AWS Cloudformation - use AWS::NoValue within Fn::Sub

user_3591169 0
Viewed 1468

I am using cloudformation and I want to be able to use the pseudo value AWS::NoValue within the Fn::Sub like this: 

!Sub ["ATL_DATASET_URL=${DatasetURL}", 
       DatasetURL: !If [IsURLProvided, 
                        !Ref BitbucketDatasetURL, 
                        !Ref "AWS::NoValue"]]

My Template passes validation but does not deploy. Here is the error message I get when I click Create Stack.

Template error: every value of the context object of every Fn::Sub object must be a string or a function that returns a string

amazon-cloudformation amazon-web-services
2 Answers

If you want to skip setting a value for DatasetURL, make the !If to return an empty string '' when the condition evaluates to false instead of AWS::NoValue.

Returning AWS::NoValue when false, removes the mapping for DatasetURL.

user_73034470

The alternative to @franklinsijo is to swap the If and Sub statements if you want to actually remove the property (e.g. YourPropertyName) if BitbucketDatasetURL is not given.

  YourPropertyName: !If
      - IsURLProvided 
      - !Sub ["ATL_DATASET_URL=${DatasetURL}", DatasetURL: !Ref BitbucketDatasetURL]
      - !Ref "AWS::NoValue"

Or shorter

  YourPropertyName: !If
      - IsURLProvided 
      - !Sub "ATL_DATASET_URL=${BitbucketDatasetURL}"
      - !Ref "AWS::NoValue"
user_2488230
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