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DOP-C02 Monitoring and Logging Practice Question

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.)

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⚠ Common exam trap

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.

Correct answer & explanation

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.

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Same concept, more angles

1 more way 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 capture detailed per-request information such as request processing time, target response time, and the specific error codes (e.g., 504 Gateway Timeout) returned by the load balancer, which directly helps pinpoint whether timeouts originate at the ALB or the backend targets. Option D is correct because CloudWatch metrics for the ALB, particularly 'TargetResponseTime' and 'RequestCount', reveal latency trends and traffic patterns that indicate whether targets are slow or overloaded, helping isolate the source of the timeouts. Option B is not appropriate because VPC Flow Logs only capture IP-level metadata (source/destination, ports, accept/reject) and cannot show HTTP-layer timing or application-level errors. Option C is not appropriate because AWS WAF logs only record requests that match or are blocked by WAF rules, and the scenario does not indicate WAF is in use or that requests are being blocked. Option E is not appropriate because CloudTrail records AWS API calls for auditing, not application request behavior or latency.

JA

Written by Johnson Ajibi, MSc IT Security

Senior Network & Security Engineer · founder of Courseiva

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.