Resource Orchestration Service:Resources

A property value can be a text string, a list of strings, a Boolean value, a referenced parameter, or a function return value. When you write a JSON template, you must 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 the list in square 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 property value types:

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

When you remove a resource, two scenarios are possible:

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

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

For example, to keep an ECS instance when the 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

The following examples show two ways to use this attribute:

• Dependency on a single resource:

  DependsOn: ResourceName

• Depend on multiple resources:

  DependsOn:
    - ResourceName1
    - ResourceName2

As shown in the following code segment, WebServer is created only after DatabaseServer 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

As shown in the following code segment, the creation of WebServer depends on the value of MaxAmount:

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

In a template, after you specify Count for a resource, ROS pre-processes the template and expands the resource into multiple resources. The processed template is then used when you perform operations on the stack.

• For example, if a resource is named A and its Count value is 3, the processed template will not contain the A resource. Instead, it will contain 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 does not pass validation.

  Avoid adding the Count attribute to existing resources. This changes the resource name and triggers a delete operation.

• The final result of Count must be a natural number. Only the following functions are supported:

  • Ref (references parameters only)

  • Fn::FindInMap

  • Fn::Select

  • Fn::Join

  • Fn::Split

  • Fn::Replace

  • Fn::Base64Encode

  • Fn::Base64Decode

  • Fn::If

  • Fn::ListMerge

  • Fn::GetJsonValue

  • Fn::MergeMapToList

  • Fn::SelectMapList

  • Fn::Add

  • Fn::Avg

  • Fn::Str

  • Fn::Calculate

  • Fn::Max

  • Fn::Min

• The total number of resources in the processed template must not exceed the limit, which is currently 300.

• In the Properties of a resource with Count specified, you can use the pseudo parameter ALIYUN::Index. During pre-processing, this parameter is replaced with the corresponding number. For example, the ALIYUN::Index used by A[0] is replaced with 0, and the ALIYUN::Index used by A[1] is replaced with 1. You cannot use ALIYUN::Index elsewhere in the template.

• If a resource with Count specified appears in DependsOn, it is expanded.

  DependsOn: A

  After processing:

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

• If a resource with Count specified appears in the Ref or Fn::GetAtt function, it 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 Count and have reference relationships, you can use them with Fn::Select and ALIYUN::Index.

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

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

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

• If a resource has the Count attribute, the DependsOn attribute also supports expressions. The functions that can be used in the DependsOn expression are the same as those for the Count attribute, and you can use the ALIYUN::Index pseudo parameter. The following table describes the format of the expression and the allowed calculation results.

  Format	Example	Allowed calculation result
  Dictionary	Fn::Split: - ',' - Server1,Server2	null If the value is null, the DependsOn attribute is removed.
  		String If the value is an empty string, the DependsOn attribute is removed. If the value is a non-empty string, it must be a valid resource name.
  		List If a list item is null or an empty string, the item is discarded. If the list is empty, the DependsOn attribute 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	A list item can be a dictionary or a string. The allowed calculation results vary based on the item type: If the list item is a dictionary, the expression is calculated. The allowed calculation results are as follows: If the value is null or an empty string, the item is discarded. Otherwise, it must be a string and a valid resource name. If the list item is a string, it must be a valid resource name. Note If the list is empty, the DependsOn attribute is removed.
  String	Server0	String No additional processing is performed.

  The following example template controls the concurrency for resources created with Count. The Count parameter specifies the number of resources to create, and the ParallelCount parameter specifies the maximum number of concurrent creations.

  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