CloudFormation User Parameter as another parameter Default Value

Question

Hello,

I keep getting this error

`Template Format error parameter default has to be string
`
and i want to use a Parameter as another Parameter Default.
```
Parameters:
  AppId:
    Type: String
    Default: "mygradecard-iac"
  RepositoryName:
    Type: String
    Default: !Sub "${AppId}-Respository"
    Description: "Name of the Repository to be Created"

```
Thank you

Accepted Answer

Hi,

You cannot do that so directly: as said by the message, a parameter is a string, you cannot call something like !Sub in a parameter defintion

But, there are solutions: I personally use SSM parameters to achieve what you want.  See https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-ssm-parameter.html

```
BasicParameter:
    Type: AWS::SSM::Parameter
    Properties:
      Name: MyParam
      Type: String
      Value: 'xyz'
      Description: SSM Parameter for running date command.
```

In  `Value`, you can use !Sub or any function.

Then, you obtain your value by calling !GetAtt MyParam.Value. Additional advantage, the SSM console will allow you to easily see the result of your value computation.

It works great for me. I wish that it will be same for you.

Best,

Didier

CloudFormation User Parameter as another parameter Default Value

Relevant content