GetAtt returns a string value instead of an array when a parameter of a Fn::Select

[CPMellows]

Upon using the --resolve flag on a template containing a Select that retrieves its array using a GetAtt, the Attribute returned is a single value instead of an array.

I'm able to get the Error to disappear by creating a parameter file containing the object
{"ApiGatewayEndpoint":{"DnsEntries":["String"]}}
But as my use case is as a general scanning tool for checking in code defining every Ref in a prameters file and using --resolve-parameters isn't an option.

Template

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "The AWS CloudFormation template for this Serverless application",
  "Resources": {
    "UsageRetryLambdaFunction": {
      "Type": "AWS::Lambda::Function",
      "Properties": {
        "Code": {
          "S3Bucket": "Bucket",
          "S3Key": "retry-lambda/function.zip"
        },
        "Runtime": "java11",
        "FunctionName": "Retry-Lambda",
        "MemorySize": 512,
        "Timeout": 300,
        "KmsKeyArn": "arn:aws:kms:ap-south-1:123456789012:key/a-key",
        "Environment": {
          "Variables": {
            "API_ENDPOINT": {
              "Fn::Join": [
                "",
                [
                  "https://",
                  {
                    "Fn::Select": [
                      "1",
                      {
                        "Fn::Split": [
                          ":",
                          {
                            "Fn::Select": [
                              "0",
                              {
                                "Fn::GetAtt": [
                                  "ApiGatewayEndpoint",
                                  "DnsEntries"
                                ]
                              }
                            ]
                          }
                        ]
                      }
                    ]
                  },
                  "/prod/api/usage"
                ]
              ]
            },
            "API_ID": "asdfghghjk",
            "HTTP_RETRY": "3"
          }
        },
        "Role": "arn:aws:iam::123456789012:role/retry-prod-ap-south-1-lambdaRole",
        "VpcConfig": {
          "SecurityGroupIds": ["sg-123456789"],
          "SubnetIds": [
            {
              "Fn::ImportValue": "PrivateA-SubnetID"
            },
            {
              "Fn::ImportValue": "PrivateB-SubnetID"
            }
          ]
        },
        "ReservedConcurrentExecutions": 10
      }
    },
    "ApiGatewayEndpoint": {
      "Type": "AWS::EC2::VPCEndpoint",
      "Properties": {
        "ServiceName": {
          "Fn::Sub": "com.amazonaws.us-east-1.execute-api"
        },
        "SecurityGroupIds": [
          {
            "Ref": "VpcEndpointSecurityGroup"
          }
        ],
        "SubnetIds": ["subnet-111111", "subnet-222222", "subnet-333333"],
        "VpcId": "vpc-1234567",
        "VpcEndpointType": "Interface"
      }
    }
  }
}

Output

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/cfripper/cli.py", line 222, in cli
    results_of_templates = [
  File "/usr/local/lib/python3.9/site-packages/cfripper/cli.py", line 223, in <listcomp>
    process_template(template=template, resolve_parameters=resolve_parameters, **kwargs)
  File "/usr/local/lib/python3.9/site-packages/cfripper/cli.py", line 119, in process_template
    cfmodel = cfmodel.resolve(resolve_parameters)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/model/cf_model.py", line 87, in resolve
    resolved_resources = {
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/model/cf_model.py", line 88, in <dictcomp>
    key: resolve(value, extended_parameters, self.Mappings, resolved_conditions)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 54, in resolve
    resolved_value = resolve(v, params, mappings, conditions)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 54, in resolve
    resolved_value = resolve(v, params, mappings, conditions)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 54, in resolve
    resolved_value = resolve(v, params, mappings, conditions)
  [Previous line repeated 1 more time]
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 50, in resolve
    return function_resolver(function[function_name], params, mappings, conditions)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 84, in resolve_join
    resolved_list = resolve(list_values, params, mappings, conditions)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 41, in resolve
    resolved_value = resolve(entry, params, mappings, conditions)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 50, in resolve
    return function_resolver(function[function_name], params, mappings, conditions)
  File "/usr/local/lib/python3.9/site-packages/pycfmodel/resolver.py", line 125, in resolve_select
    return resolved_list[resolved_index]
IndexError: list index out of range

[oscarbc96]

Hey!
We don't have the Fn::GetAtt function implemented at the moment.

pycfmodel/pycfmodel/resolver.py

Line 169 in cd579da

logger.warning("`Fn::GetAtt` resolver not implemented, returning `GETATT`")

GetAtt has to return values that are only known when the resource is deployed.