AWS Certified DevOps Engineer – Professional (DOP-C02) — Question 297

A company runs a web application on Amazon Elastic Kubernetes Service (Amazon EKS). The company uses Amazon CloudFront to distribute the application. The company recently enabled AWS WAF. The company set up Amazon CloudWatch Logs to send logs to an aws-waf-logs log group.

The company wants a DevOps engineer to receive alerts if there are sudden changes in blocked traffic. The company does not want to receive alerts for other changes in AWS WAF log behavior. The company will tune AWS WAF rules over time.

The DevOps engineer is currently subscribed to an Amazon Simple Notification Service (Amazon SNS) topic in the environment.

Which solution will meet these requirements?

Answer options

• A. Create a CloudWatch Logs metrics filter for blocked requests on the AWS WAF log group to create a custom metric. Create a CloudWatch alarm by using CloudWatch anomaly detection and the published custom metric. Configure the alarm to notify the SNS topic to alert the DevOps engineer.
• B. Create a CloudWatch anomaly detector for the log group. Create a CloudWatch alarm by using metrics that the CloudWatch anomaly detector publishes. Use the high setting for the LogAnomalyPriority metric. Configure the alarm to go into alarm state if a static threshold of one anomaly is detected. Configure the alarm to notify the SNS topic to alert the DevOps engineer.
• C. Create a CloudWatch metrics filter for counted requests on the AWS WAF log group to create a custom metric. Create a CloudWatch alarm that activates when the sum of blocked requests in the custom metric during a period of 1 hour is greater than a static estimate for the acceptable number of blocked requests in 1 hour. Configure the alarm to notify the SNS topic to alert the DevOps engineer.
• D. Create a CloudWatch anomaly detector for the log group. Create a CloudWatch alarm by using metrics that the CloudWatch anomaly detector publishes. Use the medium setting for the LogAnomalyPriority metric. Configure the alarm to go into alarm state if a sum of anomalies over 1 hour is greater than an expected value. Configure the alarm to notify the SNS topic to alert the DevOps engineer.

Correct answer: A

Explanation

Creating a CloudWatch metric filter specifically for blocked requests isolates the desired traffic data, while CloudWatch anomaly detection dynamically adjusts to normal changes in traffic patterns over time as WAF rules are tuned. Using a general log group anomaly detector (options B and D) would capture all log pattern changes rather than focusing exclusively on blocked traffic. Option C is incorrect because it filters for counted requests instead of blocked requests and relies on a static threshold that does not adapt to WAF rule tuning.