One of the architectural patterns for application migration is about managing AWS Service Catalog products in multiple AWS Accounts and AWS Regions. AWS Service Catalog is used to create, share organize and govern the curated IaC templates. Governance and distribution of Infrastructure is simplified and accelerated. AWS uses CloudFormation Templates to define a collection of AWS resources aka stacks required for a solution or a product. StackSets extend this functionality by enabling us to create, update or delete stacks across multiple accounts and AWS Regions with a single operation. 

If a CloudFormation template must be made available to other AWS accounts or organizational units, then the portfolio is typically shared. A portfolio is a container that includes one or more products.   

On the other hand, this architectural pattern is an alternative approach that is based on AWS CloudFormation StackSets. Instead of sharing portfolio, we use AWS StackSet constraints to set AWS regions and accounts where the resources can be deployed and used. This approach helps to provision the Service Catalog products in multiple accounts, OUs and AWS Regions, and managed from a central location which meets governance requirements. 

The benefits of this approach are the following:  

1. the product is provisioned and managed from a primary account, and not shared with other accounts. 

2. This approach provides a consolidated view of all provisioned products (stacks) that are based on a specific set of templates. 

3. The use of a primary account makes the configuration with AWS Service management Connector easier 

4. It is easier to query and use products from the AWS Service Catalog.  

The architecture involves an AWS management account and a target Organizational Unit (OU) account. The CloudFormation template and the service catalog product are in the management account.  The CloudFormation stack and its resources are in the target OU account. The user creates an AWS CloudFormation template to provision AWS resources, in JSON or Yaml format. The CloudFormation template creates a product in AWS Service Catalog, which is added to a portfolio. The user creates a provisioned product, which creates CloudFormation stacks in the target accounts. Each stack provisions the resources specified in the CloudFormation templates. 

The steps to provision products across accounts include: 1. Creating a portfolio say with the AWS command line interface 2. Create the template that describes the resources, 3. Create a product with version title and description and 4. Apply constraints to the portfolio to configure product deployment options such as multiple AWS accounts, regions and permissions and 5. Provide permissions to users so that they can launch the products in the portfolio.