For anyone working with YAML …

For anyone working with YAML Cloud Formation, if you were to see this error message:

E0001 Error transforming template: 'NoneType' object has no attribute 'get'
cloudformation.yaml:1:1

it might be because one of your resources is not properly indented. That is, the Type and Properties keyword is at the same indentation level as the resource name:

Resources:
  # Broken
  DeadLetterQueue:
  Type: AWS::SQS::Queue
  Properties:
    # ...

  # Fixed
  DeadLetterQueue:
    Type: AWS::SQS::Queue
    Properties:
      # ...

Another problem is that you’re trying to use !GetAtt with a string parameter:

Parameters:
  DynamoDBStream:
    Type: String

Resources:
  LambdaDynamoStream:
    Type: AWS::Lambda::EventSourceMapping
    Properties:
      # This is the source of your woes 
      EventSourceArn: !GetAtt DynamoDBStream.StreamArn

Took a while for me to find the cause of these. Had to comment out all the resources and uncomment them back one by one. In retrospect, a quick glance at the entire file would’ve found it as well; although the slow act of going through the file, commenting and uncommenting things, was still a useful act in and of itself.

Naturally the error message is cryptic, probably because it falls within the gap of a well-formed YAML file but a badly formed object model. Some better error reporting would be preferred though.

And yeah, there’s going to be commentary about error reporting in these posts. 😛