← DOP-C02·Amazon Web Services

Question 203 of 1,750

Incident and Event Response →mediumMultiple ChoiceObjective-mapped

ALB 5xx Errors from Health Check Dependency 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 containerized application on Amazon ECS with Fargate launch type. The application is behind an Application Load Balancer (ALB). The operations team notices that the ALB's 5xx error rate increases periodically. The ECS service is configured with a target tracking scaling policy based on CPU utilization. The CloudWatch logs from the application show no errors. The health check on the ALB is configured to hit the /health endpoint. What is the MOST likely cause of the 5xx errors?

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.

A
The ECS tasks are running on an underlying host that is being patched.
Why wrong: Fargate abstracts the host.
B
The health check endpoint is returning a 503 status due to a dependency failure.
If the health check fails, the ALB returns 503.
C
The target tracking scaling policy is not responding quickly enough to traffic spikes.
Why wrong: Scaling delays might cause increased latency, not 5xx.
D
The application is throwing exceptions that are not logged.
Why wrong: Logs show no errors.

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 health check endpoint is returning a 503 status due to a dependency failure.

The correct answer is B. The ALB periodically reports 5xx errors because the health check endpoint /health is returning a 503 status code, likely due to a transient dependency failure. When the health check fails, the ALB considers the target unhealthy and returns a 503 (or 502) to clients. The application code itself logs no errors because the failure occurs in a downstream dependency that the health check probes, not in the main application logic. Option A is incorrect because ECS with Fargate does not expose underlying host patching; the ALB would not detect such patching as 5xx errors. Option C is incorrect because a target tracking CPU scaling policy, even if slow, would not cause 5xx errors—it would affect performance but not directly trigger health check failures. Option D is incorrect because the application logs show no errors, ruling out unlogged exceptions as the source.

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 ECS tasks are running on an underlying host that is being patched.
Why it's wrong here
Fargate abstracts the host.
✓
The health check endpoint is returning a 503 status due to a dependency failure.
Why this is correct
If the health check fails, the ALB returns 503.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The target tracking scaling policy is not responding quickly enough to traffic spikes.
Why it's wrong here
Scaling delays might cause increased latency, not 5xx.
✗
The application is throwing exceptions that are not logged.
Why it's wrong here
Logs show no errors.

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.

Trap categories for this question

Command / output trap
Logs show no errors.

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 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. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. 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.

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 health check endpoint is returning a 503 status due to a dependency failure. — The correct answer is B. The ALB periodically reports 5xx errors because the health check endpoint /health is returning a 503 status code, likely due to a transient dependency failure. When the health check fails, the ALB considers the target unhealthy and returns a 503 (or 502) to clients. The application code itself logs no errors because the failure occurs in a downstream dependency that the health check probes, not in the main application logic. Option A is incorrect because ECS with Fargate does not expose underlying host patching; the ALB would not detect such patching as 5xx errors. Option C is incorrect because a target tracking CPU scaling policy, even if slow, would not cause 5xx errors—it would affect performance but not directly trigger health check failures. Option D is incorrect because the application logs show no errors, ruling out unlogged exceptions as the source.

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". 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.