sam build fails when providing a function LayerArn with a reference to a SSM::Parameter CF param

Description

When running sam build on a template that includes a Serverless::Function resource that specifies a LayerArn property with a reference to a CF Parameter name that is of Type AWS::SSM::Parameter<string> with a default value of the name of the param in param store, sam build reports an invalid Arn.

Steps to reproduce

1. git clone https://github.com/ericallam/sam-build-ssm-parameter-layer-arn-issue.git
2. cd sam-build-ssm-parameter-layer-arn-issue
3. sam build --debug

Observed result

View debug output here

Expected result

sam build should resolve the actual value of the param in param store and use that to determine if the LayerArn is valid.

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: macOS Mojave
2. sam --version: 0.13.0

[chizou]

I get that using --parameter-overrides works, but it’s a really non-intuitive way to need to get sam build to work when we want to pass any AWS::SSM parameter types.

It may make sense for sam build to ignore some validation. To build, we don’t need this Ref resolved.

This is exactly how it should behave if the Ref is an AWS::SSM::* parameter. I would imagine a reasonable person wouldn’t expect the parameter value be resolved at build time. Or at the very least, if sam build detects this type of parameter, it should output some kind of warning about needing to use a --parameter-override to pass the validation.

Otherwise, one has to search Github issues to find this solution.

[obsequiouswoe]

For clarity for anyone else fighting this bug the following literally got me working:

sam build --parameter-overrides param1=arn:::::::1 param2=arn:::::::1