The answer is that the target group has an insufficient number of healthy instances due to health check failures. This is the most likely cause because an Application Load Balancer returns a 503 error when it cannot route traffic to any healthy registered targets, even if the underlying EC2 instances show no CPU or memory spikes—health checks can fail due to application-level issues like a misconfigured health check path or a stuck process that doesn’t affect system metrics. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding that ALB 503 errors are a classic symptom of health check failures, not infrastructure overload, and it’s a common trap to assume high resource utilization is the culprit when metrics look normal. A quick memory tip: think “503 = zero healthy targets” to distinguish it from 504 gateway timeouts or security group misconfigurations.
DOP-C02 Monitoring and Logging Practice Question
This DOP-C02 practice question tests your understanding of monitoring and logging. 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 is running a production web application on Auto Scaling EC2 instances behind an ALB. They have enabled detailed CloudWatch metrics on the EC2 instances and enabled CloudTrail. Recently, users reported intermittent 503 errors. The operations team reviews CloudWatch dashboards but sees no spike in CPU or memory. What is the MOST likely cause of the 503 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 the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The target group has an insufficient number of healthy instances due to health check failures
Option D is correct because ALB 503 errors often indicate that the target group health checks are failing due to insufficient healthy instances, which may not cause CPU/memory spikes. Option A is wrong because CloudTrail logs API calls, not HTTP responses. Option B is wrong because if detailed monitoring were disabled, metrics would be missing, but the question says they are enabled. Option C is wrong because a misconfigured security group would cause connection timeouts, not 503 errors.
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 target group has an insufficient number of healthy instances due to health check failures
Why this is correct
ALB returns 503 when no healthy targets are available; health check failures can occur without high CPU/memory.
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.
✗
Detailed monitoring is disabled for the EC2 instances
Why it's wrong here
Detailed monitoring is enabled as stated.
✗
The security group for the ALB is misconfigured
Why it's wrong here
Security group misconfiguration would cause connection timeouts, not 503.
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 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.
Monitoring and Logging — This question tests Monitoring and Logging — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The target group has an insufficient number of healthy instances due to health check failures — Option D is correct because ALB 503 errors often indicate that the target group health checks are failing due to insufficient healthy instances, which may not cause CPU/memory spikes. Option A is wrong because CloudTrail logs API calls, not HTTP responses. Option B is wrong because if detailed monitoring were disabled, metrics would be missing, but the question says they are enabled. Option C is wrong because a misconfigured security group would cause connection timeouts, not 503 errors.
What should I do if I get this DOP-C02 question wrong?
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.
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.
Question Discussion
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