A company stores its processed data in an S3 bucket. The company has a strict data access policy. The company uses IAM roles to grant teams within…

AWS CloudTrail is the appropriate service for auditing API activity. By enabling data events for the S3 bucket, all object-level API calls (like GetObject, PutObject, DeleteObject) are logged. These logs include the userIdentity element, which contains details about the principal that made the request, such as the username or assumed role. These detailed logs can be sent to Amazon CloudWatch Logs. In CloudWatch, you can create metric filters to search for specific patterns, such as AccessDenied errors, and configure alarms to send notifications when these patterns are detected, thus meeting all requirements.

A. AWS Config tracks resource configuration changes, not real-time API access violations by users. It is unsuitable for this use case.
B. Amazon CloudWatch metrics for S3 are aggregated and do not provide user-level details needed to identify a specific user violating a policy.
D. S3 server access logs are delivered on a best-effort basis and are not real-time. CloudTrail is the recommended service for security auditing and compliance.

1. AWS CloudTrail User Guide, "Logging Amazon S3 API calls by using AWS CloudTrail," Section: "Data events." This document explains how CloudTrail captures S3 object-level API activity.

2. AWS CloudTrail User Guide, "Working with CloudTrail log files," Section: "CloudTrail userIdentity element." This section details the userIdentity field which contains the necessary user information.

3. Amazon CloudWatch User Guide, "Creating alarms from CloudTrail events using the console," Section: "Create a CloudWatch alarm for a CloudTrail event." This guide shows how to create alarms based on specific API activity captured by CloudTrail.