Resource Orchestration Service:Resources

Property values can be text strings, lists of strings, Boolean values, referenced parameters, or function return values. When you write a JSON template, follow these rules:

• If the property value is a text string, enclose the value in double quotation marks ("").

• If the property value is a list of strings, enclose it in brackets ([]).

• If the property value is an intrinsic function or a referenced parameter, enclose it in braces ({}).

These rules also apply when you combine text, lists, referenced parameters, and function return values. The following example shows how to declare different types of property values:

{
  "Properties": {
    "String": "string",
    "LiteralList": [
      "value1",
      "value2"
    ],
    "Boolean": true,
    "ReferenceForOneValue": {
      "Ref": "ResourceID"
    },
    "FunctionResultWithFunctionParams": {
      "Fn::Join": [
        "%",
        [
          "Key=",
          {
            "Ref": "SomeParameter"
          }
        ]
      ]
    }
  }
}

When you remove resources, two situations can occur:

• If DeletionPolicy is set to Delete, the resource is deleted when it is removed from the stack.

• If DeletionPolicy is set to Retain, the resource is retained when it is removed from the stack.

For example, to retain an ECS instance when its stack is deleted, declare the policy as shown in the following code segment:

Resources:
  ECSInstance:
    Type: ALIYUN::ECS::Instance
    Properties:
      ImageId: m-25l0r****
    DeletionPolicy: Retain

Examples:

• To depend on a single resource:

  DependsOn: ResourceName

• To depend on multiple resources:

  DependsOn:
    - ResourceName1
    - ResourceName2

In the following example, the WebServer resource is created only after the DatabaseServer resource is successfully created:

ROSTemplateFormatVersion: '2015-09-01'
Resources:
  WebServer:
    Type: ALIYUN::ECS::Instance
    DependsOn: DatabseServer
  DatabseServer:
    Type: ALIYUN::ECS::Instance
    Properties:
      ImageId: m-25l0r****
      InstanceType: ecs.t1.small

In the following example, whether the WebServer resource is created is determined by the value of the MaxAmount parameter:

ROSTemplateFormatVersion: '2015-09-01'
Parameters:
  MaxAmount:
    Type: Number
    Default: 1
Conditions:
  CreateWebServer:
    Fn::Not:
      Fn::Equals:
        - 0
        - Ref: MaxAmount
Resources:
  WebServer:
    Type: ALIYUN::ECS::InstanceGroup
    Condition: CreateWebServer
    Properties:
      ImageId: m-25l0rc****
      InstanceType: ecs.t1.small
      MaxAmount:
        Ref: MaxAmount
  DatabseServer:
    Type: ALIYUN::ECS::Instance
    Properties:
      ImageId: m-25l0r****
      InstanceType: ecs.t1.small

If you specify the Count property for a resource in a template, ROS pre-processes the template and expands the resource into multiple resources. Stack operations use the processed template.

• For example, a resource is named A and its Count value is 3. In the processed template, resource A is replaced by three resources: A[0], A[1], and A[2].

  Resources:
    A:
      Count: 3
      ...

  After processing:

  Resources:
    A[0]:
      ...
    A[1]:
      ...
    A[2]:
      ...

  Important

  If the name of an expanded resource, such as A[1], already exists in the original template, the pre-processing fails and the template fails validation.

  Avoid adding the Count property to existing resources. This action changes the resource name and causes a delete operation.

• The value of the Count property must resolve to a non-negative integer. Only the following functions are supported:

  • Functions (parameter references only)

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

  • Functions

• The total number of resources in the processed template cannot exceed the limit. The current limit is 300 resources.

• In the Properties section of a resource that has the Count property, you can use the ALIYUN::Index pseudo parameter. During pre-processing, this parameter is replaced with the index of the resource replica (starting from 0). For example, the ALIYUN::Index for A[0] is replaced with 0, and the ALIYUN::Index for A[1] is replaced with 1. You cannot use ALIYUN::Index elsewhere in the template.

• If a resource with the Count property is referenced in a DependsOn property, the reference is expanded.

  DependsOn: A

  After processing:

  DependsOn:
    - A[0]
    - A[1]
    - A[2]

• If a resource with the Count property is referenced by the Ref or Fn::GetAtt function, the reference is expanded.

  Ref: A
  Fn::GetAtt:
    - A
    - PropertyName

  After processing:

  - Ref: A[0]
  - Ref: A[1]
  - Ref: A[2]
  - Fn::GetAtt:
      - A[0]
      - PropertyName
  - Fn::GetAtt:
      - A[1]
      - PropertyName
  - Fn::GetAtt:
      - A[2]
      - PropertyName

  If multiple resources use the Count property and reference each other, use Count with Fn::Select and ALIYUN::Index.

