AWS Cloudformation nested intrinsic function not evaluating

Question

This is part of the cloudformation template I am writing and getting errors using the Fn::FindInMap function:

Parameters:
  VpcStackName:
    Description: >-
      Name of an active CloudFormation VPC stack that contains the networking
      resources, such as the subnet and security group, that will be used in
      this stack.
    Type: String
    MinLength: 1
    MaxLength: 255
    AllowedPattern: '^[a-zA-Z][-a-zA-Z0-9]*$'
    Default: wordpress-dev-vpc

Mappings:
  Instance:
    development:
      AllocatedStorage: 20
      DBInstanceClass: db.t2.micro
    production:
      AllocatedStorage: 25
      DBInstanceClass: db.m3.medium

Resources:
  DBInstance:
      Type: AWS::RDS::DBInstance
      DeletionPolicy: Snapshot
      Properties:
        Engine: MariaDB
        StorageType: gp2
        MasterUsername: !Ref MasterUsername
        MasterUserPassword: !Ref MasterUserPassword
        AllocatedStorage:
          Fn::FindInMap:
            - Instance
            - Fn::ImportValue:
                Fn::Sub: '${VpcStackName}-Environment'
            - AllocatedStorage
        DBInstanceClass:
          Fn::FindInMap:
            - Instance
            - Fn::ImportValue:
                Fn::Sub: '${VpcStackName}-Environment'
            - DBInstanceClass

In another stack, I am exporting ${VpcStackName}-Environment like this:

Outputs:
  Environment:
    Description: Environment type of this stack
    Value: !Ref Environment
    Export:
      Name: !Sub '${AWS::StackName}-Environment'

When trying to use the Fn::FindInMap function, I get this error:

An error occurred (ValidationError) when calling the ValidateTemplate operation: Template error: every Fn::FindInMap object requires three parameters, the map name, map key and the attribute for return value

Any advice?

Based on the documentation at https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-findinmap.html , the supported functions inside a Fn::FindInMap function are Fn::FindInMap and Ref. So is there another way to do it? For example, storing the value of Fn::ImportValue: !Sub '${VpcStackName}-Environment' in a temporary variable?

Answer 1

According to this document, the Fn::FindInMap function is only usable with these:

• Fn::FindInMap
• Ref

So Fn::ImportValue and Fn::Sub won't be evaluated.