A company is using Amazon Macie, AWS Firewall Manager, Amazon Inspector, and AWS Shield Advanced...

AWS Shield Advanced is the AWS-native managed service specifically designed to provide detection, mitigation, and visibility for Distributed Denial of Service (DDoS) attacks at both the network and application layers. Shield Advanced integrates directly with Amazon CloudWatch by publishing DDoS-related metrics such as DDoSDetected, AttackVolume, and AttackVector, which can be monitored using CloudWatch alarms to trigger alerts in near real time. This makes option D the correct and fully supported solution.

Amazon Macie focuses on discovering and protecting sensitive data (such as PII) in Amazon S3 using machine learning and does not provide DDoS detection capabilities, making option A incorrect. Amazon Inspector is a vulnerability management service that assesses EC2 instances, container images, and Lambda functions for software vulnerabilities and unintended network exposure; it does not detect live DDoS attacks, so option B is incorrect. AWS Firewall Manager is a centralized management service for configuring AWS WAF, Shield Advanced, and security groups across accounts, but it does not emit native DDoS detection metrics for alerting, which eliminates option C.

According to AWS Security Specialty documentation, the recommended best practice for DDoS detection and alerting is to enable AWS Shield Advanced and configure Amazon CloudWatch alarms on Shield metrics, optionally integrating with Amazon SNS for notifications and AWS Incident Manager for response automation.