How AWS Control Tower Works

This section describes at a high level how AWS Control Tower works. Your landing zone is a well-architected multi-account environment for all of your AWS resources. You can use this environment to enforce compliance regulations on all of your AWS accounts.

Structure of an AWS Control Tower Landing Zone

The structure of a landing zone in AWS Control Tower is as follows:

• Root – The parent that contains all other OUs in your landing zone.

• Security OU – This OU contains the Log Archive and Audit accounts. These accounts often are referred to as shared accounts. You can choose customized names for these shared accounts when you launch your landing zone. However, they cannot be renamed later.

• Sandbox OU – The Sandbox OU is created when you launch your landing zone, if you enable it. This and other registered OUs contain the enrolled accounts that your users work with to perform their AWS workloads.

• AWS SSO directory – This directory houses your AWS SSO users. It defines the scope of permissions for each AWS SSO user.

• AWS SSO users – These are the identities that your users can assume to perform their AWS workloads in your landing zone.

What happens when you set up a landing zone

When you set up a landing zone, AWS Control Tower performs the following actions in your management account on your behalf:

• Creates two AWS Organizations organizational units (OUs): Security, and Sandbox (optional), contained within the organizational root structure.

• Creates two shared accounts in the Security OU: the Log Archive account and the Audit account.

• Creates a cloud-native directory in AWS SSO, with preconfigured groups and single sign-on access.

• Applies 20 mandatory, preventive guardrails to enforce policies.

• Applies two mandatory, detective guardrails to detect configuration violations.

• Preventive guardrails are not applied to the management account.

• Except for the management account, guardrails are applied to the organization as a whole.

Safely Managing Resources Within Your AWS Control Tower Landing Zone and Accounts

• When you create your landing zone, a number of AWS resources are created. To use AWS Control Tower, you must not modify or delete these AWS Control Tower managed resources outside of the supported methods described in this guide. Deleting or modifying these resources will cause your landing zone to enter an unknown state. For details, see Guidance for Creating and Modifying AWS Control Tower Resources

• When you enable guardrails with strongly recommended guidance, AWS Control Tower creates AWS resources that it manages in your accounts. Do not modify or delete resources created by AWS Control Tower. Doing so can result in the guardrails entering an unknown state. For more information, see Guardrail Reference.

What Are the Shared Accounts?

In AWS Control Tower, three shared accounts in your landing zone are provisioned automatically during setup: the management account, the log archive account, and the audit account.

What is the management account?

This is the account that you created specifically for your landing zone. This account is used for billing for everything in your landing zone. It's also used for Account Factory provisioning of accounts, as well as to manage OUs and guardrails.

Note

It is not recommended to run any type of production workloads from an AWS Control Tower management account. Create a separate AWS Control Tower account to run your workloads.

When you set up your landing zone, the following AWS resources are created within your management account.

AWS service	Resource type	Resource name
AWS Organizations	Accounts	audit log archive
AWS Organizations	OUs	Security Sandbox
AWS Organizations	Service Control Policies	aws-guardrails-*
AWS CloudFormation	Stacks	AWSControlTowerBP-BASELINE-CLOUDTRAIL-MASTER
AWS CloudFormation	StackSets	AWSControlTowerBP-BASELINE-CLOUDTRAIL AWSControlTowerBP-BASELINE-CLOUDWATCH AWSControlTowerBP-BASELINE-CONFIG AWSControlTowerBP-BASELINE-ROLES AWSControlTowerBP-BASELINE-SERVICE-ROLES AWSControlTowerBP-SECURITY-TOPICS AWSControlTowerGuardrailAWS-GR-AUDIT-BUCKET-PUBLIC-READ-PROHIBITED AWSControlTowerGuardrailAWS-GR-AUDIT-BUCKET-PUBLIC-WRITE-PROHIBITED AWSControlTowerLoggingResources AWSControlTowerSecurityResources
AWS Service Catalog	Product	AWS Control Tower Account Factory
AWS CloudTrail	Trail	aws-controltower-BaselineCloudTrail
Amazon CloudWatch	CloudWatch Logs	aws-controltower/CloudTrailLogs
AWS Identity and Access Management	Roles	AWSControlTowerAdmin AWSControlTowerStackSetRole AWSControlTowerCloudTrailRolePolicy
AWS Identity and Access Management	Policies	AWSControlTowerServiceRolePolicy AWSControlTowerAdminPolicy AWSControlTowerCloudTrailRolePolicy AWSControlTowerStackSetRolePolicy
AWS Single Sign-On	Directory groups	AWSAccountFactory AWSAuditAccountAdmins AWSControlTowerAdmins AWSLogArchiveAdmins AWSLogArchiveViewers AWSSecurityAuditors AWSSecurityAuditPowerUsers AWSServiceCatalogAdmins
AWS Single Sign-On	Permission Sets	AWSAdministratorAccess AWSPowerUserAccess AWSServiceCatalogAdminFullAccess AWSServiceCatalogEndUserAccess AWSReadOnlyAccess AWSOrganizationsFullAccess

