Enroll an existing AWS account - AWS Control Tower

Enroll an existing AWS account

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.

Set Up Trusted Access First

Before you can enroll an existing AWS account into AWS Control Tower you must give permission for AWS Control Tower to manage, or govern, the account. Specifically, AWS Control Tower requires permission to establish trusted access between AWS CloudFormation and AWS Organizations on your behalf, so that AWS CloudFormation can deploy your stack automatically to the accounts in your selected organization.

To learn more about trusted access and AWS CloudFormation StackSets, see AWS CloudFormation StackSets and AWS Organizations. When trusted access is enabled, AWS CloudFormation can create, update, or delete stacks across multiple accounts and AWS Regions with a single operation. AWS Control Tower relies on this trust capability so it can apply roles and permissions to existing accounts before it moves them into a registered organizational unit and thereby brings them under governance.

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-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 Single Sign-On 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 guardrails to the account by means of the SCPs that apply to the selected OU as a whole.

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

Note

When you enroll the 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.

Enrolling 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.

Recommended: You can set up a two-step approach to account enrollment

  • First, use an AWS Config conformance pack to evaluate how your accounts may be affected by some AWS Control Tower guardrails. To determine how enrollment into AWS Control Tower may affect your accounts, see Extend AWS Control Tower governance using AWS Config conformance packs.

  • Next, you may wish to enroll the account. If the compliance results are satisfactory, the migration path is easier because you can enroll the account without unexpected consequences.

  • After you've done your evaluation, if you decide to set up an AWS Control Tower landing zone, you may need to remove the AWS Config delivery channel and configuration recorder that were created for your evaluation. Then you'll be able to set up AWS Control Tower successfully.

Note

The conformance pack also works in situations where the accounts are located in OUs registered by AWS Control Tower, but the workloads run within AWS Regions that don’t have AWS Control Tower support. You can use the conformance pack to manage resources in accounts that exist in Regions where AWS Control Tower is not deployed.

Prerequisites for Enrollment

These prerequisites are required before you can enroll an account in AWS Control Tower:

  1. We recommend that the account should not have an AWS Config configuration recorder or delivery channel. These may be deleted through the AWS CLI before you can enroll an account. Otherwise, see Enroll accounts that have existing AWS Config resources for instructions on how you can modify your existing resources.

  2. The account that you wish to enroll must exist in the same AWS Organizations organization as the AWS Control Tower management account. The account that exists can be enrolled only into the same organization as the AWS Control Tower management account, in an OU that already is registered with AWS Control Tower.

  3. Before you can enroll an existing account in AWS Control Tower, the account must have the following roles, permissions, and trust relationships in place. Otherwise, enrollment will fail.

    Role Name: AWSControlTowerExecution

    Role Permission: AdministratorAccess (AWS managed policy)

    Role Trust Relationship:

    { "Version": "2012-10-17", "Statement": [ { "Effect": "Allow", "Principal": { "AWS": "arn:aws:iam::Management Account ID:root" }, "Action": "sts:AssumeRole", "Condition": {} } ] }

To check other prerequisites for enrollment, see Getting Started with AWS Control Tower.

Note

When you enroll an account into AWS Control Tower, your account is governed by the AWS CloudTrail trail for the AWS Control Tower 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.

What if the account does not meet the prerequisites?

To fulfill the prerequisites for account enrollment, you can follow these preparatory steps to move an account into the same organization as AWS Control Tower.

Preparatory steps to bring an account into the same organization as AWS Control Tower

  1. Drop the account from its existing organization. (You must provide a separate payment method if you use this approach.)

  2. Invite the account into the AWS Control Tower organization.

  3. Accept the invitation. (The account shows up in the root of the organization.) This step moves the account into the same organization as AWS Control Tower. It establishes SCPs and consolidated billing.

  4. Now you must fulfill the remaining enrollment prerequisites:

    • Create the necessary role.

    • Clear out the default VPC. (This part is optional—AWS Control Tower does not change your existing default VPC.)

    • Delete the AWS Config configuration recorder or delivery channel through the CLI if one exists.

    • Any other prerequisites, as needed.

  5. Enroll the account into AWS Control Tower. This step brings the account into full AWS Control Tower governance.

Here are some example AWS Config CLI commands you can use to determine the status of your 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

Note

You can send the invitation for the new organization before the account drops out of the old organization. The invitation will be waiting when the account drops out of its existing organization.

Optional steps for deprovisioning an account so it can be enrolled, keeping its stack

  1. Optionally, to keep the applied CFN, delete the stack instance from the stack sets, making sure to choose Retain stacks for the instance.

  2. Terminate the account provisioned product in AWS Service Catalog Account Factory. (This step only removes the provisioned product from AWS Control Tower, it does not actually delete the account.)

  3. Optionally, set up the account with the necessary billing details, as required for any account that does not belong to an organization, then remove the account from the organization. You would do this so that the account does not count against the total in your AWS Organizations quota.

  4. Clean up the account, if resources remain, and close it, following account closure steps given in Unmanaging a Member Account.

  5. If you have a Suspended OU with defined guardrails, you can move the account there instead of doing Step 1.

Automated Enrollment of AWS Organizations Accounts

You can use the enrollment method described in a blog post called Enroll existing AWS accounts into AWS Control Tower to enroll your AWS Organizations accounts into AWS Control Tower with a programmatic process.