How to get the latest lambda version in cloudformation yml?

Question

I'm trying to reference an edge lambda for cloudfront distribution in cloudformation.

What I have now is:

          LambdaFunctionARN:
            Fn::GetAtt: [BasicAuthLambdaFunction,Arn]

But I get this error:

An error occurred: GGGCloudFrontDistribution - The function ARN must reference a specific function version. (The ARN must end with the version number.)

So.. is there some kind of technique to reference the latest version of the function?

Answer 1

You can't use the latest version. You have to use a specific version as the documentation you linked states:

You must specify the ARN of a function version; you can't specify a Lambda alias or $LATEST.

If you are creating the Lambda function in your template, you can also create a version and use that.

  BasicAuthLambdaFunctionVersion: 
    Type: "AWS::Lambda::Version"
    Properties:
      FunctionName:
        Ref: BasicAuthLambdaFunction
# ...
      LambdaFunctionARN:
        Fn::GetAtt: [BasicAuthLambdaFunctionVersion,Arn]

Note that when updating the stack, a new version will not be created when the Lambda function code changes. You have to manually create and use a new version by changing the name of BasicAuthLambdaFunctionVersion to BasicAuthLambdaFunctionVersion2 or something else. To automate this, you can edit the template with a script before using it.

If you are using the Serverless Framework, take a look at:

https://github.com/silvermine/serverless-plugin-cloudfront-lambda-edge https://github.com/serverless/serverless/issues/3944