example.yml

Parameters:
  AmazonMachineImageName:
    Type: String
    Description: Include wildcard if substring. (e.g. 'RHEL-8*')
  BucketName:
    Type: String
    Description: S3 bucket hosting the get-latest-ami.yml nested template.
Resources:
  latestAmiTemplate:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: !Sub https://${BucketName}.s3.${AWS::URLSuffix}/get-latest-ami.yml
  # Invoked here, and can be invoked multiple times.
  latestAmi:
    DependsOn: latestAmiTemplate
    Type: Custom::latestAmi
    Properties:
      ServiceToken: !GetAtt latestAmiTemplate.Outputs.LambdaServiceToken
      Name: !Ref AmazonMachineImageName
# This value can be inputted to resources (e.g. AWS::EC2::Instance),
# Included as an output value for simplicity, and to not provision resources.
Outputs:
  amiId:
    Value: !Ref latestAmi