这是新的《Amazon CloudFormation 模板参考指南》**。请更新您的书签和链接。有关开始使用 CloudFormation 的帮助，请参阅《Amazon CloudFormation 用户指南》[https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/Welcome.html](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/Welcome.html)。
# `Condition` 属性
要在 CloudFormation 中基于条件创建资源，首先需在模板的 `Conditions` 中声明条件。然后，在资源上使用 `Condition` 密钥以及条件的逻辑 ID 作为属性。仅当 条件评估为 true 时，CloudFormation 才会创建 资源。这样，您就可以根据模板中定义的特定标准或参数来控制资源的创建。
如果您是首次在模板中使用条件，建议您先查看《*Amazon CloudFormation 用户指南*》中有关 [CloudFormation 模板条件语法](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/conditions-section-structure.html)的内容。
**注意**
如果未创建带有条件的资源，那么所有依赖于该资源的资源也不会创建，无论它们自身的条件如何。
## 示例
以下模板包含一个具有 `Condition` 属性的 Amazon S3 存储桶字段。只有在 `CreateBucket` 条件评估为 `true` 时才会创建存储桶。
### JSON
```
{
"AWSTemplateFormatVersion" : "2010-09-09",
"Parameters" : {
"EnvType" : {
"Type" : "String",
"AllowedValues" : ["prod", "dev"],
"Default" : "dev",
"Description" : "Environment type"
}
},
"Conditions" : {
"CreateBucket" : {"Fn::Equals" : [{"Ref" : "EnvType"}, "prod"]}
},
"Resources" : {
"MyBucket" : {
"Type" : "AWS::S3::Bucket",
"Condition" : "CreateBucket",
"Properties" : {
"BucketName" : {"Fn::Join" : ["-", ["mybucket", {"Ref" : "EnvType"}]]}
}
}
}
}
```
### YAML
```
1. AWSTemplateFormatVersion: 2010-09-09
2. Parameters:
3. EnvType:
4. Type: String
5. AllowedValues:
6. - prod
7. - dev
8. Default: dev
9. Description: Environment type
10. Conditions:
11. CreateBucket: !Equals [!Ref EnvType, prod]
12. Resources:
13. MyBucket:
14. Type: AWS::S3::Bucket
15. Condition: CreateBucket
16. Properties:
17. BucketName: !Sub mybucket-${EnvType}
```
## 使用多个条件
您可以使用内置函数（如 [`Fn::And`](intrinsic-function-reference-conditions.md#intrinsic-function-reference-conditions-and)、[`Fn::Or`](intrinsic-function-reference-conditions.md#intrinsic-function-reference-conditions-or) 和 [`Fn::Not`](intrinsic-function-reference-conditions.md#intrinsic-function-reference-conditions-not)）组合多个条件，以创建更复杂的条件逻辑。
### JSON
```
{
"AWSTemplateFormatVersion" : "2010-09-09",
"Parameters" : {
"EnvType" : {
"Type" : "String",
"AllowedValues" : ["prod", "test", "dev"],
"Default" : "dev",
"Description" : "Environment type"
},
"CreateResources" : {
"Type" : "String",
"AllowedValues" : ["true", "false"],
"Default" : "true",
"Description" : "Create resources flag"
}
},
"Conditions" : {
"IsProd" : {"Fn::Equals" : [{"Ref" : "EnvType"}, "prod"]},
"IsTest" : {"Fn::Equals" : [{"Ref" : "EnvType"}, "test"]},
"CreateResourcesFlag" : {"Fn::Equals" : [{"Ref" : "CreateResources"}, "true"]},
"CreateProdResources" : {"Fn::And" : [{"Condition" : "IsProd"}, {"Condition" : "CreateResourcesFlag"}]},
"CreateTestOrDevResources" : {"Fn::And" : [{"Fn::Or" : [{"Condition" : "IsTest"}, {"Fn::Not" : [{"Condition" : "IsProd"}]}]}, {"Condition" : "CreateResourcesFlag"}]}
},
"Resources" : {
"ProdBucket" : {
"Type" : "AWS::S3::Bucket",
"Condition" : "CreateProdResources",
"Properties" : {
"BucketName" : {"Fn::Join" : ["-", ["prod-bucket", {"Ref" : "AWS::StackName"}]]}
