LatestLayerVersion AWS CloudFormation macro

This AWS CloudFormation lambda-powered macro is invoked by CloudFormation when deploying your templates. It returns the ARN of the latest AWS LayerVersion available, based on a LayerVersion name or LayerVersion ARN.

Getting Started

Example of use

You can invoke the LatestLayerVersion macro using Fn::Transform, as follows:

MyLambdaFunction:
  Type: AWS::Serverless::Function
  Properties:
    FunctionName: MyLambdaFunction
    ...
    Layers:
      - Fn::Transform:
          Name: LatestLayerVersion
          Parameters:
            LayerName: MyLambdaLayer
    MemorySize: 128
    Timeout: 300

Assuming that MyLambdaLayer has 5 versions, as it is deployed, your CloudFormation template will be templated as follows:

MyLambdaFunction:
  Type: AWS::Serverless::Function
  Properties:
    FunctionName: MyLambdaFunction
    ...
    Layers:
      - arn:aws:lambda:<aws_region>:<aws_account_id>:layer:MyLambdaLayer:5
    MemorySize: 128
    Timeout: 300

Macro parameters

When using Fn::Transform, you can/must pass any of the following parameters:

Parameter name	Type	Required	Description
LayerName	String or List (will be concatenated)	True	The name or Amazon Resource Name (ARN) of the layer. It can be any for the following formats: - Name: MyLambdaLayer - ARN: arn:aws:lambda:us-west-2:111122223333:layer/MyLambdaLayer - LayerVersionARN: arn:aws:lambda:us-west-2:111122223333:layer/MyLambdaLayer:1
CompatibleRuntime	String or List (will be concatenated)	False	A runtime identifier. For example, go1.x.

Installation

Software prerequisites

• AWS CLI (1.17.14+);
• Python (3.8.2+);
  • boto3 (1.16.8+);
• SAM CLI (0.47.0+).

CloudFormation configuration

Required capabilities

• CAPABILITY_NAMED_IAM: This stack template(s) include resources that affect permissions in your AWS account (e.g. creating new AWS Identity and IAM users). You must explicitly acknowledge this by specifying this capability.

Template parameters

Parameter name	Type	Default	AllowedValues	Description
MacroName	String	LatestLayerVersion		The name of the macro. The name of the macro must be unique across all macros in the account. This property is passed directly to the Name property of an AWS::CloudFormation::Macro resource.
KmsKeyArn	String	NONE	If set, must match a KMS Key ARN. Example: arn:aws:kms:us-west-2:111122223333:key/1234abcd-12ab-34cd-56ef-1234567890ab	If set, will be used to encrypt the AWS Lambda log group.

Deploying the application

This assumes your AWS CLI environment is properly configured.

• From the project root directory, run the AWS SAM CLI to build and deploy the Cloudformation application. It is recommended to use the --guided option in order to configure the application deployment, including template parameters:

  sam build
  sam deploy --guided --capabilities "CAPABILITY_NAMED_IAM"

• You will be prompt with a selection menu, generating a configuration recap as follows:

  Deploying with following values
  ===============================
  Stack name                   : macro-layer-latest-version
  Region                       : eu-west-1
  Confirm changeset            : True
  Deployment s3 bucket         : <your_cfn_deployment_bucket>
  Capabilities                 : ["CAPABILITY_NAMED_IAM"]
  Parameter overrides          : {"MacroName": "LatestLayerVersion", "KmsKeyArn": "NONE"}
  Signing Profiles             : {}

• Deploy the application to your AWS account by confirming the Cloudformation changeset.