← DVA-C02·Amazon Web Services

Question 396 of 1,616

Troubleshooting and Optimization →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the application is not properly handling timeouts to the third-party service, causing the health check endpoint to hang. When your ECS Fargate task makes an external API call and waits indefinitely for a response, the health check endpoint on the container cannot reply to the ALB within the configured timeout interval, resulting in intermittent 503 responses. This is a classic cascading failure pattern: the health check fails, the ALB stops routing traffic, the remaining tasks get overloaded, and latency spikes further. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of how application-level dependencies directly impact infrastructure health checks—a common trap is to blame networking or CPU when the real issue is unhandled timeouts in the code. Remember the memory tip: “A hanging handler makes a failing Fargate”—if your health check endpoint hangs waiting on an external call, the ALB will see a 503.

DVA-C02 Troubleshooting and Optimization Practice Question

This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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.

An application running on Amazon ECS Fargate is experiencing intermittent high latency and timeout errors. The application makes API calls to an external third-party service. The ECS service is configured with a target group using HTTP health checks. The ALB health check logs show occasional 503 responses. 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.

Question 1hardmultiple choice

Full question →

A
The security group for the ECS tasks is blocking inbound traffic from the ALB.
Why wrong: If the security group blocked traffic, health checks would consistently fail, not intermittently.
B
The ECS tasks are running out of CPU credits, causing slow response times.
Why wrong: Fargate uses CPU shares, not credits. Insufficient CPU would cause slow performance but not specifically 503 health check failures.
C
The ECS service is configured with a task placement strategy that is causing tasks to be stopped and restarted frequently.
Why wrong: Task restarts would cause temporary unavailability but not necessarily 503 health check responses.
D
The application is not properly handling timeouts to the third-party service, causing the health check endpoint to hang.
If the health check endpoint is blocked by a long-running call to the external service, the ALB health check may timeout and return 503, leading to unhealthy tasks.

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 is not properly handling timeouts to the third-party service, causing the health check endpoint to hang.

Option A is correct because if the application is waiting for a response from the third-party service, it may not respond to health checks in time, causing the ALB to mark it unhealthy and stop routing traffic, which exacerbates the issue. Option B (insufficient CPU) could cause latency but not specifically 503s. Option C (security group) would cause consistent failures. Option D (task placement) would cause new tasks to be created, but not 503s.

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 security group for the ECS tasks is blocking inbound traffic from the ALB.
Why it's wrong here
If the security group blocked traffic, health checks would consistently fail, not intermittently.
✗
The ECS tasks are running out of CPU credits, causing slow response times.
Why it's wrong here
Fargate uses CPU shares, not credits. Insufficient CPU would cause slow performance but not specifically 503 health check failures.
✗
The ECS service is configured with a task placement strategy that is causing tasks to be stopped and restarted frequently.
Why it's wrong here
Task restarts would cause temporary unavailability but not necessarily 503 health check responses.
✓
The application is not properly handling timeouts to the third-party service, causing the health check endpoint to hang.
Why this is correct
If the health check endpoint is blocked by a long-running call to the external service, the ALB health check may timeout and return 503, leading to unhealthy tasks.
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.

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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.

What to study next

Got this wrong? Here's your next step.

Identify which DVA-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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Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

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FAQ

Questions learners often ask

What does this DVA-C02 question test?

Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The application is not properly handling timeouts to the third-party service, causing the health check endpoint to hang. — Option A is correct because if the application is waiting for a response from the third-party service, it may not respond to health checks in time, causing the ALB to mark it unhealthy and stop routing traffic, which exacerbates the issue. Option B (insufficient CPU) could cause latency but not specifically 503s. Option C (security group) would cause consistent failures. Option D (task placement) would cause new tasks to be created, but not 503s.

What should I do if I get this DVA-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 DVA-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 DVA-C02 exam.