This DOP-C02 practice question tests your understanding of security and compliance. 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 web application on EC2 instances behind an Application Load Balancer (ALB). The security team requires that all traffic to the ALB must be encrypted (HTTPS) and that the ALB must only accept traffic from CloudFront. The DevOps engineer has configured CloudFront with an origin pointing to the ALB, and the ALB has a listener on port 443 with a valid SSL certificate. The engineer also added a security group rule to the ALB that allows HTTPS traffic only from CloudFront's IP ranges. However, users are reporting intermittent 503 errors. The engineer checks CloudFront logs and sees that some requests are failing with 'Origin Connect Error'. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The security group rule is using an outdated list of CloudFront IP ranges, and CloudFront has added new IP ranges that are being blocked.
CloudFront uses a large set of IP addresses that change over time. Using a security group with a static list of CloudFront IPs is not recommended because the IPs change. Instead, the ALB should use a custom header that CloudFront adds. Option A is correct: the security group blocks new CloudFront IPs not in the list. Option B (SSL mismatch) would cause a different error. Option C (timeout) would be more consistent. Option D (WAF) would return 403, not 503.
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 ALB has a Web Application Firewall (WAF) that is blocking requests from CloudFront.
Why it's wrong here
WAF returns 403 Forbidden, not 503.
✓
The security group rule is using an outdated list of CloudFront IP ranges, and CloudFront has added new IP ranges that are being blocked.
Why this is correct
CloudFront IP ranges change; using a static list is unreliable.
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 SSL certificate on the ALB is not trusted by CloudFront, causing handshake failures.
Why it's wrong here
CloudFront trusts valid certificates; it would show SSL errors, not 503.
✗
The ALB idle timeout is set too low, causing CloudFront to close connections prematurely.
Why it's wrong here
This would affect all requests, not intermittent.
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
CloudFront trusts valid certificates; it would show SSL errors, not 503.
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.
Security and Compliance — This question tests Security and Compliance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The security group rule is using an outdated list of CloudFront IP ranges, and CloudFront has added new IP ranges that are being blocked. — CloudFront uses a large set of IP addresses that change over time. Using a security group with a static list of CloudFront IPs is not recommended because the IPs change. Instead, the ALB should use a custom header that CloudFront adds. Option A is correct: the security group blocks new CloudFront IPs not in the list. Option B (SSL mismatch) would cause a different error. Option C (timeout) would be more consistent. Option D (WAF) would return 403, not 503.
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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Question Discussion
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