
About these practice questions
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Same concept, more angles
1 more ways this is tested on SAP-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 runs a stateless web application on EC2 instances behind an Application Load Balancer (ALB). During peak traffic, some instances become unhealthy and are replaced by Auto Scaling, but users experience errors. What is the MOST likely cause?
hard- A.The EC2 instances are of a burstable performance type.
- B.The Auto Scaling group's minimum size is too small.
- ✓ C.The health check target path or port is misconfigured.
- D.The health check interval is too long.
Why C: Option C is correct because if the health check target is misconfigured (e.g., wrong path or port), healthy instances may be marked as unhealthy, causing unnecessary replacements and errors. Option A is wrong because a longer health check interval would reduce unnecessary replacements. Option B is wrong because instance type does not directly affect health checks. Option D is wrong because a smaller Auto Scaling group might cause capacity issues but not necessarily errors due to unhealthy instances.
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Last reviewed: Jun 20, 2026
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