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# `AWS::Serverless` transform
<a name="transform-aws-serverless"></a>

This topic describes how to use the `AWS::Serverless` transform to process a template written in the AWS Serverless Application Model (AWS SAM) syntax and transform it into a compliant CloudFormation template. 

For more information about using the `AWS::Serverless` transform, see [AWS SAM transform](https://github.com/aws/serverless-application-model) on GitHub.

## Usage
<a name="aws-serverless-usage"></a>

To use the `AWS::Serverless` transform, you must declare it at the top level of your CloudFormation template. You can't use `AWS::Serverless` as a transform embedded in any other template section.

The declaration must use the literal string `AWS::Serverless-2016-10-31` as its value. You can't use a parameter or function to specify a transform value.

### Syntax
<a name="aws-serverless-syntax"></a>

To declare this transform in your CloudFormation template, use the following syntax:

#### JSON
<a name="aws-serverless-syntax.json"></a>

```
{
  "Transform":"AWS::Serverless-2016-10-31",
  "Resources":{
    ...
  }
}
```

#### YAML
<a name="aws-serverless-syntax.yaml"></a>

```
Transform: AWS::Serverless-2016-10-31
Resources:
  ...
```

The `AWS::Serverless` transform is a standalone declaration with no additional parameters.

## Examples
<a name="aws-serverless-examples"></a>

The following examples show how to use the `AWS::Serverless` transform and AWS SAM syntax to simplify the declaration of a Lambda function and its execution role.

### JSON
<a name="aws-serverless-example.json"></a>

```
{
  "Transform":"AWS::Serverless-2016-10-31",
  "Resources":{
    "MyFunction":{
      "Type":"AWS::Serverless::Function",
      "Properties":{
        "Handler":"index.handler",
        "Runtime":"nodejs20.x",
        "CodeUri":"s3://amzn-s3-demo-bucket/MySourceCode.zip"
      }
    }
  }
}
```

### YAML
<a name="aws-serverless-example.yaml"></a>

```
Transform: AWS::Serverless-2016-10-31
Resources:
  MyFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: index.handler
      Runtime: nodejs20.x
      CodeUri: 's3://amzn-s3-demo-bucket/MySourceCode.zip'
```

When creating a change set from the template, CloudFormation expands the AWS SAM syntax, as defined by the transform. The processed template expands the `AWS::Serverless::Function` resource, declaring a Lambda function and an execution role.

```
{
  "Resources": {
    "MyFunction": {
      "Type": "AWS::Lambda::Function",
      "Properties": {
        "Handler": "index.handler",
        "Code": {
          "S3Bucket": "amzn-s3-demo-bucket",
          "S3Key": "MySourceCode.zip"
        },
        "Role": {
          "Fn::GetAtt": ["MyFunctionRole", "Arn"]
        },
        "Runtime": "nodejs20.x"
      }
    },
    "MyFunctionRole": {
      "Type": "AWS::IAM::Role",
      "Properties": {
        "ManagedPolicyArns": ["arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"],
        "AssumeRolePolicyDocument": {
          "Version": "2012-10-17",		 	 	 
          "Statement": [{
            "Action": ["sts:AssumeRole"],
            "Effect": "Allow",
            "Principal": {
              "Service": ["lambda.amazonaws.com"]
            }
          }]
        }
      }
    }
  }
}
```

## Using `AWS::Serverless` with `AWS::LanguageExtensions`
<a name="aws-serverless-language-extensions"></a>

When using both `AWS::Serverless` and `AWS::LanguageExtensions` transforms, referencing resources like `AWS::ApiGateway::Stage` requires special syntax when the stage name is passed as a non-`NoEcho` parameter value.

Instead of using the AWS SAM syntax for the reference (`MyApi.Stage`), use `Fn::Sub` to generate the logical ID reference. For example, `"Ref": {"Fn::Sub": "${MyApi}${StageName}Stage"}`. This builds the correct logical ID at runtime.

The reason for this special format is because these two transforms handle values differently:
+ `AWS::LanguageExtensions` resolves intrinsic functions to their actual values.
+ `AWS::Serverless` creates different logical IDs depending on whether it receives a static value or an intrinsic function.

## Related resources
<a name="aws-serverless-related-resources"></a>

For more information about serverless applications and the AWS Serverless Application Model (AWS SAM), see [AWS Serverless Application Model Developer Guide](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/what-is-sam.html).

For the resource and property types that are specific to AWS SAM, see [AWS SAM resources and properties](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-specification-resources-and-properties.html) in the *AWS Serverless Application Model Developer Guide*.

For general information about using macros, see [Perform custom processing on CloudFormation templates with template macros](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/template-macros.html) in the *AWS CloudFormation User Guide*.