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Question 614 of 1,740

Monitoring and Logging →hardMultiple SelectObjective-mapped

Quick Answer

The answer is to observe the ALB's UnhealthyHostCount metric and check target group health checks, because these two steps directly address the root cause of intermittent 503 errors when RequestCount drops but ActiveConnectionCount stays steady. The UnhealthyHostCount metric reveals whether targets are failing health checks, causing the ALB to stop routing traffic to them, which explains the sudden RequestCount drop as fewer healthy hosts are available to serve requests. Meanwhile, checking target group health check configurations and logs helps identify why hosts are marked unhealthy—such as failing HTTP response codes or timeouts—which often triggers 503 errors when the ALB has no healthy targets to forward requests to. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your ability to correlate ALB metrics with health check behavior, a common trap being to focus only on access logs or instance-level logs without first verifying target group status. A useful memory tip is "drop in requests, steady connections: check health check reflections," reminding you that a RequestCount drop with steady connections usually points to unhealthy hosts rather than a traffic decline.

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 runs a web application on Amazon EC2 instances behind an Application Load Balancer. The DevOps team has enabled detailed CloudWatch metrics for the ALB and is using CloudWatch Logs for the EC2 instances. Recently, users report intermittent 503 errors. The team notices that the ALB's 'RequestCount' metric shows a sudden drop during error periods, while the 'ActiveConnectionCount' remains steady. Which TWO steps should the team take to diagnose the issue? (Choose two.)

Question 1hardmulti select

Full question →

A
Enable and analyze the ALB access logs to see the HTTP response codes and target processing time.
Access logs provide detailed per-request information, including 503 responses and which target handled the request.
B
Check the Amazon Route 53 health checks for the ALB DNS name.
Why wrong: Route 53 health checks are for DNS resolution, not ALB target health.
C
Review the EC2 instances' CloudWatch metrics for CPU utilization and network traffic.
Why wrong: These metrics may show resource constraints but not directly the cause of 503 errors.
D
Observe the ALB's 'UnhealthyHostCount' metric and check target group health checks.
Unhealthy targets cause 503 errors; this helps identify if instances are failing health checks.
E
Inspect AWS CloudTrail logs for the ALB to see if there are any configuration changes.
Why wrong: CloudTrail logs API calls, not HTTP requests or target health.

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

✓

Enable and analyze the ALB access logs to see the HTTP response codes and target processing time.

Option A is correct because ALB access logs contain detailed per-request data, including HTTP response codes (e.g., 503) and target processing time. Analyzing these logs will reveal whether the 503 errors are coming from the ALB itself (e.g., due to request queue overflow) or from the targets, and whether the sudden drop in RequestCount is due to clients aborting or the ALB throttling requests.

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 and analyze the ALB access logs to see the HTTP response codes and target processing time.
Why this is correct
Access logs provide detailed per-request information, including 503 responses and which target handled the request.
Related concept
Read the scenario before looking for a memorised answer.
✗
Check the Amazon Route 53 health checks for the ALB DNS name.
Why it's wrong here
Route 53 health checks are for DNS resolution, not ALB target health.
✗
Review the EC2 instances' CloudWatch metrics for CPU utilization and network traffic.
Why it's wrong here
These metrics may show resource constraints but not directly the cause of 503 errors.
✓
Observe the ALB's 'UnhealthyHostCount' metric and check target group health checks.
Why this is correct
Unhealthy targets cause 503 errors; this helps identify if instances are failing health checks.
Related concept
Read the scenario before looking for a memorised answer.
✗
Inspect AWS CloudTrail logs for the ALB to see if there are any configuration changes.
Why it's wrong here
CloudTrail logs API calls, not HTTP requests or target health.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often focus on EC2-level metrics (CPU, network) or CloudTrail config changes, missing that the ALB's own health check and access log data are the direct sources for diagnosing 503 errors tied to target unavailability or request queue limits.

Trap categories for this question

Command / output trap
These metrics may show resource constraints but not directly the cause of 503 errors.

Detailed technical explanation

How to think about this question

Under the hood, an ALB has a per-target surge queue (default 1024 requests) that, when full, causes the ALB to return 503s and stop accepting new requests, which explains the RequestCount drop while ActiveConnectionCount remains steady (existing connections stay open). The UnhealthyHostCount metric (Option D) directly indicates whether targets are failing health checks, which would cause the ALB to stop routing requests to them, leading to 503s and a drop in RequestCount.

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.

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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: Enable and analyze the ALB access logs to see the HTTP response codes and target processing time. — Option A is correct because ALB access logs contain detailed per-request data, including HTTP response codes (e.g., 503) and target processing time. Analyzing these logs will reveal whether the 503 errors are coming from the ALB itself (e.g., due to request queue overflow) or from the targets, and whether the sudden drop in RequestCount is due to clients aborting or the ALB throttling requests.

What should I do if I get this DOP-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.

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Same concept, more angles

1 more ways this is tested on DOP-C02

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 company runs a web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application logs show that some requests are timing out. The team needs to identify the source of the issue. Which TWO steps should they take?

hard

✓ A.Enable ALB access logs and analyze them.
B.Enable VPC Flow Logs to capture network traffic.
C.Enable AWS WAF logs to inspect HTTP requests.
✓ D.Review CloudWatch metrics for the ALB, such as 'RequestCount' and 'TargetResponseTime'.
E.Enable AWS CloudTrail to log all API calls.

Why A: Option A is correct because ALB access logs contain detailed request information. Option C is correct because CloudWatch metrics for ALB show request counts per target. Option B is wrong because CloudTrail logs API calls, not application requests. Option D is wrong because VPC Flow Logs show network traffic but not application-level details. Option E is wrong because WAF logs are for web ACLs, not general request tracing.

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