Modify the template

Making our template multi-region

There are multiple potential strategies to deal with resources that require the content in S3 to be in the same region as the stack. In this example we will add a resource to the stack that copies the Lambda zip from the bucket in us-east-1 to the stack region before creating the lambda.

• In VSCode, edit the cfn_project/templates/lab3.template.yaml file. We’ll be adding the following snippet to the Resources section of the template.

  CopyZipsTemplate:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: !Sub "https://${S3BucketName}.s3.amazonaws.com/${S3KeyPrefix}templates/copy-zips.template.yaml"
      Parameters:
        S3BucketName: !Ref S3BucketName
        S3KeyPrefix: !Ref S3KeyPrefix
        SourceObjects: "lambda_functions/packages/GenRandom/lambda.zip"

This child stack contains a Lambda backed custom resource that takes the SourceObjects passed in and copies it to a new bucket in the same region as the stack. The outputs return the name of the new bucket, that we will use in the Code property of our GenRandomLambda resource.

    GenRandomLambda:
      Type: AWS::Lambda::Function
      Properties:
        Description: Lambda creates simple random string
        Handler: lambda_function.handler
        Runtime: python3.7
        Role: !GetAtt 'LambdaExecutionRole.Arn'
        Timeout: 300
        Code:
          S3Bucket: !GetAtt 'CopyZipsTemplate.Outputs.LambdaZipsBucket'
          S3Key: !Sub '${S3KeyPrefix}lambda_functions/packages/GenRandom/lambda.zip'

The full cfn_project/templates/lab3.template.yaml template should reflect the following:

• Feel free to copy and paste!

  AWSTemplateFormatVersion: 2010-09-09
  Parameters:
    S3BucketName:
      AllowedPattern: '^[0-9a-zA-Z]+([0-9a-zA-Z-]*[0-9a-zA-Z])*$'
      ConstraintDescription: >-
        Bucket name can include numbers, lowercase letters, uppercase
        letters, and hyphens (-). It cannot start or end with a hyphen (-).
      Description: >-
        S3 bucket name for assets. Bucket name can
        include numbers, lowercase letters, uppercase letters, and hyphens (-). It
        cannot start or end with a hyphen (-).
      Type: String
    S3KeyPrefix:
      AllowedPattern: '^[0-9a-zA-Z-/]*$'
      ConstraintDescription: >-
        Can include numbers, lowercase letters, uppercase letters, hyphens (-), and forward slash (/).
      Default: 'cfn-project/'
      Description: >-
        S3 key prefix where assets are located should end with forward slash (/).
      Type: String
  Resources:
    LambdaExecutionRole:
      Type: AWS::IAM::Role
      Properties:
        AssumeRolePolicyDocument:
          Version: '2012-10-17'
          Statement:
          - Effect: Allow
            Principal:
              Service:
              - lambda.amazonaws.com
            Action:
            - sts:AssumeRole
        Path: "/"
        Policies:
        - PolicyName: root
          PolicyDocument:
            Version: '2012-10-17'
            Statement:
            - Effect: Allow
              Action:
              - logs:*
              Resource: arn:aws:logs:*:*:*
    GenRandomLambda:
      Type: AWS::Lambda::Function
      Properties:
        Description: Lambda creates simple random string
        Handler: lambda_function.handler
        Runtime: python3.7
        Role: !GetAtt 'LambdaExecutionRole.Arn'
        Timeout: 300
        Code:
          S3Bucket: !GetAtt 'CopyZipsTemplate.Outputs.LambdaZipsBucket'
          S3Key: !Sub '${S3KeyPrefix}lambda_functions/packages/GenRandom/lambda.zip'
    StringGenerator:
      Type: Custom::RandomString
      Properties:
        ServiceToken: !GetAtt GenRandomLambda.Arn
        Length: 12
    CopyZipsTemplate:
      Type: AWS::CloudFormation::Stack
      Properties:
        TemplateURL: !Sub "https://${S3BucketName}.s3.amazonaws.com/${S3KeyPrefix}templates/copy-zips.template.yaml"
        Parameters:
          S3BucketName: !Ref S3BucketName
          S3KeyPrefix: !Ref S3KeyPrefix
          SourceObjects: "lambda_functions/packages/GenRandom/lambda.zip"
  Outputs:
    GeneratedRandomString:
      Description: Generated Random String
      Value: !GetAtt StringGenerator.RandomString