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使用以下 yaml 时出现错误。我检查了代码，但我不认为有任何问题。我的结构计划有一个带有 2 个公有子网和 2 个私有子网的 VPC。一个Web服务器实例将放置在公共子网2中。我认为该问题可能与实例创建有关，因为该错误是在实例创建过程中出现的。

Parameters:
  EnvironmentName:
    Description: An environment name that is prefixed to resource names
    Type: String

  KeyName:
    Description: Name of an existing EC2 KeyPair to enable SSH access to the instances
    Type: AWS::EC2::KeyPair::KeyName
    ConstraintDescription: must be the name of an existing EC2 KeyPair.

  SSHLocation:
    Description: The IP address range that can be used to SSH to the EC2 instances
    Type: String
    MinLength: '9'
    MaxLength: '18'
    Default: 0.0.0.0/0
    AllowedPattern: "(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})/(\\d{1,2})"
    ConstraintDescription: must be a valid …