}
},
"TestDevBucket" : {
"Type" : "AWS::S3::Bucket",
"Condition" : "CreateTestOrDevResources",
"Properties" : {
"BucketName" : {"Fn::Join" : ["-", [{"Ref" : "EnvType"}, "bucket", {"Ref" : "AWS::StackName"}]]}
}
}
}
}
```
### YAML
```
1. AWSTemplateFormatVersion: 2010-09-09
2. Parameters:
3. EnvType:
4. Type: String
5. AllowedValues:
6. - prod
7. - test
8. - dev
9. Default: dev
10. Description: Environment type
11. CreateResources:
12. Type: String
13. AllowedValues:
14. - 'true'
15. - 'false'
16. Default: 'true'
17. Description: Create resources flag
18. Conditions:
19. IsProd: !Equals [!Ref EnvType, prod]
20. IsTest: !Equals [!Ref EnvType, test]
21. CreateResourcesFlag: !Equals [!Ref CreateResources, 'true']
22. CreateProdResources: !And
23. - !Condition IsProd
24. - !Condition CreateResourcesFlag
25. CreateTestOrDevResources: !And
26. - !Or
27. - !Condition IsTest
28. - !Not [!Condition IsProd]
29. - !Condition CreateResourcesFlag
30. Resources:
31. ProdBucket:
32. Type: AWS::S3::Bucket
33. Condition: CreateProdResources
34. Properties:
35. BucketName: !Sub prod-bucket-${AWS::StackName}
36. TestDevBucket:
37. Type: AWS::S3::Bucket
38. Condition: CreateTestOrDevResources
39. Properties:
40. BucketName: !Sub ${EnvType}-bucket-${AWS::StackName}
```
## 在条件中使用 `AWS::AccountId`
您可以在条件中使用 `AWS::AccountId` 等伪参数，根据堆栈部署所在的 Amazon Web Services 账户 来创建资源。这适用于多账户部署场景，或者需要排除特定账户，不让其获取某些资源时。有关伪参数的更多信息，请参阅《*Amazon CloudFormation 用户指南*》中的[使用伪参数获取 Amazon 值](https://docs.amazonaws.cn/AWSCloudFormation/latest/UserGuide/pseudo-parameter-reference.html)。
### JSON
```
{
"AWSTemplateFormatVersion" : "2010-09-09",
"Conditions" : {
"ExcludeAccount1" : {"Fn::Not" : [{"Fn::Equals" : [{"Ref" : "AWS::AccountId"}, "111111111111"]}]},
"ExcludeAccount2" : {"Fn::Not" : [{"Fn::Equals" : [{"Ref" : "AWS::AccountId"}, "222222222222"]}]},
"ExcludeBothAccounts" : {"Fn::And" : [{"Condition" : "ExcludeAccount1"}, {"Condition" : "ExcludeAccount2"}]}
},
"Resources" : {
"StandardBucket" : {
"Type" : "AWS::S3::Bucket",
"Properties" : {
"BucketName" : {"Fn::Join" : ["-", ["standard-bucket", {"Ref" : "AWS::StackName"}]]}
}
},
"RestrictedResource" : {
"Type" : "AWS::SNS::Topic",
"Condition" : "ExcludeBothAccounts",
"Properties" : {
"TopicName" : {"Fn::Join" : ["-", ["restricted-topic", {"Ref" : "AWS::StackName"}]]}
}
}
}
}
```
### YAML
```
1. AWSTemplateFormatVersion: 2010-09-09
2. Conditions:
3. ExcludeAccount1: !Not [!Equals [!Ref 'AWS::AccountId', '111111111111']]
4. ExcludeAccount2: !Not [!Equals [!Ref 'AWS::AccountId', '222222222222']]
5. ExcludeBothAccounts: !And
6. - !Condition ExcludeAccount1
7. - !Condition ExcludeAccount2
8. Resources:
9. StandardBucket:
10. Type: AWS::S3::Bucket
11. Properties:
12. BucketName: !Sub standard-bucket-${AWS::StackName}
13. RestrictedResource:
14. Type: AWS::SNS::Topic
15. Condition: ExcludeBothAccounts
16. Properties:
17. TopicName: !Sub restricted-topic-${AWS::StackName}
```