About enrolling existing accounts - AWS Control Tower
What happens during account enrollmentEnroll existing accounts with VPCsEnroll accounts with AWS Config resources

About enrolling existing accounts

You can extend AWS Control Tower governance to an individual, existing AWS account when you enroll it into an organizational unit (OU) that's already governed by AWS Control Tower. Eligible accounts exist in unregistered OUs that are part of the same AWS Organizations organization as the AWS Control Tower OU.

Several methods exist for enrolling accounts into AWS Control Tower. The information on this page applies to all methods of enrollment.

Note

You cannot enroll an existing AWS account to serve as your audit or log archive account except during initial landing zone setup.

What happens during account enrollment

During the enrollment process, AWS Control Tower performs these actions:

  • Baselines the account, which includes deploying these stack sets:

    • AWSControlTowerBP-BASELINE-CLOUDTRAIL

    • AWSControlTowerBP-BASELINE-CLOUDWATCH

    • AWSControlTowerBP-BASELINE-CONFIG

    • AWSControlTowerBP-BASELINE-ROLES

    • AWSControlTowerBP-BASELINE-SERVICE-ROLES

    • AWSControlTowerBP-BASELINE-SERVICE-LINKED-ROLES

    • AWSControlTowerBP-VPC-ACCOUNT-FACTORY-V1

    It is a good idea to review the templates of these stack sets and make sure that they don’t conflict with your existing policies.

  • Identifies the account through AWS IAM Identity Center or AWS Organizations.

  • Places the account into the OU that you've specified. Be sure to apply all SCPs that are applied in the current OU, so that your security posture remains consistent.

  • Applies mandatory controls to the account by means of the SCPs that apply to the selected OU as a whole.

  • Enables AWS Config and configures it to record all resources in the account.

  • Adds the AWS Config rules that apply the AWS Control Tower detective controls to the account.

Accounts and organization-level CloudTrail trails

For landing zone versions 3.1 and greater, if you've selected the optional AWS CloudTrail integration in landing zone settings:

  • All member accounts in an OU are governed by the AWS CloudTrail trail for the OU, enrolled or not.

  • When you enroll an account into AWS Control Tower, your account is governed by the AWS CloudTrail trail for the new organization. If you have an existing deployment of a CloudTrail trail, you may see duplicate charges unless you delete the existing trail for the account before you enroll it in AWS Control Tower.

  • If you move an account into a registered OU—for example by means of the AWS Organizations console or APIs—you may wish to remove any remaining account-level trails for the account. If you have an existing deployment of a CloudTrail trail, you will incur duplicate CloudTrail charges.

If you update your landing zone and choose to opt out of organization-level trails, or if your landing zone is older than version 3.0, organization-level CloudTrail trails do not apply to your accounts.

Enroll existing accounts with VPCs

AWS Control Tower handles VPCs differently when you provision a new account in Account Factory than when you enroll an existing account.

  • When you create a new account, AWS Control Tower automatically removes the AWS default VPC and creates a new VPC for that account.

  • When you enroll an existing account, AWS Control Tower does not create a new VPC for that account.

  • When you enroll an existing account, AWS Control Tower does not remove any existing VPC or AWS default VPC associated with the account.

Tip

You can change the default behavior for new accounts by configuring Account Factory, so it does not set up a VPC by default for accounts in your organization under AWS Control Tower. For more information, see Create an Account in AWS Control Tower Without a VPC.

Enroll accounts with AWS Config resources

The account to be enrolled must not have existing AWS Config resources. See Enroll accounts that have existing AWS Config resources.

Here are some example AWS Config CLI commands you can use to determine the status of your existing account's AWS Config resources, such as the configuration recorder and delivery channel.

View commands:

  • aws configservice describe-delivery-channels

  • aws configservice describe-delivery-channel-status

  • aws configservice describe-configuration-recorders

The normal response is something like "name": "default"

Delete commands:

  • aws configservice stop-configuration-recorder --configuration-recorder-name NAME-FROM-DESCRIBE-OUTPUT

  • aws configservice delete-delivery-channel --delivery-channel-name NAME-FROM-DESCRIBE-OUTPUT

  • aws configservice delete-configuration-recorder --configuration-recorder-name NAME-FROM-DESCRIBE-OUTPUT

Example for adding the AWSControlTowerExecution role

The following YAML template may assist you in creating the required role in an account, so that it can be enrolled programmatically.

AWSTemplateFormatVersion: 2010-09-09
Description: Configure the AWSControlTowerExecution role to enable use of your
  account as a target account in AWS CloudFormation StackSets.
Parameters:
  AdministratorAccountId:
    Type: String
    Description: AWS Account Id of the administrator account (the account in which
      StackSets will be created).
    MaxLength: 12
    MinLength: 12
Resources:
  ExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: AWSControlTowerExecution
      AssumeRolePolicyDocument:
        Version: 2012-10-17		 	 	 
        Statement:
          - Effect: Allow
            Principal:
              AWS:
                - !Ref AdministratorAccountId
            Action:
              - sts:AssumeRole
      Path: /
      ManagedPolicyArns:
        - !Sub arn:${AWS::Partition}:iam::aws:policy/AdministratorAccess