AWS cloudformation error: Template validation error: Template error: resource NotificationsTopic does not support attribute type Arn in Fn::GetAtt

Question

I am trying to create an AWS cloudformation stack using a yaml template. The goal is to create a sns topic for some notifications. I want to output the topic arn, to be able to subscribe multiple functions to that topic by just specifying the topic arn.

However I am getting an error when I try to create the stack from the aws console:

"Template validation error: Template error: resource NotificationsTopic does not support attribute type Arn in Fn::GetAtt"

I have done exactly the same for s3 buckets, dynamodb tables, and all working good, but for some reason, with SNS topic I cannot get the ARN.

I want to avoid hardcoding the topic arn in all functions that are subscribed. Because if one day the the ARN topic changes, I'll need to change all functions, instead I want to import the topic arn in all functions and use it. This way I will have to modify nothing if for any reason I have a new arn topic in the future.

This is the template:

    Parameters:
  stage:
    Type: String
    Default: dev
    AllowedValues:
      - dev
      - int
      - uat
      - prod

Resources:
   NotificationsTopic:
        Type: AWS::SNS::Topic
        Properties:
          DisplayName: !Sub 'notifications-${stage}'
          Subscription:
            - SNS Subscription
          TopicName: !Sub 'notifications-${stage}'
Outputs:
  NotificationsTopicArn:
    Description: The notifications topic Arn.
    Value: !GetAtt NotificationsTopic.Arn
    Export:
      Name: !Sub '${AWS::StackName}-NotificationsTopicArn'
  NotificationsTopicName:
    Description: Notifications topic name.
    Value: !Sub 'notifications-${stage}'
    Export:
      Name: !Sub '${AWS::StackName}-NotificationsTopicName'

Answer 1

Not all resources are the same. Always check the documentation for the particular resource. It has the "Return Values" section and you can easily verify that SNS topic has ARN as a Ref value, so you don't have to use GetAtt function

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-sns-topic.html