DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. 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 multi-tier web application on EC2 instances behind an Application Load Balancer. The application experiences intermittent 503 errors during peak traffic. The Auto Scaling group is configured with a step scaling policy based on CPU utilization. CloudWatch metrics show that CPU utilization never exceeds 70%, but the ALB target group reports that some targets are unhealthy. 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.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The application health check endpoint is returning HTTP 5xx or timing out.
Option A is correct because health checks are failing, causing the ALB to stop sending traffic to those instances, which results in 503 errors. The CPU utilization might be low because the unhealthy instances are not receiving traffic. Option B is wrong because if the scaling policy were too aggressive, you'd see more instances and possibly lower CPU, not 503 errors. Option C is wrong because connection draining does not cause health check failures. Option D is wrong because the application itself is failing health checks, not the ALB configuration.
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 application health check endpoint is returning HTTP 5xx or timing out.
Why this is correct
Unhealthy targets cause the ALB to stop routing traffic, leading to 503 errors for users.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The ALB is misconfigured with an incorrect security group blocking traffic to the targets.
Why it's wrong here
If the security group blocked traffic, all targets would be unhealthy continuously, not intermittently.
✗
The ALB connection draining settings are too short, causing in-flight requests to fail.
Why it's wrong here
Connection draining affects in-flight requests but does not cause health check failures.
✗
The step scaling policy is too aggressive and is terminating instances prematurely.
Why it's wrong here
Aggressive scaling would reduce capacity but not cause health check failures.
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 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 application health check endpoint is returning HTTP 5xx or timing out. — Option A is correct because health checks are failing, causing the ALB to stop sending traffic to those instances, which results in 503 errors. The CPU utilization might be low because the unhealthy instances are not receiving traffic. Option B is wrong because if the scaling policy were too aggressive, you'd see more instances and possibly lower CPU, not 503 errors. Option C is wrong because connection draining does not cause health check failures. Option D is wrong because the application itself is failing health checks, not the ALB configuration.
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", "never". 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.
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