How to Fn::Split append an existing array?-CodePudding

I have an IAM role with existing managed policies that I need to add more managed policies via a parameter since they're dynamic per stack.

Here's what I tried/want but it doesn't work. The cloudformation event error is "Value of property ManagedPolicyArns must be of type List of String". I take that to mean that the Split doesn't append the array but rather adds one item to the array that is itself an array.

Parameters:
  StackManagedPolicyArns:
    Description: Comma separated, dynamic list of ARNs passed in when deploying
    Type: String
    
Resources:
  MyRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: !Sub "${AWS::StackName}"
      ManagedPolicyArns:
        - Fn::ImportValue: !Sub "${Namespace}-common-policy"
        - Fn::Split:
            - ','
            - !Ref StackManagedPolicyArns

How can I accomplish this?

CodePudding user response：

Things like that in CFN are a bit tricky. But you can join first everything into one large string, and then split it into array. This requires a combo of Join and Split functions:

Resources:
  MyRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: !Sub "${AWS::StackName}"
      ManagedPolicyArns:        
        Fn::Split:
          - ','
          - Fn::Join:
            - ","
            - - Fn::ImportValue: !Sub "${Namespace}-common-policy"
              - Fn::Join:
                 - ","
                 - !Split [',', !Ref StackManagedPolicyArns]