Question

Difficulty: HardBilling, Cost Management, and Resource Sharing Strategy

An enterprise-scale organization has structured its AWS multi-account environment with a management account, a core infrastructure account, and multiple Developer and Production member accounts under corresponding Organizational Units (OUs). The Solutions Architect is tasked with implementing a resource sharing, billing optimization, and security audit logging design under the following conditions:
1. Network subnets from the core infrastructure account must be shared with the Production OU to enable decentralized resource deployment, while preventing any resource sharing with external AWS accounts.
2. The organization has purchased a $100/hour Compute Savings Plan at the management account level. To keep development costs representative of standard rates, this Savings Plan's discount must not be applied to any accounts under the Developer OU.
3. AWS CloudTrail logs from all accounts must be stored in a central Amazon S3 bucket within a dedicated Security account. The logs must be encrypted at rest using a key that supports auditing and cross-account policy management.

Which two actions should the Solutions Architect take to meet these requirements? (Select TWO.)

  1. Enable resource sharing within AWS Organizations in AWS Resource Access Manager (RAM). In the core infrastructure account, create a resource share for the subnets and share them with the Production OU. In the Management account's Billing Preferences, disable Savings Plans discount sharing for the member accounts under the Developer OU.Answer
  2. In the Security account, create an Amazon S3 bucket encrypted by default with an AWS KMS Customer Managed Key (CMK). Configure the S3 bucket policy to permit the s3:PutObject action from the AWS Organization ID, and modify the CMK key policy to allow the CloudTrail service principal to perform kms:GenerateDataKey* operations.Answer
  3. C
    Enable resource sharing within AWS Organizations in AWS RAM. In the core infrastructure account, create a resource share for the subnets and share them with the Production OU. Apply a Service Control Policy (SCP) to the Developer OU that contains a deny statement for the savingsplans:ApplySavingsPlan action.
  4. D
    In the Security account, create an Amazon S3 bucket encrypted by default with the AWS-managed KMS key (aws/s3). Configure the S3 bucket policy to permit the s3:PutObject action from the AWS Organization ID, and require secure transport (HTTPS) for all write requests.
  5. E
    Enable resource sharing with external entities in AWS RAM. In the core infrastructure account, create a resource share for the subnets and share them individually with the account IDs in the Production OU. In the Management account, create an AWS Billing Conductor billing group for the Developer OU and assign a custom pricing rule that excludes Savings Plans.

Answer

Enable resource sharing within AWS Organizations, share subnets with the Production OU using AWS RAM, and disable Savings Plans discount sharing for Developer OU accounts in Billing Preferences. Concurrently, in the Security account, create an S3 bucket with default encryption using a Customer Managed Key (CMK), configure the S3 bucket policy to allow s3:PutObject for the AWS Organization, and configure the KMS key policy to grant key usage to the CloudTrail service principal.
The correct actions involve configuring AWS RAM to share VPC subnets internally within AWS Organizations, disabling Savings Plans discount sharing for Developer OU member accounts in the Billing Preferences of the management account, and utilizing a Customer Managed Key (CMK) with a permissive key policy for secure cross-account CloudTrail log encryption in a central S3 bucket.

Step-by-Step Solution

1
Configure VPC subnet sharing using AWS Resource Access Manager (RAM).
Subnets are shared from the Central Infrastructure account with the Production OU without enabling external sharing.
This satisfies the requirement to share subnets centrally and securely within the Organization.
2
Restrict Savings Plans application to the Production accounts.
Savings Plans discount sharing is disabled for the accounts under the Developer OU in the Management account's Billing Preferences.
This prevents the Compute Savings Plan from applying to Developer accounts, preserving their normal pricing structure for accurate budget tracking.
3
Configure centralized S3 logging with cross-account KMS encryption.
An S3 bucket is created in the Security account using a Customer Managed Key (CMK) for default encryption. The S3 bucket policy allows s3:PutObject from the Organization, and the KMS key policy grants kms:GenerateDataKey* to the CloudTrail service principal.
This enables secure, encrypted cross-account log delivery. AWS managed keys (aws/s3) cannot be used because their policies cannot be customized to allow cross-account operations.

Key Concept

Multi-account resource sharing, billing isolation preferences, and cross-account KMS encryption keys within an AWS Organization.
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