How to align unique stacks across an organization?

So i would approach this by splitting this problem into 2. I would suggest that managing stacks across multiple accounts within an Organization is best done using StackSets have you considered using them? This leaves you with the issue of having different parameters per account/region. Whilst StackSets does have some functional to override parameters per stack instance in my experience it can be a little "tricky" to get right and be sure the values are as expected. Therefore i would consider separating this problem out by using another technology to hold the parameter values SSM parameters for example and using a naming convention for them to mean that your StackSet parameters would be consistent.

It does depend on the numbers and the variation you have in your use case though, so it might not be a good fit for your use case specifically.

I hope this has helped a little none the less.

1. Create a Centralized CloudFormation Template

Single Template, Different Parameters: Design a CloudFormation template that is flexible and parameterized. The template should contain all the resources that are common across all stacks but allow for parameters that can vary by account.

Use Parameters for Customization: Define parameters within the template for aspects that need to be unique (e.g., VPC IDs, Subnet IDs, instance types, environment-specific configurations).

2. Store Parameters Separately

Parameter Store or Secrets Manager: Use AWS Systems Manager Parameter Store or AWS Secrets Manager to store parameters for each account. This allows you to centrally manage and retrieve parameters when deploying the stack.

Parameter Files: Alternatively, maintain parameter files (e.g., JSON or YAML) for each account/environment in a version-controlled repository (e.g., Git). Each file corresponds to an account and contains the unique parameters required by the template.

3. Use StackSets for Deployment

AWS CloudFormation StackSets: Utilize StackSets to deploy your CloudFormation template across multiple AWS accounts and regions. StackSets enable centralized management of stacks in multiple accounts and regions.

Customized Parameters per Stack Instance: When creating or updating a StackSet, you can specify different parameters for each stack instance, allowing each account to have its own unique configuration while using the same template.

4. Version Control and Automated Updates

Template in Version Control: Store your CloudFormation template in a version-controlled repository like Git. Use branches to manage different versions of the template.

Continuous Integration/Continuous Deployment (CI/CD): Set up a CI/CD pipeline (e.g., using AWS CodePipeline, Jenkins, or GitHub Actions) to automatically deploy updates to the template across all accounts using StackSets.

Automated Rollouts: When you need to update the template, trigger the pipeline to push the changes. The parameters will remain unchanged unless explicitly modified.

5. Managing Parameter Changes

Parameter Change Process: If parameters need to be changed (e.g., new environment variables or resource IDs), update the corresponding parameter store entry or parameter file. The StackSet can be configured to only update stacks where the parameters have changed.

Notifications and Monitoring: Set up notifications (e.g., via Amazon SNS) to alert relevant teams of parameter changes or stack updates. Use Amazon CloudWatch to monitor stack statuses and catch any issues during deployment.

6. Testing and Staging

Testing Changes: Before rolling out changes to all accounts, test updates in a staging environment. This ensures that the template works as expected with different parameter sets.

Staging Environment: Maintain a staging account where changes can be tested against a parameter set similar to what’s used in production.

7. Documenting the Process

Documentation: Document the process for managing and updating stacks across accounts, including where parameters are stored, how updates are rolled out, and who is responsible for different parts of the stack management process.

Training: Ensure that teams involved in managing the stacks are trained on the process and understand how to handle updates and parameter changes.

Example Workflow:

Central Template: Store your CloudFormation template in a Git repository.

Parameters: Store parameters per account in Systems Manager Parameter Store or as JSON/YAML files in the same Git repository.

**StackSets: **Deploy the template using StackSets, specifying the appropriate parameters for each account.

**CI/CD Pipeline: **Trigger automated deployments when the template is updated, ensuring consistent rollouts across all accounts.

Monitor and Document: Keep track of stack statuses and maintain clear documentation.

Advantages of This Approach:

Consistency: Ensures all stacks across the organization are consistent with the same template.

Flexibility: Allows for account-specific customizations via parameters.

Scalability: Easily scales to support multiple accounts and regions.

Centralized Management: Facilitates centralized updates while allowing for decentralized parameter management.