A company hosts an internal application on Amazon EC2 instances. All application data and requests route through an AWS Site-to-Site VPN connection between the on-premises network and AWS. The company must monitor the application for changes that allow network access outside of the corporate network. Any change that exposes the application externally must be restricted automatically.
Which solution meets these requirements in the MOST operationally efficient manner?

A. Create an AWS Lambda function that updates security groups that are associated with the elastic network interface to remove inbound rules with noncorporate CIDR ranges. Turn on VPC Flow Logs, and send the logs to Amazon CloudWatch Logs. Create an Amazon CloudWatch alarm that matches traffic from noncorporate CIDR ranges, and publish a message to an Amazon Simple Notification Service (Amazon SNS) topic with the Lambda function as a target.
B. Create a scheduled Amazon EventBridge (Amazon CloudWatch Events) rule that targets an AWS Systems Manager Automation document to check for public IP addresses on the EC2 instances. If public IP addresses are found on the EC2 instances, initiate another Systems Manager Automation document to terminate the instances.
C. Configure AWS Config and a custom rule to monitor whether a security group allows inbound requests from noncorporate CIDR ranges. Create an AWS Systems Manager Automation document to remove any noncorporate CIDR ranges from the application security groups.
D. Configure AWS Config and the managed rule for monitoring public IP associations with the EC2 instances by tag. Tag the EC2 instances with an identifier. Create an AWS Systems Manager Automation document to remove the public IP association from the EC2 instances.