AWS CloudFormation - using !Ref inside !Sub - json

Question

I'm writing AWS CloudFormation template (using yaml) which creates AWS Service Catalog Product.
I'm getting the template for the product using parameter S3FilePath which has a value like the above path: https://bucket.s3-eu-west-1.amazonaws.com/template.yml.
The URL to the file needs to be send in a JSON format as shown here (this example works):
Resources:
Type: AWS::ServiceCatalog::CloudFormationProduct
Properties:
Description: Example Product
Distributor: xyz
Name: ExampleProduct
Owner: xyz
ProvisioningArtifactParameters:
- Description: Example Product
Info: { "LoadTemplateFromURL": "https://bucket.s3-eu-west-1.amazonaws.com/template.yml" }
Name: Version1
I tried to replace the URL using !Sub and !Ref as shown below:
Parameters:
S3FilePath:
Type: String
Description: file name
Resources:
Type: AWS::ServiceCatalog::CloudFormationProduct
Properties:
Description: Example Product
Distributor: xyz
Name: ExampleProduct
Owner: xyz
ProvisioningArtifactParameters:
- Description: Example Product
Info: !Sub
- '{ "LoadTemplateFromURL": "${FILEPATH}" }'
- {FILEPATH: !Ref S3FilePath}
Name: Version1
But the CloudFormation stack fails with the error: "invalid input".
I guess I am building the JSON in a wrong way, I tried to use \ before each ' " ' but it didn't help either and I couldn't find an example which explain how to build this correctly. There is no problem with the S3FilePath parameter.
Can you please advice how to use the !Sub and !Ref correctly to build the JSON? Thanks.

Answer 1

Here is an example: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-sub.html#w2ab1c25c28c59c11
Despite the documentation saying the Info parameter is JSON, the example shows just a name/value pair (Map): https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-servicecatalog-cloudformationproduct-provisioningartifactproperties.html
Try formatting your string as
Info: !Sub
- "LoadTemplateFromURL": "${FILEPATH}"
- {FILEPATH: !Ref S3FilePath}

Answer 2

You can reference any Parameters or LogicalResourceId directly inside a !Sub like so:
ProvisioningArtifactParameters:
- Description: Example Product
Info: !Sub '{ "LoadTemplateFromURL": "${S3FilePath}" }'
Name: Version1
This should work totally fine. The way you were doing substitutions is useful when you want to use conditions and/or mapping inside a !Sub.

Answer 3

I think it should be simply:
ProvisioningArtifactParameters:
- Description: Example Product
Info:
LoadTemplateFromURL: !Ref S3FilePath
Name: Version1
This is at least what I have in my own AWS::ServiceCatalog::CloudFormationProduct templates.
ProvisioningArtifactParameters:
- DisableTemplateValidation: false
Info:
LoadTemplateFromURL: !Ref S3FilePath