CfnResource Data retrieval breaks when used from Python CDK but not when used from CloudFormation

[suttonsp0]

This issue has got me scratching my head. It started when I built a custom resource and put the data I'm looking for into the helper like so:

helper.Data["FileServerIp"] = file_server_ip

I accessed the data in the python cdk app like so:

CfnOutput(
     self,
     "FileServerIpOutput",
     value=fsx_file_server_ip_retrieval.get_att_string("FileServerIp")
)

This resulted in this error:

CustomResource attribute error: Vendor response doesn't contain FileSystemId attribute in object

I confirmed in the logs that it is returning the ip address correctly:

[DEBUG]	2024-11-26T22:21:56.075Z	0fa30484-a10c-4f34-bc30-089ba0698aed	
{
    "Status": "SUCCESS",
    "PhysicalResourceId": "FileServerIpRetrieval-fs-06c2bba33ed9f31da",
    "StackId": "arn:aws:cloudformation:us-east-2:redacted:stack/test6/ba055540-ac44-11ef-bfcf-064a3121c883",
    "RequestId": "0eeb6ee4-e11a-4e16-bf14-3caf8bc65190",
    "LogicalResourceId": "FsxInstructionGenerationLambdaConstructFsxFileServerIpRetrievalD63DD733",
    "Reason": "",
    "Data": {
        "FileServerIp": "10.0.42.3"
    },
    "NoEcho": false
}

The weird part is that I configured the lambda to not tear down on failure and then I re-used it from a CloudFormation template like this:

AWSTemplateFormatVersion: "2010-09-09"
Resources:
  MyTest:
    Type: "Custom::MyTest"
    Properties:
      ServiceToken: "arn:aws:lambda:us-east-2:redacted:function:test-9-FsxFileServerIPRetrievalLambdaF104C778-on3uRRR1cQQt"
      FileSystemId: "my-file-system-id"
Outputs:
  FileSystemId:
    Value: !GetAtt MyTest.FileServerIp

And it worked. I don't know why it would matter that it was compiled from python cdk instead of CloudFormation yet these are the results I see.

This was what the CfnOutput compiled to:

"Outputs": {
  "FsxInstructionGenerationLambdaConstructFileserverip1F40FB57": {
   "Value": {
    "Fn::GetAtt": [
     "FsxInstructionGenerationLambdaConstructFsxFileServerIpRetrievalD63DD733",
     "FileServerIp"
    ]
   }
  }
 }

And this is what I had for the custom resource:

"FsxInstructionGenerationLambdaConstructFsxFileServerIpRetrievalD63DD733": {
   "Type": "AWS::CloudFormation::CustomResource",
   "Properties": {
    "ServiceToken": {
     "Fn::GetAtt": [
      "FsxInstructionGenerationLambdaConstructFsxFileServerIpRetrievalProviderframeworkonEventDE938461",
      "Arn"
     ]
    },
    "FileSystemId": "fs-06c2bba33ed9f31da"
   },
   "UpdateReplacePolicy": "Delete",
   "DeletionPolicy": "Delete"
  },

This makes CfnResource unusable for my team and unfortunately we'll have to go back to just handling the events directly until this is fixed.