AWS SAM (Serverless Application Model)

The AWS Serverless Application Model (SAM) is an open-source framework for building serverless applications on AWS. It extends CloudFormation with simplified syntax for defining Lambda functions, API Gateway APIs, DynamoDB tables, and other serverless resources. SAM also includes a CLI for local development, testing, and deployment.

---

Why SAM?

Building serverless applications with raw CloudFormation is verbose. A single Lambda function with an API Gateway trigger requires dozens of lines of CloudFormation. SAM reduces this to a few lines:

CloudFormation (without SAM) — ~80 lines

# You need to define:
# - AWS::Lambda::Function
# - AWS::Lambda::Permission
# - AWS::ApiGateway::RestApi
# - AWS::ApiGateway::Resource
# - AWS::ApiGateway::Method
# - AWS::ApiGateway::Deployment
# - AWS::ApiGateway::Stage
# - AWS::IAM::Role
# - AWS::IAM::Policy
# ... plus wiring them all together

SAM — ~15 lines

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Resources:
  HelloFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: index.handler
      Runtime: nodejs20.x
      Events:
        HelloApi:
          Type: Api
          Properties:
            Path: /hello
            Method: get

SAM's Transform: AWS::Serverless-2016-10-31 directive tells CloudFormation to expand SAM resources into full CloudFormation resources at deployment time.

---

SAM CLI

The SAM CLI is the command-line tool for building, testing, and deploying SAM applications: