Cloudformation Lessons learned:
================================

* Can't update a stack that's in ROLLBACK_COMPLETE.  must delete it first.

* URL for resource types: 
  https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-template-resource-type-ref.html

* Deleted stacks stay in 'delete_complete' state for 90 days.

* Potential way to avoid having to mess w/ami names:
  https://xebia.com/blog/keeping-your-amis-up-to-date-in-aws-cloudformation/

* To use 'latest image' in CF templates:
  * Create a SSM parameter store
  * Use the /aws public parameters to find latest.
  * Should use /aws/service/ami-amazon-linux-latest/amzn-ami-hvm-x86_64-ebs
  * In parameters section, add something for imageid::

      ImageId:
        Type: AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>
        Default: /aws/service/ami-amazon-linux-latest/al2023-ami-kernel-6.1-x86_64

* Region is defined as a cli parameter, not an attribute for resources::

    aws cloudformation deploy --region us-east-2 --template-file ...

* To deploy, use template-file, to update, use template-body.  Consistency is a
  wonderful thing::

    aws cloudformation deploy --region us-east-2 --template-file ...
    VS
    aws cloudformation update-stack --template-body file://...
  
* Can't use external scripts to identify parameters such as myip like we can
  in terraform.