Provide passthrough `Code` property for `AWS::Serverless::Function`.

[garretwilson]

SAM's AWS::Serverless::Function removes the ability to use imported values in referring to the bucket and filename of my uploaded ZIP file for AWS Lambda. This is an inherent issue with the SAM transform design; see e.g. aws/serverless-application-model#2533 and a long comment in another ticket explaining all the gory details.

As explained in detail in aws/serverless-application-model#3264, I can do the following just fine using AWS::Lambda::Function, which uses Code instead of CodeUri. It looks like this:

      Code:
        S3Bucket:
          Fn::ImportValue:
            !Sub "other-stack-${env}:stagingBucket"
        S3Key: !Sub "foo-${ver}-aws-lambda.zip"

But I can't do that with AWS::Serverless::Function:

      CodeUri: !Sub
        - "s3://${bucket}/foo-${ver}-aws-lambda.zip"
        - bucket: my-staging-bucket
            Fn::ImportValue:
              !Sub "other-stack-${env}:stagingBucket"

That produces:

Error: Failed to create changeset for the stack: my-stack, ex: Waiter ChangeSetCreateComplete failed: Waiter encountered a terminal failure state: For expression "Status" we matched expected path: "FAILED" Status: FAILED. Reason: Transform AWS::Serverless-2016-10-31 failed with: Invalid Serverless Application Specification document. Number of errors found: 1. Resource with id [MyFunction] is invalid. 'CodeUri' requires Bucket and Key properties to be specified.

Please add a Code pass-through property to AWS::Serverless::Function so we can at least work around this shortcoming in the design of SAM.

[GavinZZ]

Hi thanks for creating a issue. I apologize for the trouble you've been through. I'll bring it up for discussion with the team and get back to you soon.

[GavinZZ]

Hi @garretwilson, I've brought this up to the team and we're having discussion on potential workaround/solution. Meanwhile I just want to quickly confirm that you've also tried with the following syntax and it doesn't work for you.

  CodeUri:
    Bucket:
      Fn::ImportValue:
        !Sub "other-stack-${env}:stagingBucket"
    Key: !Sub "foo-${ver}-aws-lambda.zip"

[garretwilson]

Well I'd like to answer your question, but suddenly SAM is doing all sorts of crazy things, as I just reported in aws/aws-sam-cli#6014. (Sigh. If it's not one thing, it's another thing breaking.)

[garretwilson]

@GavinZZ , I have wonderful news! (Note that the SAM traceback in aws/aws-sam-cli#6014 is still happening, but it doesn't seem to impede the actual deployment.) The format you asked about worked:

  CodeUri:
    Bucket:
      Fn::ImportValue:
        !Sub "other-stack-${env}:stagingBucket"
    Key: !Sub "foo-${ver}-aws-lambda.zip"

It seems that CodeUri allows not only a String but also a FunctionCode object, the latter of which has a Bucket and a Key. These seems to be passthrough properties for CloudFormation S3Bucket and S3Key. Yay! 🎉 Just what I need.

I wonder why nobody mentioned this during the long discussion in aws/serverless-application-model#3264? 🤔

Is the CodeUri > FunctionCode type new for SAM, or has it always been there?

[GavinZZ]

Great to hear that and hopefully this syntax will unblock you. 🎉🎉🎉

CodeUri supported both String syntax and FunctionCode object syntax and it's always been this way.

[GavinZZ]

Going to mark this issue as resolved. Feel free to re-open if you have any additional questions.

[garretwilson]

'CodeUri' supported both 'String' syntax and 'FunctionCode' object syntax and it's always been this way.

In that case, feel free to close this current ticket as "invalid", because SAM already has exactly what I was requesting!

Note also that aws/serverless-application-model#3264 therefore doesn't impact me, since I can always use the passthrough properties.

I'm so happy to find this out. Thanks for taking the time to suggest that.