Resource Orchestration Service:Conditions

Syntax

How conditions work

To use conditions in a template, follow these steps:

1. Define input parameters — Declare the values your conditions will evaluate in the Parameters section.

2. Define conditions — Write condition statements in the Conditions section using the supported condition functions listed below. Each condition name must be unique and is of the String type. Conditions can reference other conditions.

3. Associate conditions with resources or outputs — Reference conditions in the Resources section (via Condition key or Fn::If) and in the Outputs section (via Condition key) to control what gets created.

Condition functions

Use the following functions to define condition statements:

• Fn::And

• Fn::Or

• Fn::Not

• Fn::Equals

The following functions are supported inside condition statements but cannot be the outermost function in a condition:

Fn::Select, Fn::Join, Fn::Split, Fn::Replace, Fn::Base64Encode, Fn::Base64Decode, Fn::MemberListToMap, Fn::If, Fn::ListMerge, Fn::GetJsonValue, Fn::MergeMapToList, Fn::SelectMapList, Fn::Add, Fn::Avg, Fn::Str, Fn::Calculate, Ref (parameter references only), and Fn::FindInMap.

Examples

• Define conditions

  The following example defines four conditions based on an EnvType parameter. DevEnv and UTEnv each check for a specific environment value. PREEnv is true when neither DevEnv nor UTEnv is true. ProdEnv combines an equality check with PREEnv using Fn::And, showing how to compose conditions from other conditions.

  Conditions:
    DevEnv:
      Fn::Equals:
        - Dev
        - Ref: EnvType
    UTEnv:
      Fn::Equals:
        - UT
        - Ref: EnvType
    PREEnv:
      Fn::Not:
        Fn::Or:
          - DevEnv
          - UTEnv
    ProdEnv:
      Fn::And:
        - Fn::Equals:
            - Prod
            - Ref: EnvType
        - PREEnv         

• Associate conditions with resources and outputs

  The following example uses EnvType to control resource creation. When EnvType is prod, the template creates data disks for the Elastic Compute Service (ECS) instance and provisions an Object Storage Service (OSS) bucket. When EnvType is any other value, neither the data disks nor the OSS bucket are created, and the corresponding output is suppressed. The example demonstrates three ways to use a condition: - Fn::If on a property value — Conditionally sets DiskMappings on the ECS instance (WebServer). - Condition key on a resource — Gates creation of the entire OssBucket resource. - Condition key on an output — Suppresses OssDomain when the bucket does not exist.

  ROSTemplateFormatVersion: '2015-09-01'
  Parameters:
    EnvType:
      Default: pre
      Type: String
  Conditions:
    CreateProdRes:
      Fn::Equals:
        - prod
        - Ref: EnvType
  Resources:
    WebServer:
      Type: ALIYUN::ECS::Instance
      Properties:
        DiskMappings:
          Fn::If:
            - CreateProdRes
            - - Category: cloud_efficiency
                DiskName: FirstDataDiskName
                Size: 40
              - Category: cloud_ssd
                DiskName: SecondDataDiskName
                Size: 40
            - Ref: ALIYUN::NoValue
        VpcId: vpc-2zew9pxh2yirtzqxd****
        SystemDiskCategory: cloud_efficiency
        SecurityGroupId: sg-2zece6wcqriejf1v****
        SystemDiskSize: 40
        ImageId: centos_6_8_64_40G_base_2017****.vhd
        IoOptimized: optimized
        VSwitchId: vsw-2zed9txvy7h2srqo6****
        InstanceType: ecs.n1.medium
    OssBucket:
      Type: ALIYUN::OSS::Bucket
      Condition: CreateProdRes
      Properties:
        AccessControl: private
        BucketName: myprodbucket
  Outputs:
    InstanceId:
      Value:
        Fn::GetAtt:
          - WebServer
          - InstanceId
    OssDomain:
      Condition: CreateProdRes
      Value:
        Fn::GetAtt:
          - OssBucket
          - DomainName