AWS CloudFormation - Creating Layer Version and Function that uses layer

Question

I have a Cloudformation template that currently looks roughly like the following.

Resources: MyLayer: Type: AWS::Lambda::LayerVersion Properties: CompatibleRuntimes: - nodejs12.x - nodejs10.x Content: ../layers/nodejs/ LayerName: myLayer ### etc... MyLambda: Type: AWS::Lambda::Function DependsOn: MyLayer Properties: Code: lambdas/my-lambda.js Description: A lambda that makes use of MyLayer FunctionName: myLambda Handler: my-lambda.handler Layers: !Ref CommonLayer ### etc... 

The core idea here is I want to create a new LayerVersion and have the Lambda update to this latest LayerVersion on every deployment. I am having trouble inserting MyLayer's Arn into MyLambda's Layer property. Here is what I have tried:

1. !Ref CommonLayer which I saw returns the Arn based on this CloudFormation Cheatsheet. I get a failure when creating the stack at the creation of MyLambda (output shows MyLayer has been successfully created) saying: "Value of property Layers must be of type List of String"

2. !GetAtt CommonLayer.Arn however this function is just not supported for Layers/ the return value does not have an Arn field.

Is this a YAML syntax type problem or is my goal of creating a Layer and then a Lambda that depends on said Layer not possible in one Cloudformation template? Thanks!

Answer 1

Value of property Layers must be of type List of String

Layers must be a List. You’ll have to replace:

 MyLambda: Properties: Layers: !Ref CommonLayer 

With this:

 MyLambda: Properties: Layers: - !Ref CommonLayer 

Hope that helps :)