Pseudo parameters are fixed parameters provided by the orchestration engine of Resource Orchestration Service (ROS). They can be referenced like user-defined parameters, and their values are determined while ROS is running.

ROS provides the following pseudo parameters:
  • ALIYUN::StackName: the name of the stack.
  • ALIYUN::StackId: the ID of the stack.
  • ALIYUN::Region: the region where the stack resides.
  • ALIYUN::AccountId: the account ID of the stack.
  • ALIYUN::TenantId: the Alibaba Cloud account ID of the stack.
  • ALIYUN::NoValue: If you use ALIYUN::NoValue for an optional property when you create or update a stack, the property will be deleted. If you use ALIYUN::NoValue for a required property, the default value of the property depends on its data type. For example, if the property is of the String type, its value will be an empty string. If the property is of the Integer type, its value will be 0. If the property is of the Array type, its value will be an empty array.
  • ALIYUN::Index: a special pseudo parameter that can only be used in the Count parameter. For more information about Count, see Count.

Examples

JSON format 

{
  "ROSTemplateFormatVersion": "2015-09-01",
  "Parameters": {
    "EnvType": {
      "Default": "pre",
      "Type": "String"
    }
  },
  "Conditions": {
    "CreateDisk": {
      "Fn::Equals": [
        "prod",
        {
          "Ref": "EnvType"
        }
      ]
    }
  },
  "Resources": {
    "WebServer": {
      "Type": "ALIYUN::ECS::Instance",
      "Properties": {
        "DiskMappings": {
          "Fn::If": [
            "CreateDisk",
            [
              {
                "Category": "cloud_efficiency",
                "DiskName": "FirstDataDiskName",
                "Size": 40
              },
              {
                "Category": "cloud_ssd",
                "DiskName": "SecondDataDiskName",
                "Size": 40
              }
            ],
            {
              "Ref": "ALIYUN::NoValue"
            }
          ]
        },
        "VpcId": "vpc-m5eebunc50zfbmts7****",
        "SystemDiskCategory": "cloud_efficiency",
        "SecurityGroupId": "sg-m5eagh7rzys2z8sa****",
        "SystemDiskSize": 40,
        "ImageId": "cent****",
        "IoOptimized": "optimized",
        "VSwitchId": "vsw-m5eem62p9729y6gps****",
        "InstanceType": "ecs.c5.large"
      }
    }
  },
  "Outputs": {
    "StackName": {
      "Value": {
        "Ref": "ALIYUN::StackName"
      }
    },
    "StackId": {
      "Value": {
        "Ref": "ALIYUN::StackId"
      }
    },
    "Region": {
      "Value": {
        "Ref": "ALIYUN::Region"
      }
    },
    "UserID": {
      "Value": {
        "Ref": "ALIYUN::AccountId"
      }
    }
  }
}

YAML format 

ROSTemplateFormatVersion: '2015-09-01'
Parameters:
  EnvType:
    Default: pre
    Type: String
Conditions:
  CreateDisk:
    Fn::Equals:
    - prod
    - Ref: EnvType
Resources:
  WebServer:
    Type: ALIYUN::ECS::Instance
    Properties:
      DiskMappings:
        Fn::If:
        - CreateDisk
        - - Category: cloud_efficiency
            DiskName: FirstDataDiskName
            Size: 40
          - Category: cloud_ssd
            DiskName: SecondDataDiskName
            Size: 40
        - Ref: ALIYUN::NoValue
      VpcId: vpc-m5eebunc50zfbmts7****
      SystemDiskCategory: cloud_efficiency
      SecurityGroupId: sg-m5eagh7rzys2z8sa****
      SystemDiskSize: 40
      ImageId: cent****
      IoOptimized: optimized
      VSwitchId: vsw-m5eem62p9729y6gps****
      InstanceType: ecs.c5.large
Outputs:
  StackName:
    Value:
      Ref: ALIYUN::StackName
  StackId:
    Value:
      Ref: ALIYUN::StackId
  Region:
    Value:
      Ref: ALIYUN::Region
  UserID:
    Value:
      Ref: ALIYUN::AccountId