← DOP-C02·Amazon Web Services

Question 450 of 1,750

Incident and Event Response →hardMultiple ChoiceObjective-mapped

503 Errors Due to Health Check Failure

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.

A
The application health check endpoint is returning HTTP 5xx or timing out.
Unhealthy targets cause the ALB to stop routing traffic, leading to 503 errors for users.
B
The ALB is misconfigured with an incorrect security group blocking traffic to the targets.
Why wrong: If the security group blocked traffic, all targets would be unhealthy continuously, not intermittently.
C
The ALB connection draining settings are too short, causing in-flight requests to fail.
Why wrong: Connection draining affects in-flight requests but does not cause health check failures.
D
The step scaling policy is too aggressive and is terminating instances prematurely.
Why wrong: Aggressive scaling would reduce capacity but not cause health check failures.

Full breakdown with real-world context →

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

✓

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: 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.

✓
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
Read the scenario before looking for a memorised answer.
✗
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: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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 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.

Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

Incident and Event Response — This question tests Incident and Event Response — Read the scenario before looking for a memorised answer..

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?

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?

Read the scenario before looking for a memorised answer.

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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.