What is the log archive account?

This account works as a repository for logs of API activities and resource configurations from all accounts in the landing zone.

When you set up your landing zone, the following AWS resources are created within your log archive account.

AWS service	Resource type	Resource Name
AWS CloudFormation	Stacks	StackSet-AWSControlTowerGuardrailAWS-GR-AUDIT-BUCKET-PUBLIC-READ-PROHIBITED- StackSet-AWSControlTowerGuardrailAWS-GR-AUDIT-BUCKET-PUBLIC-WRITE-PROHIBITED StackSet-AWSControlTowerBP-BASELINE-CLOUDWATCH- StackSet-AWSControlTowerBP-BASELINE-CONFIG- StackSet-AWSControlTowerBP-BASELINE-CLOUDTRAIL- StackSet-AWSControlTowerBP-BASELINE-SERVICE-ROLES- StackSet-AWSControlTowerBP-BASELINE-ROLES- StackSet-AWSControlTowerLoggingResources-
AWS Config	AWS Config Rules	AWSControlTower_AWS-GR_AUDIT_BUCKET_PUBLIC_READ_PROHIBITED AWSControlTower_AWS-GR_AUDIT_BUCKET_PUBLIC_WRITE_PROHIBIT
AWS CloudTrail	Trails	aws-controltower-BaselineCloudTrail
Amazon CloudWatch	CloudWatch Event Rules	aws-controltower-ConfigComplianceChangeEventRule
Amazon CloudWatch	CloudWatch Logs	aws-controltower/CloudTrailLogs /aws/lambda/aws-controltower-NotificationForwarder
AWS Identity and Access Management	Roles	aws-controltower-AdministratorExecutionRole aws-controltower-CloudWatchLogsRole aws-controltower-ConfigRecorderRole aws-controltower-ForwardSnsNotificationRole aws-controltower-ReadOnlyExecutionRole AWSControlTowerExecution
AWS Identity and Access Management	Policies	AWSControlTowerServiceRolePolicy
Amazon Simple Notification Service	Topics	aws-controltower-SecurityNotifications
AWS Lambda	Applications	StackSet-AWSControlTowerBP-BASELINE-CLOUDWATCH-*
AWS Lambda	Functions	aws-controltower-NotificationForwarder
Amazon Simple Storage Service	Buckets	aws-controltower-logs-* aws-controltower-s3-access-logs-*

What is the audit account?

The audit account is a restricted account that's designed to give your security and compliance teams read and write access to all accounts in your landing zone. From the audit account, you have programmatic access to review accounts, by means of a role that is granted to Lambda functions only. The audit account does not allow you to log in to other accounts manually. For more information about Lambda functions and roles, see Configure a Lambda function to assume a role from another AWS account.

When you set up your landing zone, the following AWS resources are created within your audit account.

