{
  "Resources": {
    "AWSConfigRule": {
      "Type": "AWS::Config::ConfigRule",
      "Properties": {
        "ConfigRuleName": {
          "Ref": "ConfigRuleName"
        },
        "Description": "Checks whether your EC2 instances are of the specified instance types.",
        "InputParameters": {
          "instanceType": {
            "Fn::If": [
              "instanceType",
              {
                "Ref": "instanceType"
              },
              {
                "Ref": "AWS::NoValue"
              }
            ]
          }
        },
        "Scope": {
          "ComplianceResourceTypes": [
            "AWS::EC2::Instance"
          ]
        },
        "Source": {
          "Owner": "AWS",
          "SourceIdentifier": "DESIRED_INSTANCE_TYPE"
        }
      }
    }
  },
  "Parameters": {
    "ConfigRuleName": {
      "Type": "String",
      "Default": "desired-instance-type",
      "Description": "The name that you assign to the AWS Config rule.",
      "MinLength": "1",
      "ConstraintDescription": "This parameter is required."
    },
    "instanceType": {
      "Type": "String",
      "Description": "Comma separated list of EC2 instance types (for example, \u0027t2.small, m4.large\u0027).",
      "MinLength": "1",
      "ConstraintDescription": "This parameter is required."
    }
  },
  "Metadata": {
    "AWS::CloudFormation::Interface": {
      "ParameterGroups": [
        {
          "Label": {
            "default": "Required"
          },
          "Parameters": [
            "instanceType"
          ]
        },
        {
          "Label": {
            "default": "Optional"
          },
          "Parameters": []
        }
      ]
    }
  },
  "Conditions": {
    "instanceType": {
      "Fn::Not": [
        {
          "Fn::Equals": [
            "",
            {
              "Ref": "instanceType"
            }
          ]
        }
      ]
    }
  }
}