Using pseudo parameters as defaults in cloudformation

Question

I'm trying to create a CloudFormation script in which I set two default parameters using AWS Pseudo-Parameters. The cloudformation validate-template cli tells me "An error occurred (ValidationError) when calling the ValidateTemplate operation: Template format error: Every Default member must be a string.

I've tried returning a string using the !Ref, !Sub, !Base64, and combinations therein. I do know you can't do two shorthands (i.e. !Base64 !Sub AWS::Region) but have to do one long and one short {i.e. Fn::Base64: !Sub AWS Region), I tried calling it as a variable in text '${AWS::Region}' and without the single quotes. Is there any way to make this work?

Here's my code as it stands now:
```
Parameters:
    BuildRegion:
        Type: String
        AllowedValues:
          - us-east-1
          - us-east-2
          - us-west-1
          - us-west-2
          - ca-central-1
          - ap-south-1
          - ap-northeast-2
          - ap-southeast-1
          - ap-southeast-2
          - ap-northeast-1
          - eu-central-1
          - eu-west-1
          - eu-west-2
          - sa-east-1
        Default: !Sub AWS::Region
    NewBucketName:
        Type: String
        Default: !Join
                    - ''
                    - - Fn::Base64:
                        - !Sub AWS::AccountId
                    - '-bucket'
```

AWS-User-5508656 · Accepted Answer

I don't think this is a supported or valid configuration.

You're using a resource Type of "string" but the default you're providing is not a "string".

Region isn't a valid AWS special parameter type to be used in Resource:
http://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/parameters-section-structure.html#aws-specific-parameter-types

To move forward you will probably need to pick a default value from your AllowedValues (like "us-east-1").  Slightly less convenient than having the current region populated.

As an aside - CloudFormation doesn't operate cross region.  So if you're intending to use this region parameter later during resource creation it probably won't work!

Using pseudo parameters as defaults in cloudformation

Contenuto pertinente