AWS service	Resource type	Resource name
AWS CloudFormation	Stacks	StackSet-AWSControlTowerGuardrailAWS-GR-AUDIT-BUCKET-PUBLIC-READ-PROHIBITED- StackSet-AWSControlTowerGuardrailAWS-GR-AUDIT-BUCKET-PUBLIC-WRITE-PROHIBITED- StackSet-AWSControlTowerBP-BASELINE-CLOUDWATCH- StackSet-AWSControlTowerBP-BASELINE-CONFIG- StackSet-AWSControlTowerBP-BASELINE-CLOUDTRAIL- StackSet-AWSControlTowerBP-BASELINE-SERVICE-ROLES- StackSet-AWSControlTowerBP-SECURITY-TOPICS- StackSet-AWSControlTowerBP-BASELINE-ROLES- StackSet-AWSControlTowerSecurityResources-*
AWS Config	Aggregator	aws-controltower-GuardrailsComplianceAggregator
AWS Config	AWS Config Rules	AWSControlTower_AWS-GR_AUDIT_BUCKET_PUBLIC_READ_PROHIBITED AWSControlTower_AWS-GR_AUDIT_BUCKET_PUBLIC_WRITE_PROHIBITED
AWS CloudTrail	Trail	aws-controltower-BaselineCloudTrail
Amazon CloudWatch	CloudWatch Event Rules	aws-controltower-ConfigComplianceChangeEventRule
Amazon CloudWatch	CloudWatch Logs	aws-controltower/CloudTrailLogs /aws/lambda/aws-controltower-NotificationForwarder
AWS Identity and Access Management	Roles	aws-controltower-AdministratorExecutionRole aws-controltower-CloudWatchLogsRole aws-controltower-ConfigRecorderRole aws-controltower-ForwardSnsNotificationRole aws-controltower-ReadOnlyExecutionRole aws-controltower-AuditAdministratorRole aws-controltower-AuditReadOnlyRole AWSControlTowerExecution
AWS Identity and Access Management	Policies	AWSControlTowerServiceRolePolicy
Amazon Simple Notification Service	Topics	aws-controltower-AggregateSecurityNotifications aws-controltower-AllConfigNotifications aws-controltower-SecurityNotifications
AWS Lambda	Functions	aws-controltower-NotificationForwarder

How Guardrails Work

A guardrail is a high-level rule that provides ongoing governance for your overall AWS environment. Each guardrail enforces a single rule, and it's expressed in plain language. You can change the elective or strongly recommended guardrails that are in force, at any time, from the AWS Control Tower console. Mandatory guardrails are always applied, and they can't be changed.

Preventive guardrails prevent actions from occurring. For example, the elective guardrail called Disallow Changes to Bucket Policy for Amazon S3 Buckets (Previously called Disallow Policy Changes to Log Archive) prevents any IAM policy changes within the log archive shared account. Any attempt to perform a prevented action is denied and logged in CloudTrail. The resource is also logged in AWS Config.

Detective guardrails detect specific events when they occur and log the action in CloudTrail. For example, the strongly recommended guardrail called Enable encryption for EBS volumes attached to EC2 instances detects whether an unencrypted Amazon EBS volume is attached to an EC2 instance in your landing zone.

For those who are familiar with AWS: In AWS Control Tower preventive guardrails are implemented with Service Control Policies (SCPs). Detective guardrails are implemented with AWS Config rules.

Related Topics

• Guardrails in AWS Control Tower

• Detect and resolve drift in AWS Control Tower

How AWS Control Tower Works With StackSets

AWS Control Tower uses AWS CloudFormation StackSets to set up resources in your accounts. Each stack set has StackInstances that correspond to accounts, and to AWS Regions per account. AWS Control Tower deploys one stack set instance per account and Region.

AWS Control Tower applies updates to certain accounts and AWS Regions selectively, based on CloudFormation parameters. When updates are applied to some stack instances, other stack instances may be left in Outdated status. This behavior is expected and normal.

When a stack instance goes into Outdated status, it usually means that the stack corresponding to that stack instance is not aligned with the latest template in the stack set. The stack remains in the older template, so it might not include the latest resources or parameters. The stack is still completely usable.

Here's a quick summary of what behavior to expect, based on AWS CloudFormation parameters that are specified during an update:

If the stack set update includes changes to the template (that is, if the TemplateBody or TemplateURL properties are specified), or if the Parameters property is specified, AWS CloudFormation marks all stack instances with a status of Outdated prior to updating the stack instances in the specified accounts and AWS Regions. If the stack set update does not include changes to the template or parameters, AWS CloudFormation updates the stack instances in the specified accounts and Regions, while leaving all other stack instances with their existing stack instance status. To update all of the stack instances associated with a stack set, do not specify the Accounts or Regions properties.

For more information, see Update Your Stack Set in the AWS CloudFormation User Guide.