AWS Cloudformation嵌套的内部函数未进行评估

Question

这是我正在编写的cloudformation模板的一部分，并使用Fn::FindInMap函数收到错误：

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

在另一个堆栈中，我正在导出${VpcStackName}-Environment，如下所示：

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

尝试使用Fn::FindInMap函数时，出现此错误：

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

有什么建议吗？

根据https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/intrinsic-function-reference-findinmap.html处的文档，Fn::FindInMap函数中支持的函数为Fn::FindInMap和Ref。那还有另一种方法吗？例如，将Fn::ImportValue: !Sub '${VpcStackName}-Environment'的值存储在临时变量中？

Answer 1

根据this文档，Fn::FindInMap函数仅可用于以下功能：

• Fn::FindInMap
• 参考

因此Fn::ImportValue和Fn::Sub将不会被评估。