CloudFormation Macro Example

consumeMacroCfn.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: [AWS::Serverless-2016-10-31, AddSSMParametersMacro]
Description: SAM template for consuming a CloudFormation Macro

Resources:
  ExampleWithEnvVarFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: example-with-env-var
      Handler: function.handler
      Environment:
        Variables:
          LAMBDA_VALUE: ExampleFunction
   
   ExampleWithoutEnvVarFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: example-without-env-var
      Handler: function.handler      
          

createMacroCfn.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: SAM template for creating a CloudFormation Macro

Resources:
 AddSSMParametersFunction:
    Type: AWS::Serverless::Function
    Properties:
      Description: CFN Macro function to automatically add action parameters based on the presence environment variables
      CodeUri: auto-add-ssm-parameter
      Handler: function.handler
      
  AddSSMParametersMacro:
    Type: AWS::CloudFormation::Macro
    Properties:
      Name: AddSSMParameters
      Description: Adds SSM Parameters for lambdas with the LAMBDA_VALUE env var
      FunctionName:
        Ref: AddSSMParametersFunction

function.js

exports.handler = async function(event, context) {
  const lambdas = [];
  const resourceKeys = Object.keys(resources);
  for (let i = 0; i < resourceKeys.length; i++) {
    const resource = resources[resourceKeys[i]];
    if (resource.Type === 'AWS::Serverless::Function' && resource.Properties.Environment.Variables.LAMBDA_VALUE) {
      lambdas.push({
        name: resourceKeys[i],
        details: resource
      });
    }
  }
  
  lambdas.forEach((lambda) => {
    event.fragment.Resources[`${lambda.name}Parameter`] = {
        Type: 'AWS::SSM::Parameter',
        Properties: {
          Name: `${lambda.name}Parameter`,
          Type: 'String',
          Value: lambda.Properties.Environment.Variables.LAMBDA_VALUE
        }
      };
  });
  
  return {
    requestId: event.requestId,
    status: 'success',
    fragment: event.fragment
  };
}