AWS Certified Solutions Architect – Professional — Question 704

A company has an organization that has many AWS accounts in AWS Organizations. A solutions architect must improve how the company manages common security group rules for the AWS accounts in the organization.
The company has a common set of IP CIDR ranges in an allow list in each AWS account to allow access to and from the company's on-premises network.
Developers within each account are responsible for adding new IP CIDR ranges to their security groups. The security team has its own AWS account. Currently, the security team notifies the owners of the other AWS accounts when changes are made to the allow list.
The solutions architect must design a solution that distributes the common set of CIDR ranges across all accounts.
Which solution meets these requirements with the LEAST amount of operational overhead?

Answer options

• A. Set up an Amazon Simple Notification Service (Amazon SNS) topic in the security team's AWS account. Deploy an AWS Lambda function in each AWS account. Configure the Lambda function to run every time an SNS topic receives a message. Configure the Lambda function to take an IP address as input and add it to a list of security groups in the account. Instruct the security team to distribute changes by publishing messages to its SNS topic.
• B. Create new customer-managed prefix lists in each AWS account within the organization. Populate the prefix lists in each account with all internal CIDR ranges. Notify the owner of each AWS account to allow the new customer-managed prefix list IDs in their accounts in their security groups. Instruct the security team to share updates with each AWS account owner.
• C. Create a new customer-managed prefix list in the security team's AWS account. Populate the customer-managed prefix list with all internal CIDR ranges. Share the customer-managed prefix list with the organization by using AWS Resource Access Manager. Notify the owner of each AWS account to allow the new customer-managed prefix list ID in their security groups.
• D. Create an IAM role in each account in the organization. Grant permissions to update security groups. Deploy an AWS Lambda function in the security team's AWS account. Configure the Lambda function to take a list of internal IP addresses as input, assume a role in each organization account, and add the list of IP addresses to the security groups in each account.

Correct answer: C

Explanation

Creating a customer-managed prefix list in a central account and sharing it via AWS Resource Access Manager (AWS RAM) allows for centralized administration of the IP CIDR ranges. When the security team updates the prefix list in their account, the changes are automatically applied to all security groups referencing that prefix list across the organization. Other options involving custom AWS Lambda functions or manual per-account updates introduce significantly more operational overhead and complexity.