Example - Nested Stacks

This example takes the completed nested stacks example from cfn101 workshop and exports it as modules to Terraform.

Demonstrates the following

• That each AWS::CloudFormation::Stack in the root stack is exported to a Terraform module.
• That the module blocks for the exported modules are correctly linked up with refrences to input variables and other module outputs.

Inputs

The following CloudFormation templates form the nested stack:

• Root Stack
• VPC Stack
• EC2 Stack
• IAM Stack

The stacks were deployed with a root stack name of cfn-workshop-nested-stack.

Import run

This is the command to export cfn-workshop-nested-stack to Terraform in action...

A few points to note about the warnings here

• References to unsupported AWS pseudo parameters.
• The fact that the instance in EC2Stack contains AWS::CloudFormation::Init and user data.
• As a result of the above, the instance is scheduled for replacement.

This goes to show that importing a running EC2 instance to Terraform is not always possible, especially if that instance depends on CloudFormation init events, which don't happen in Terraform. Ultimately a new instance would need to be created using either remote provisioning or some other setup mechanism and the workload migrated to it.

Generated Outputs

A directory structure is generated in the workspace as follows

├ main.tf
├ module_imports.tf
├ terraform.tfvars
└ modules
  ├ cfn-workshop-nested-stack-EC2Stack-KGXCZCF8MN3C
  │  ├ main.tf
  │  └ terraform.tfvars
  ├ cfn-workshop-nested-stack-VpcStack-CEYRYZJTGP7X
  │  ├ main.tf
  │  └ terraform.tfvars
  └ cfn-workshop-nested-stack-IamStack-R7URHPP7NDAS
     └ main.tf