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Question 49 of 1,750

Monitoring and Logging →easyMultiple ChoiceObjective-mapped

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 DevOps engineer is troubleshooting a production issue where an Application Load Balancer (ALB) is returning 503 errors. The ALB targets are EC2 instances in an Auto Scaling group behind the ALB. The engineer checks the ALB access logs in Amazon S3 and finds that the ALB is healthy. However, the 503 errors persist. Which configuration should the engineer check next?

A
Enable AWS Shield Advanced to protect the ALB from DDoS attacks.
Why wrong: DDoS protection would not resolve a 503 error due to misconfiguration.
B
Verify that the SSL certificate associated with the ALB is not expired.
Why wrong: An expired SSL certificate would cause HTTPS errors, not 503.
C
Check the security groups for the EC2 instances to ensure they allow traffic from the ALB on the listener port.
Security groups blocking traffic from the ALB can cause 503 errors.
D
Check the ALB's target group health check settings and verify that the health check path is correct.
Why wrong: The ALB is reported as healthy, so health check settings are likely correct.

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

✓

Check the security groups for the EC2 instances to ensure they allow traffic from the ALB on the listener port.

Option C is correct because 503 errors often indicate that the ALB cannot establish a connection to the targets. The most common cause is that the security groups attached to the EC2 instances are not allowing inbound traffic from the ALB on the listener port. Option A is incorrect because AWS Shield Advanced is a DDoS protection service; the ALB being healthy in logs suggests no DDoS attack is causing the 503 errors. Option B is incorrect because an expired SSL certificate would cause different errors (e.g., 502 or handshake failures), not 503. Option D is incorrect because checking health check settings is a valid troubleshooting step, but since the engineer already verified the ALB is healthy in access logs (meaning the ALB itself is operational), the immediate next step should be to verify security groups, which are a common cause of connectivity issues.

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.

✗
Enable AWS Shield Advanced to protect the ALB from DDoS attacks.
Why it's wrong here
DDoS protection would not resolve a 503 error due to misconfiguration.
✗
Verify that the SSL certificate associated with the ALB is not expired.
Why it's wrong here
An expired SSL certificate would cause HTTPS errors, not 503.
✓
Check the security groups for the EC2 instances to ensure they allow traffic from the ALB on the listener port.
Why this is correct
Security groups blocking traffic from the ALB can cause 503 errors.
Related concept
Read the scenario before looking for a memorised answer.
✗
Check the ALB's target group health check settings and verify that the health check path is correct.
Why it's wrong here
The ALB is reported as healthy, so health check settings are likely correct.

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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

Quick reference

AWS S3 Storage Class Comparison

Storage Class	Min Duration	Retrieval	Use Case
S3 Standard	None	Immediate	Frequently accessed data
S3 Standard-IA	30 days	Immediate	Infrequent access, rapid retrieval
S3 One Zone-IA	30 days	Immediate	Non-critical infrequent data
S3 Intelligent-Tiering	None	Immediate–hours	Unknown or changing access patterns
S3 Glacier Instant	90 days	Milliseconds	Archive with instant retrieval
S3 Glacier Flexible	90 days	Minutes–hours	Archive, flexible retrieval
S3 Glacier Deep Archive	180 days	Hours	Long-term compliance archive

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.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

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: Check the security groups for the EC2 instances to ensure they allow traffic from the ALB on the listener port. — Option C is correct because 503 errors often indicate that the ALB cannot establish a connection to the targets. The most common cause is that the security groups attached to the EC2 instances are not allowing inbound traffic from the ALB on the listener port. Option A is incorrect because AWS Shield Advanced is a DDoS protection service; the ALB being healthy in logs suggests no DDoS attack is causing the 503 errors. Option B is incorrect because an expired SSL certificate would cause different errors (e.g., 502 or handshake failures), not 503. Option D is incorrect because checking health check settings is a valid troubleshooting step, but since the engineer already verified the ALB is healthy in access logs (meaning the ALB itself is operational), the immediate next step should be to verify security groups, which are a common cause of connectivity issues.

What should I do if I get this DOP-C02 question wrong?

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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