  Fn::Select:
    - Ref: ALIYUN::Index
    - Ref: A

  Take A as an example. Assume that B references A and the Count of B is 2. After the transformation, parts of the expressions for B[0] and B[1] are as follows:

  - Ref: A[0]
  - Ref: A[1]

• If a resource specifies the Count property, its DependsOn property also supports expressions. The functions that you can use in a DependsOn expression are the same as those for the Count property. You can also use the ALIYUN::Index pseudo parameter. The following table describes the expression formats and the allowed results.

  Format	Example	Allowed results
  Dictionary.	Fn::Split: - ',' - Server1,Server2	Null. If the result is null, the DependsOn property is removed.
  		A string. If the result is an empty string, the DependsOn property is removed. If the result is a non-empty string, it must be a valid resource name.
  		A list. If a list item is null or an empty string, the item is discarded. If the list becomes empty after items are discarded, the DependsOn property is removed. If the list is not empty, each item must be a string and a valid resource name.
  List.	- Server0 - Fn::Split: - ',' - Server1,Server2	The list items can be dictionaries or strings. The allowed results vary based on the item type: If a list item is a dictionary, the expression is evaluated. The allowed results are: If the result is null or an empty string, the item is discarded. Otherwise, the result must be a string and a valid resource name. If a list item is a string, it must be a valid resource name. Note If the list becomes empty after items are discarded, the DependsOn property is removed.
  String.	Server0	A string. No additional processing is performed.

  The following example template shows how to control the concurrency of resource creation when using Count. The Count parameter specifies the number of resources to create, and the ParallelCount parameter specifies the maximum number of concurrent creation operations.

  ROSTemplateFormatVersion: '2015-09-01'
  Parameters:
    Count:
      Type: Number
    ParallelCount:
      Type: Number
  Resources:
    WaitConditionHandle:
      Type: ALIYUN::ROS::WaitConditionHandle
      Count:
        Ref: Count
      DependsOn:
        Fn::Select:
          - Fn::Calculate:
              - 1-{0}//{1}
              - 0
              - - Fn::Min:
                    - Ref: ALIYUN::Index
                    - Ref: ParallelCount
                - Ref: ParallelCount
          - - Fn::Replace:
                - index:
                    Fn::Calculate:
                      - '{0}-{1}'
                      - 0
                      - - Ref: ALIYUN::Index
                        - Ref: ParallelCount
                - WaitConditionHandle[index]

  The processed template varies based on the values of Count and ParallelCount:

  • If you set Count to 3 and ParallelCount to 1, the processed template is as follows:

    ROSTemplateFormatVersion: '2015-09-01'
    Resources:
      WaitConditionHandle[0]:
        Type: ALIYUN::ROS::WaitConditionHandle
      WaitConditionHandle[1]:
        Type: ALIYUN::ROS::WaitConditionHandle
        DependsOn: WaitConditionHandle[0]
      WaitConditionHandle[2]:
        Type: ALIYUN::ROS::WaitConditionHandle
        DependsOn: WaitConditionHandle[1]
    Parameters:
      Count:
        Type: Number
      ParallelCount:
        Type: Number

  • If you set Count to 5 and ParallelCount to 2, the processed template is as follows:

    ROSTemplateFormatVersion: '2015-09-01'
    Resources:
      WaitConditionHandle[0]:
        Type: ALIYUN::ROS::WaitConditionHandle
      WaitConditionHandle[1]:
        Type: ALIYUN::ROS::WaitConditionHandle
      WaitConditionHandle[2]:
        Type: ALIYUN::ROS::WaitConditionHandle
        DependsOn: WaitConditionHandle[0]
      WaitConditionHandle[3]:
        Type: ALIYUN::ROS::WaitConditionHandle
        DependsOn: WaitConditionHandle[1]
      WaitConditionHandle[4]:
        Type: ALIYUN::ROS::WaitConditionHandle
        DependsOn: WaitConditionHandle[2]
    Parameters:
      Count:
        Type: Number
      ParallelCount:
        Type: Number

  • If you set Count to 5 and ParallelCount to 3, the processed template is as follows:

    ROSTemplateFormatVersion: '2015-09-01'
    Resources:
      WaitConditionHandle[0]:
        Type: ALIYUN::ROS::WaitConditionHandle
      WaitConditionHandle[1]:
        Type: ALIYUN::ROS::WaitConditionHandle
      WaitConditionHandle[2]:
        Type: ALIYUN::ROS::WaitConditionHandle
      WaitConditionHandle[3]:
        Type: ALIYUN::ROS::WaitConditionHandle
        DependsOn: WaitConditionHandle[0]
      WaitConditionHandle[4]:
        Type: ALIYUN::ROS::WaitConditionHandle
        DependsOn: WaitConditionHandle[1]
    Parameters:
      Count:
        Type: Number
      ParallelCount:
        Type: Number