Bug: Using a Ref in StageName is Not Working Properly - Template.yaml

[Jonathynlee]

Description:

In template.yaml, I am using a parameter reference for StageName. When I go to build and deploy my sam application, it is replaced with "Stage". If I pass the string in directly there are no issues.

Steps to reproduce:

create parameter

Parameters:
  Stage:   
    Type: String   
    Description: Stage Name
    Default: develop

use parameter in API Gateway creation

  ProfileAPIGateway:   
    Type: AWS::Serverless::Api   
    Properties:   
      GatewayResponses:   
        DEFAULT_4XX:   
          ResponseParameters:   
            Headers:   
              Access-Control-Allow-Origin: "'*'"   
      Name: !Ref ApisApi   
      StageName: !Ref Stage
...

Please note the "StageName: !Ref Stage"

Observed result:

The incorrect StageName is being used

Expected result:

Logical resource Ids should all have "develop" at the end, not "Stage"

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

{
"version": "1.105.0",
"system": {
"python": "3.11.4",
"os": "Windows-10-10.0.19045-SP0"
},
"additional_dependencies": {
"docker_engine": "Not available",
"aws_cdk": "Not available",
"terraform": "Not available"
},
"available_beta_feature_env_vars": [
"SAM_CLI_BETA_FEATURES",
"SAM_CLI_BETA_BUILD_PERFORMANCE",
"SAM_CLI_BETA_TERRAFORM_SUPPORT",
"SAM_CLI_BETA_RUST_CARGO_LAMBDA"
]
}

[lucashuy]

Thanks for reporting this issue. I can reproduce the behaviour you see with the stage name reference. This is due to how we treat and resolve intrinsics, and in this case SAM does not resolve the Ref instrinsic to the parameter for stage names:

serverless-application-model/samtranslator/model/eventsources/push.py

Lines 734 to 740 in e302b20

	if isinstance(permitted_stage, str):
	if not permitted_stage:
	raise InvalidResourceException(rest_api_id, "StageName cannot be empty.")
	stage_suffix = permitted_stage
	else:
	stage_suffix = "Stage"

(aggregate issue: #2533)

Let me transfer this to over to the SAM repo in case the folks there have anymore insight.

[moelasmar]

Thanks @Jonathynlee for raising this issue.
As mentioned in this issue SAM Transform does not support intrinsic functions. So to make sure that SAM handles the created resources as you expect, we recommend you to use the AWS::LanguageExtensions Transform, and add it before SAM Transform so SAM receives the template after got processed, and intrinsic function got replaced with the actual values.

You can update your template, and replace

Transform: AWS::Serverless-2016-10-31

with

Transform:
  - AWS::LanguageExtensions
  - AWS::Serverless-2016-10-31

[Jonathynlee]

@moelasmar
Amazing! Thank you!

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