Aws-sam-cli: Python Lambda Dependencies not built when defined in nested template

[alastairmccormack]

Description:

When a Python Lambda is defined within a Nested Stack and referenced from template.yaml, sam build fails to build dependecies defined in requirements.txt

This means that Lambdas fail to execute due to missing dependecies.

Steps to reproduce the issue:

1. datasource.yaml:

    AWSTemplateFormatVersion: '2010-09-09'
    Transform: AWS::Serverless-2016-10-31

    Globals:
        Function:
            Timeout: 3

    Parameters:
      ResolverNameParam:
        Type: String

      ApiIdParam:
        Type: String

      LambdaHandlerMethodParam:
        Type: String

    Resources:
      LambdaResolverFunction:
          Type: AWS::Serverless::Function
          Properties:
              CodeUri: src
              Handler: myhandler
              Runtime: python3.7
              Tracing: Active

1. template.yaml:

   AWSTemplateFormatVersion: '2010-09-09'
   Transform: AWS::Serverless-2016-10-31
   
   Globals:
       Function:
           Timeout: 3
   
   Resources:
   
       MyLambda:
         Type: AWS::CloudFormation::Stack
         Properties:
           TemplateURL: lambda.yaml
   

2. src/requirements.txt

   requests
   

3. src/test.py

   def myhandler(event, context):
     print(event)
   

4. sam build

   Build Succeeded
   
   Built Artifacts  : .aws-sam/build
   Built Template   : .aws-sam/build/template.yaml
   
   Commands you can use next
   =========================
   [*] Invoke Function: sam local invoke
   [*] Package: sam package --s3-bucket <yourbucket>
   

5. sam package --output-template-file packaged.yaml --s3-bucket mybucket

   Successfully packaged artifacts and wrote output template to file packaged.yaml.
   Execute the following com....
   

Observed result:

1. aws s3 cp --recursive s3://mybucket/ .
2. unzip 2b35401382a3a5ded0df8b7849ba2f99

3. ls

   requirements.txt
   test.py
   

Expected result:

1. ls

   requests
   requirements.txt
   test.py
   

[keetonian]

Moving to the SAM CLI repo for help with sam build

[jfuss]

@use-sparingly The template.yaml file does not have any functions within it. SAM CLI does not traverse Nested Stacks. You will need to build the template that contains the functions. So in your case you will need to run sam build -t lambda.yaml to build the functions within that template.

Closing as we don't yet support Nested Templates in SAM build or any other commands except package. We should create a general issue for this support.