- A
The task definition's startup command is failing, causing the tasks to never become healthy.
Why wrong: Health checks are intermittent, so tasks are starting but may be slow.
- B
The ECS service is not configured with auto scaling to handle the increased traffic.
Why wrong: CPU and memory are below 50%, so scaling is not needed.
- C
The ALB idle timeout is set too low, causing connections to be closed before the application responds.
A low idle timeout can cause the ALB to close connections prematurely, resulting in 502 errors.
- D
The security group for the ECS tasks is blocking traffic from the ALB.
Why wrong: If blocked, health checks would always fail, not intermittently.
Question 831 of 1,616
DVA-C02 ALB idle timeout 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. A key principle to apply: aLB idle timeout. 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 critical application on Amazon ECS with Fargate. The application uses an Application Load Balancer (ALB) to distribute traffic. Recently, the company noticed that the ALB returns 502 Bad Gateway errors during peak traffic hours. The developer checks the ECS service metrics and sees that the number of running tasks remains constant, while CPU and memory utilization are below 50%. The ALB target group health checks are failing intermittently for some tasks. What is the MOST likely cause of the 502 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.
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 ALB idle timeout is set too low, causing connections to be closed before the application responds.
The correct answer is C because the ALB idle timeout determines how long the load balancer waits for a response from the target before closing the connection. If the application takes longer to respond than the timeout setting, the ALB terminates the connection and returns a 502 Bad Gateway error. The intermittent health check failures occur because some tasks may respond within the timeout while others do not, especially during peak traffic when processing times increase. Option A is incorrect because if the startup command were failing, tasks would never become healthy and health checks would consistently fail. Option B is incorrect because CPU and memory utilization below 50% indicate the tasks have spare capacity, so auto scaling would not resolve the latency issue. Option D is incorrect because if the security group were blocking traffic, health checks would consistently fail, not intermittently.
Key principle: ALB idle timeout
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 task definition's startup command is failing, causing the tasks to never become healthy.
Why it's wrong here
Health checks are intermittent, so tasks are starting but may be slow.
- ✗
The ECS service is not configured with auto scaling to handle the increased traffic.
Why it's wrong here
CPU and memory are below 50%, so scaling is not needed.
- ✓
The ALB idle timeout is set too low, causing connections to be closed before the application responds.
Why this is correct
A low idle timeout can cause the ALB to close connections prematurely, resulting in 502 errors.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
ALB idle timeout
- ✗
The security group for the ECS tasks is blocking traffic from the ALB.
Why it's wrong here
If blocked, health checks would always fail, not intermittently.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many developers assume 502 errors are caused by scaling or resource constraints, but a misconfigured ALB idle timeout is a common cause that is often overlooked.
Detailed technical explanation
How to think about this question
Treat this as a scenario question. Identify the problem, the constraint, and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- ALB idle timeout
- 502 Bad Gateway
- ECS health checks
- Target group health
TExam Day Tips
- 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
ALB idle timeout
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review aLB idle timeout, then practise related DVA-C02 questions on the same topic to reinforce the concept.
- →
Troubleshooting and Optimization — study guide chapter
Learn the concepts, then practise the questions
- →
Troubleshooting and Optimization practice questions
Targeted practice on this topic area only
- →
All DVA-C02 questions
1,616 questions across all exam domains
- →
AWS Certified Developer Associate DVA-C02 study guide
Full concept coverage aligned to exam objectives
- →
DVA-C02 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related DVA-C02 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Development with AWS Services practice questions
Practise DVA-C02 questions linked to Development with AWS Services.
Security practice questions
Practise DVA-C02 questions linked to Security.
Deployment practice questions
Practise DVA-C02 questions linked to Deployment.
Troubleshooting and Optimization practice questions
Practise DVA-C02 questions linked to Troubleshooting and Optimization.
DVA-C02 fundamentals practice questions
Practise DVA-C02 questions linked to DVA-C02 fundamentals.
DVA-C02 scenario practice questions
Practise DVA-C02 questions linked to DVA-C02 scenario.
DVA-C02 troubleshooting practice questions
Practise DVA-C02 questions linked to DVA-C02 troubleshooting.
Practice this exam
Start a free DVA-C02 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
FAQ
Questions learners often ask
What does this DVA-C02 question test?
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — ALB idle timeout.
What is the correct answer to this question?
The correct answer is: The ALB idle timeout is set too low, causing connections to be closed before the application responds. — The correct answer is C because the ALB idle timeout determines how long the load balancer waits for a response from the target before closing the connection. If the application takes longer to respond than the timeout setting, the ALB terminates the connection and returns a 502 Bad Gateway error. The intermittent health check failures occur because some tasks may respond within the timeout while others do not, especially during peak traffic when processing times increase. Option A is incorrect because if the startup command were failing, tasks would never become healthy and health checks would consistently fail. Option B is incorrect because CPU and memory utilization below 50% indicate the tasks have spare capacity, so auto scaling would not resolve the latency issue. Option D is incorrect because if the security group were blocking traffic, health checks would consistently fail, not intermittently.
What should I do if I get this DVA-C02 question wrong?
Review aLB idle timeout, then practise related DVA-C02 questions on the same topic to reinforce the concept.
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?
ALB idle timeout
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Keep practising
More DVA-C02 practice questions
- A developer is troubleshooting an AWS Lambda function that is triggered by an S3 event. The function occasionally fails…
- A developer needs to call AWS APIs from application code running on EC2. Which credential source should the AWS SDK use…
- A developer needs to allow an IAM user in a different AWS account to assume a role in the developer's account. The role…
- A developer needs to grant an IAM role in Account B read-only access to objects in an S3 bucket in Account A. The bucket…
- An API Gateway HTTP API should allow access only to users authenticated by an external OIDC provider. Which authorizer t…
- A developer needs to allow an EC2 instance to read from a DynamoDB table. Which is the best practice to grant permission…
Last reviewed: Jun 20, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.