The correct answer is that session data is stored locally on the EC2 instance rather than in a shared external store. This is the most likely cause of sticky sessions and session loss during deployment because a rolling update terminates old instances and launches new ones; when the instance holding a user’s sticky session is taken down, the locally stored session data disappears, breaking the affinity and logging the user out. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your understanding that sticky sessions only route traffic to the same instance—they do not make session data durable. A common trap is assuming the Application Load Balancer preserves sessions across instance replacements, but the ALB simply follows the cookie; if the target instance is gone, so is the session. Remember the key distinction: sticky sessions are about routing, not storage. Memory tip: “Sticky routes, not sticky data—store sessions externally or lose them during deploy.”
DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 behind an Application Load Balancer. The application uses sticky sessions (session affinity) based on cookies. During a deployment, the DevOps engineer notices that some users are being logged out and losing session data. The deployment uses a rolling update strategy. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The session data is stored locally on the EC2 instance, not in a shared external store.
Option D is correct because during a rolling update, old instances are terminated and new instances are launched. Sticky sessions are tied to a specific instance; when that instance is terminated, the user's session is lost if it is not shared externally. Option A is wrong because the ALB configuration remains unchanged. Option B is wrong because health checks are not the direct cause. Option C is wrong because Auto Scaling is not involved unless explicitly configured.
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.
✗
The Auto Scaling group is terminating instances before the new ones are fully ready.
Why it's wrong here
Auto Scaling termination is part of the rolling update, but the issue is session persistence.
✗
The health check interval is too long, causing the ALB to route traffic to unhealthy instances.
Why it's wrong here
Health checks do not cause session loss; they affect routing.
✗
The ALB sticky session cookie is not being generated correctly.
Why it's wrong here
Cookie generation is not affected by the deployment.
✓
The session data is stored locally on the EC2 instance, not in a shared external store.
Why this is correct
When the instance is terminated, local session data is lost, causing users to be logged out.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
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 cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
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 DOP-C02 NAT questions on configuration and troubleshooting.
Incident and Event Response — This question tests Incident and Event Response — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The session data is stored locally on the EC2 instance, not in a shared external store. — Option D is correct because during a rolling update, old instances are terminated and new instances are launched. Sticky sessions are tied to a specific instance; when that instance is terminated, the user's session is lost if it is not shared externally. Option A is wrong because the ALB configuration remains unchanged. Option B is wrong because health checks are not the direct cause. Option C is wrong because Auto Scaling is not involved unless explicitly configured.
What should I do if I get this DOP-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 DOP-C02 NAT questions on configuration and troubleshooting.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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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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 stateful web application on EC2 instances behind an Application Load Balancer. The application uses sticky sessions (session affinity) based on cookies. During a deployment, the Auto Scaling group launches new instances, but users experience session loss. What is the most likely cause?
hard
A.The Auto Scaling group's lifecycle hooks are not configured.
B.The stickiness duration is set too low.
✓ C.The target group's deregistration delay is too short.
D.The target group's health check interval is too long.
Why C: The correct answer is D. Sticky sessions are tied to the instance ID. If the ALB target group's deregistration delay is too short, the ALB may route traffic to a new instance before the session is migrated. Session stickiness duration would affect how long sessions persist on the same instance, but not cause loss during deployments. Lifecycle hooks are for custom actions. Health check thresholds affect availability.
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This DOP-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 DOP-C02 exam.
Question Discussion
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