Conditions

Syntax

The declaration of a condition consists of a condition name and a condition statement. The condition name is of the String type. You can use the following functions to define condition statements. You can reference other conditions in a condition. Each condition name must be unique.

• Fn::And

• Fn::Or

• Fn::Not

• Fn::Equals

You can use the following functions to define conditions, but cannot use the functions as the outermost functions:

"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"(only for parameter references), and "Fn::FindInMap".

Examples

• The following example shows how to define 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         

• The following example shows how to associate conditions with resources.

  In this example, the EnvType value is used as a condition to determine whether to create a data disk and an Object Storage Service (OSS) bucket for an Elastic Compute Service (ECS) instance.

  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