CloudFormation Fn::Transform Operation: Lower -> syntax error

user_2925814 0
Viewed 1125

I'm trying to create an AWS S3 Bucket with cloud formation.

S3 bucket name needs to be lowercase but I want to use a paramenter to compound that name. This parameter comes uppercase.

I founded a way.

I read this.

This is my code:

Parameters:

# Global
  ServiceName:
    Type: String
    Description: 'Service Name'
    Default: content-input
   
  Environment:
    Type: String
    Description: 'Environment Name'

Resources:
  S3Bucket: 
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Join ['-',
      [ 
        content-input,
        'Fn::Transform':
          - Name: 'String'
          Parameters: 
            InputString: !Ref Environment
            Operation: Lower
      ]]

But I get this error.

while parsing a flow node
expected the node content, but found '-'
  in "<unicode string>", line 157, column 11:
              - Name: 'String'

I tried this other syntax referered here

Parameters:

# Global
  ServiceName:
    Type: String
    Description: 'Service Name'
    Default: content-input
   
  Environment:
    Type: String
    Description: 'Environment Name'

Resources:
  S3Bucket: 
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Join ['-',
      [ 
        content-input,
        'Fn::Transform':
          Name: 'String'
          Parameters: 
            InputString: !Ref Environment
            Operation: Lower
      ]]

But I get:

while parsing a flow sequence
  in "<unicode string>", line 154, column 7:
          [
          ^
expected ',' or ']', but got ':'
  in "<unicode string>", line 157, column 15:
              Name: 'String'
                  ^

Of Course, this work perfectly.

Parameters:

# Global
  ServiceName:
    Type: String
    Description: 'Service Name'
    Default: content-input
   
  Environment:
    Type: String
    Description: 'Environment Name'

Resources:
  S3Bucket: 
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Join ['-',
      [ 
        content-input,
        mytext
      ]]

How is the right syntax?

amazon-cloudformation amazon-web-services amazon-s3
1 Answers

Important point to note to get the syntax right is to use Json with Yaml when using multiple Intrinsic functions. Updated syntax below. For Environment value DEV, this creates a bucket of name content-input-dev

AWSTemplateFormatVersion: "2010-09-09"
Parameters:
  ServiceName:
    Type: String
    Description: "Service Name"
    Default: content-input
  Environment:
    Type: String
    Description: "Environment Name"
Resources:
  S3Bucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName:
        !Join [
          "-",
          [
            !Ref ServiceName,
            {
              "Fn::Transform":
                {
                  "Name": "String",
                  "Parameters":
                    { "InputString": !Ref Environment, "Operation": "Lower" },
                },
            },
          ],
        ]
user_101868080
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