- A
Increase the size of the EC2 instances to handle more requests.
Why wrong: Increasing instance size addresses capacity, but the issue is intermittent 503s with stable healthy host count, suggesting a timeout or configuration problem.
- B
Enable detailed CloudWatch metrics on the EC2 instances to monitor CPU and memory.
Why wrong: EC2 instance metrics monitor resource utilization, but the ALB is returning 503s even though backend hosts are healthy, so the problem is likely at the load balancer level.
- C
Enable and review the ALB access logs stored in Amazon S3 to analyze the HTTP response codes and request patterns.
ALB access logs provide detailed information about each request, including response codes, timestamps, and request paths, enabling identification of the specific requests that are failing.
- D
Increase the idle timeout setting on the ALB.
Why wrong: Increasing the idle timeout might help if requests are timing out, but the 503 errors could be due to other reasons like connection limits or application errors.
Quick Answer
The correct action is to enable and review the ALB access logs stored in Amazon S3. This is because intermittent 503 errors from an ALB, despite stable backend HealthyHostCount, typically indicate that the load balancer itself is rejecting requests—often due to request queuing, latency spikes, or connection limits—rather than a backend instance failure. Access logs capture the exact HTTP response codes, request timing, and target processing time for each request, allowing you to pinpoint which specific requests are returning 503 and whether they are caused by the ALB’s idle timeout, surge queue limits, or backend response delays. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your ability to distinguish between backend health metrics and ALB-level failures; a common trap is assuming 503s always mean unhealthy targets, but here the stable HealthyHostCount points to a configuration or capacity issue at the ALB layer. Remember: when troubleshooting intermittent 503 errors from ALB using access logs, if the backend is healthy, look at the ALB’s own limits and timeouts—access logs are your forensic tool.
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 an application that runs on Amazon EC2 instances behind an Application Load Balancer. Users report intermittent 503 errors. CloudWatch metrics for the ALB show an increase in 'HTTPCode_ELB_5XX_Count' but the backend 'HealthyHostCount' remains stable. Which action should the engineer take to identify the root cause?
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
Enable and review the ALB access logs stored in Amazon S3 to analyze the HTTP response codes and request patterns.
Option C is correct because increasing the ALB's idle timeout will not help if requests are taking longer than the timeout. Option A is wrong because it would only help if there were autoscaling issues. Option B is wrong because the backend is healthy, so the issue is likely with the ALB configuration. Option D is correct because checking ALB access logs can reveal the exact requests that are failing, allowing analysis of latency or errors.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Increase the size of the EC2 instances to handle more requests.
Why it's wrong here
Increasing instance size addresses capacity, but the issue is intermittent 503s with stable healthy host count, suggesting a timeout or configuration problem.
- ✗
Enable detailed CloudWatch metrics on the EC2 instances to monitor CPU and memory.
Why it's wrong here
EC2 instance metrics monitor resource utilization, but the ALB is returning 503s even though backend hosts are healthy, so the problem is likely at the load balancer level.
- ✓
Enable and review the ALB access logs stored in Amazon S3 to analyze the HTTP response codes and request patterns.
Why this is correct
ALB access logs provide detailed information about each request, including response codes, timestamps, and request paths, enabling identification of the specific requests that are failing.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
Increase the idle timeout setting on the ALB.
Why it's wrong here
Increasing the idle timeout might help if requests are timing out, but the 503 errors could be due to other reasons like connection limits or application errors.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
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Monitoring and Logging — study guide chapter
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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 — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Enable and review the ALB access logs stored in Amazon S3 to analyze the HTTP response codes and request patterns. — Option C is correct because increasing the ALB's idle timeout will not help if requests are taking longer than the timeout. Option A is wrong because it would only help if there were autoscaling issues. Option B is wrong because the backend is healthy, so the issue is likely with the ALB configuration. Option D is correct because checking ALB access logs can reveal the exact requests that are failing, allowing analysis of latency or errors.
What should I do if I get this DOP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related DOP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 20, 2026
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.
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