AWS Cloudformation nested intrinsic function not evaluating - amazon-web-services

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.