Which resource does AWS serverless application model syntax expand and transform into?

AWS::Serverless transform

The AWS::Serverless transform, which is a macro hosted by CloudFormation, takes an entire template written in the AWS Serverless Application Model (AWS SAM) syntax and transforms and expands it into a compliant CloudFormation template. For more information about serverless applications and AWS SAM, see Deploying Lambda-based applications in the AWS Lambda Developer Guide and AWS SAM resource and property reference in the AWS Serverless Application Model Developer Guide.

In the following example, the template uses AWS SAM syntax to simplify the declaration of a Lambda function and its execution role.

Transform: AWS::Serverless-2016-10-31
Resources:
  MyServerlessFunctionLogicalID:
    Type: AWS::Serverless::Function
    Properties:
      Handler: index.handler
      Runtime: nodejs8.10
      CodeUri: 's3://testBucket/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 an AWS Lambda function and an execution role.

{
  "Resources": {
    "MyServerlessFunctionLogicalID": {
      "Type": "AWS::Lambda::Function",
      "Properties": {
        "Handler": "index.handler",
        "Code": {
          "S3Bucket": "testBucket",
          "S3Key": "mySourceCode.zip"
        },
        "Role": {
          "Fn::GetAtt": ["FunctionNameRole", "Arn"]
        },
        "Runtime": "nodejs8.10"
      }
    },
    "FunctionNameRole": {
      "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"]
            }
          }]
        }
      }
    }
  }
}

Syntax

The value for the transform declaration must be a literal string. You can't use a parameter or function to specify a transform value. The following snippet is an example of a transform declaration:

JSON

"Transform" : "AWS::Serverless-2016-10-31"

YAML

Transform: "AWS::Serverless-2016-10-31"