CFN template: how to use Type List using VPC ids?

Question

i know it's allowed to have a list of VPC as params

I would like to add a default value, choosing the one I exported from another stack

```
  VPC:
    Type: List
    Default:
      - !ImportValue Network-V1-VPC
```

I kindly ask you how can I be sure user is choosing only ONE element?

And how can I use the selected value (or the first one if multiple if I cannot avoid this) ?

Answer

Hello.

As of May 2024, CloudFromation built-in functions cannot be used in the parameters section.  
This means that the "!ImportValue" function cannot be used in the parameter section.  
Therefore, the template you are trying to use will result in an error.  
https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference.html  
> You can use intrinsic functions only in specific parts of a template. Currently, you can use intrinsic functions in resource properties, outputs, metadata attributes, and update policy attributes. You can also use intrinsic functions to conditionally create stack resources.

CFN template: how to use Type List using VPC ids?

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