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AWS SAM — Serverless Application Model

Core concept: SAM is a superset of CloudFormation with shorthand syntax for serverless resources. sam build + sam deploy → CloudFormation stack.

SAM vs CloudFormation​

FeatureSAMCloudFormation
VerbosityLow (3 lines for a Lambda function)High (20+ lines)
Transforms toCloudFormationN/A
Local testing✅ sam local❌
Serverless focus✅General-purpose

SAM Template​

AWSTemplateFormatVersion: "2010-09-09"
Transform: AWS::Serverless-2016-10-31   # ← Required SAM transform

Globals:
  Function:
    Runtime: java17
    MemorySize: 512
    Timeout: 30
    Environment:
      Variables:
        TABLE_NAME: !Ref OrdersTable

Resources:

  # Simplified Lambda definition (SAM)
  OrderProcessor:
    Type: AWS::Serverless::Function    # SAM resource type
    Properties:
      Handler: com.example.OrderHandler::handleRequest
      CodeUri: target/order-service.jar
      Events:
        ApiEvent:
          Type: Api
          Properties:
            Path: /orders
            Method: POST
        SqsTrigger:
          Type: SQS
          Properties:
            Queue: !GetAtt OrderQueue.Arn
            BatchSize: 10
      Policies:
        - DynamoDBCrudPolicy:
            TableName: !Ref OrdersTable

  # SAM creates API Gateway + Lambda integration automatically
  OrdersTable:
    Type: AWS::Serverless::SimpleTable    # DynamoDB table shorthand
    Properties:
      PrimaryKey:
        Name: orderId
        Type: String

  OrderQueue:
    Type: AWS::SQS::Queue

SAM Resource Types​

SAM TypeExpands To
AWS::Serverless::FunctionLambda + IAM Role + Event Source Mappings
AWS::Serverless::ApiAPI Gateway REST API + Deployment + Stage
AWS::Serverless::HttpApiAPI Gateway HTTP API
AWS::Serverless::SimpleTableDynamoDB Table (simple PK)
AWS::Serverless::ApplicationNested application from SAR
AWS::Serverless::LayerVersionLambda Layer
AWS::Serverless::StateMachineStep Functions state machine

SAM Policy Templates​

Instead of writing full IAM policies:

Policies:
  - S3ReadPolicy:
      BucketName: !Ref MyBucket
  - DynamoDBCrudPolicy:
      TableName: !Ref MyTable
  - SQSSendMessagePolicy:
      QueueName: !GetAtt MyQueue.QueueName
  - SNSPublishMessagePolicy:
      TopicName: !GetAtt MyTopic.TopicName
  - VPCAccessPolicy: {}

SAM CLI Commands​

# Initialize new project from template
sam init

# Build (compiles Java, resolves dependencies)
sam build

# Local invoke (test single function)
sam local invoke OrderProcessor --event events/order.json

# Local API (starts local API Gateway)
sam local start-api --port 3000

# Local SQS/Kinesis simulation
sam local start-lambda

# Deploy to AWS (guided first time)
sam deploy --guided

# View CloudFormation change set before deploying
sam deploy --no-execute-changeset

# Stream logs
sam logs -n OrderProcessor --stack-name my-stack --tail

# Run unit tests
sam local invoke --event event.json

SAM for Java — sam build​

SAM understands Maven/Gradle:

# In template.yaml
OrderProcessor:
  Type: AWS::Serverless::Function
  Properties:
    CodeUri: ./          # Project root (pom.xml must be here)
    Handler: com.example.Handler::handleRequest
    Runtime: java17
    BuildMethod: maven   # or gradle
# SAM will run: mvn package -P lambda
sam build
sam local invoke

🧪 Practice Questions​

Q1. A developer wants to test a Lambda function locally with a simulated API Gateway event before deploying to AWS. What SAM CLI command should they use?

A) sam deploy --dry-run
B) sam local invoke
C) sam local start-api
D) sam test

✅ Answer & Explanation

C — sam local start-api starts a local HTTP server that simulates API Gateway and invokes the Lambda function for each request. sam local invoke is for direct function invocation without HTTP.

Q2. What is the required CloudFormation transform declaration for a SAM template?

A) Transform: AWS::SAM-2016-10-31
B) Transform: AWS::Serverless-2016-10-31
C) Version: SAM-2016
D) SAMVersion: "2016-10-31"

✅ Answer & Explanation

B — The exact string is Transform: AWS::Serverless-2016-10-31. Missing this causes the SAM resource types to be unrecognized by CloudFormation.

🔗 Resources​