The correct action is to review the ALB access logs to identify the target response codes. HTTP 503 errors from an Application Load Balancer mean the targets—your EC2 instances—are failing to respond successfully, often due to overload, application crashes, or health check failures. Access logs capture the exact response code returned by each target (e.g., a 503 from the instance itself versus a connection timeout), allowing you to distinguish between a saturated Auto Scaling group and a misconfigured application. On the AWS Certified Developer Associate DVA-C02 exam, this question tests your ability to diagnose load balancer issues systematically rather than jumping to scaling or health check tweaks. A common trap is assuming you should immediately increase instance count or modify health check thresholds, but the logs must be your first step to confirm the root cause. Memory tip: “503 from ALB? Log the target’s reply.”
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 EC2 instances behind an Application Load Balancer (ALB) occasionally returns HTTP 503 errors. The instances are in an Auto Scaling group. Which action should be taken to resolve this issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Review the ALB access logs to identify the target response codes.
HTTP 503 errors from an ALB indicate that the targets (EC2 instances) are not responding successfully. Reviewing ALB access logs reveals the specific target response codes (e.g., 503 from the target itself or connection timeouts), which helps pinpoint whether the issue is due to overloaded instances, application errors, or health check failures. This diagnostic step is essential before making any configuration changes.
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.
Review the ALB access logs to identify the target response codes.
Why this is correct
Access logs show whether the 503 is from targets or the ALB, guiding further action.
Related concept
Read the scenario before looking for a memorised answer.
✗
Increase the ALB idle timeout setting.
Why it's wrong here
Idle timeout affects connection persistence, not 503 errors.
✗
Increase the size of the EC2 instances.
Why it's wrong here
While helpful if overloaded, it's a guess without data; access logs should be checked first.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often jump to scaling or instance size changes (Option D) without first using access logs to diagnose whether the 503s originate from the ALB or the targets, leading to ineffective fixes.
Detailed technical explanation
How to think about this question
ALB access logs capture detailed request/response data, including the `elb_status_code` and `target_status_code` fields, which distinguish between errors generated by the ALB (e.g., 503 due to no healthy targets) and errors from the target itself. Under the hood, the ALB routes requests based on target group health checks; if all targets are marked unhealthy, the ALB returns 503 immediately. Access logs also record request timing and client IP, enabling correlation with Auto Scaling events or application performance metrics.
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.
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
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Review the ALB access logs to identify the target response codes. — HTTP 503 errors from an ALB indicate that the targets (EC2 instances) are not responding successfully. Reviewing ALB access logs reveals the specific target response codes (e.g., 503 from the target itself or connection timeouts), which helps pinpoint whether the issue is due to overloaded instances, application errors, or health check failures. This diagnostic step is essential before making any configuration changes.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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 →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A web application running on EC2 instances behind an Application Load Balancer (ALB) is experiencing intermittent 503 errors. The ALB target group health checks are succeeding. Which step should the developer take FIRST to diagnose the issue?
medium
A.Increase the number of EC2 instances in the target group.
✓ B.Examine the ALB access logs for 503 responses.
C.Check the Route 53 record for the ALB.
D.Verify that the EC2 instances are in a running state.
Why B: Option D is correct because examining ALB access logs can reveal the response status codes and request details. Option A is wrong because health checks succeed. Option B is wrong because increasing instances may not address the root cause. Option C is wrong because the issue is with the ALB, not DNS.
Variation 2. An application uses an Application Load Balancer (ALB) with a target group of EC2 instances. Users report intermittent HTTP 503 errors. The ALB access logs show that the error occurs when the request rate exceeds 10,000 requests per second. What is the most likely cause?
hard
A.The EC2 instances are failing health checks.
B.The SSL certificate is expiring.
✓ C.The ALB is exceeding its connection limit.
D.The target group's connection draining is too short.
Why C: Option A is correct because ALB has a default limit of 10,000 new connections per second (which may be lower depending on region) and exceeding it causes 503 errors. Option B is wrong because connection draining is a graceful shutdown, not causing errors. Option C is wrong because the instances are healthy. Option D is wrong because the issue is not SSL negotiation.
Last reviewed: Jun 24, 2026
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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.
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