Parameters

Syntax

Each parameter consists of a name and properties. The parameter name can contain only letters and digits, and must be unique within the template. You can use the Label field to define the alias of a parameter.

The following table describes the parameter properties.

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Example 1: the InstanceType parameter that is used to create a stack in a web application

For example, you want to create a stack in a web application, and the stack needs to contain one Server Load Balancer (SLB) instance, two ECS instances, and one ApsaraDB RDS instance. If the web application is under heavy workload, you can select an ECS instance that has high specifications when you create the stack. If the web application is not under heavy workload, you can select an ECS instance that has lower specifications. The following example shows how to define the InstanceType parameter for an ECS instance:

"Parameters" : {
  "InstanceType" : {
    "Type" : "String",
    "AllowedValues":["ecs.t1.small","ecs.s1.medium", "ecs.m1.medium", "ecs.c1.large"],
    "Default": "ecs.t1.small",
    "Label": "The ECS instance type",
    "Description": "The type of the ECS instance that you want to create. Default value: ecs.t1.small. Valid values: ecs.t1.small, ecs.s1.medium, ecs.m1.medium, and ecs.c1.large."
  }
}

You can specify the value of the InstanceType parameter when you create stacks based on the template. If you do not specify the parameter, the default value ecs.t1.small is used.

The following example shows how to reference the InstanceType parameter when you define a resource:

"Webserver" : {
  "Type" : "ALIYUN::ECS::Instance",
  "InstanceType": {
    "Ref": "InstanceType"
  }
}

Example 2: the UserName, PassWord, and ImageId parameters

In the following example, three parameters are defined in the Parameters section.

• UserName: a String-type parameter whose value must be 6 to 12 characters in length. Default value: anonymous. Valid values:
  • anonymous
  • user-one
  • user-two
  Note The default value anonymous must also meet the length and valid value requirements.
• PassWord: a String-type parameter that does not have a default value. If you set the NoEcho parameter property to true, the GetStack operation does not return parameter values. The parameter value must be 1 to 41 characters in length and can contain uppercase letters, lowercase letters, and digits.
• ImageId: a String-type parameter. You can use the AssociationProperty parameter property to query the list of all available images and check whether the default value is valid.

"Parameters": {
  "UserName": {
    "Label": "Username",
    "Description": "Enter the username",
    "Default": "anonymous",
    "Type": "String",
    "MinLength": "6",
    "MaxLength": "12",
    "AllowedValues": [
      "anonymous",
      "user-one",
      "user-two"
    ]
  },
  "PassWord": {
    "Label": "Password",
    "NoEcho": "True",
    "Description": "Enter the password",
    "Type": "String",
    "MinLength": "1",
    "MaxLength": "41",
    "AllowedPattern": "[a-zA-Z0-9]*"
  },
  "ImageId": {
    "Label": "Image",
    "Type": "String",
    "Description": "Select an image",
    "AssociationProperty": "ALIYUN::ECS::Instance::ImageId",
    "Default": "centos_7_7_x64_20G_alibase_2020****.vhd"
  }
}

Example 3: the VSwitchId parameter that uses the AssociationPropertyMetadata parameter property

If you specify the AssociationPropertyMetadata parameter property, the ROS console lists available vSwitches in a drop-down list that are located in the specified zone and VPC. If you do not specify the AssociationPropertyMetadata parameter property, the ROS console lists all vSwitches in the current region.

{
  "ROSTemplateFormatVersion": "2015-09-01",
  "Parameters": {
    "VpcId": {
      "Type": "String",
      "AssociationProperty": "ALIYUN::ECS::VPC::VPCId"
    },
    "EcsZone": {
      "Type": "String",
      "AssociationProperty": "ALIYUN::ECS::Instance::ZoneId"
    },
    "VSwitchId": {
      "Type": "String",
      "AssociationProperty": "ALIYUN::ECS::VSwitch::VSwitchId",
      "AssociationPropertyMetadata": {
        "VpcId": "VpcId",
        "ZoneId": "EcsZone"
      }
    }
  }
}