cloudformation question

Yes, there is a way to overcome the need to manually copy new SubnetIds each time you recreate your infrastructure. You can use CloudFormation's cross-stack references to extract and use the existing SubnetId in your EC2 template. Here's how you can approach this:

1. In your first template (the one creating VPCs, subnets, etc.), you need to export the SubnetId values you want to use later. You can do this using the Export property in the Outputs section of your template. For example:

Outputs:
  SubnetId:
    Description: ID of the subnet
    Value: !Ref YourSubnetResource
    Export:
      Name: MySubnetId

2. In your second template (the one creating EC2 instances), you can then import these exported values using the Fn::ImportValue function. You would use it like this in your EC2 instance resource:

Resources:
  MyEC2Instance:
    Type: AWS::EC2::Instance
    Properties:
      SubnetId: !ImportValue MySubnetId
      # other instance properties...

By using this approach, you create a dependency between your stacks. The EC2 stack will always use the current SubnetId from the VPC stack, even if you tear down and recreate the infrastructure.

This method allows you to maintain separation between your network infrastructure and your compute resources while still allowing them to reference each other. It also means you don't need to manually update SubnetIds in your EC2 template each time you recreate your VPC stack.

Remember that when using cross-stack references, you cannot delete the first stack (the one with the exports) until all the stacks that depend on it are deleted. This aligns well with your goal of tearing down all stacks after you're done with your lab.

This approach provides a more robust and maintainable solution for your CloudFormation templates, allowing you to easily recreate your entire infrastructure without manual intervention.
Sources
Working with CloudFormation templates - AWS CloudFormation
How CloudFormation works - AWS CloudFormation
AWS CloudFormation - Overview of Deployment Options on AWS