AWS SAM (Serverless Application Model) – DVA-C02 Essentials

What is AWS SAM?

AWS SAM (Serverless Application Model) is an extension of AWS CloudFormation used to build and deploy serverless applications easily.

Instead of writing many CloudFormation resources, you write a few simple SAM resources, and SAM generates the CloudFormation for you.

Think:

SAM = Simplified CloudFormation for Serverless

SAM Deployment Workflow

For the exam, remember this sequence:

Write template.yaml
        ↓
sam build
        ↓
sam deploy --guided (first time)
        ↓
CloudFormation creates AWS resources

sam build

Purpose:

• Compiles application
• Installs dependencies
• Prepares deployment artifacts
• Creates .aws-sam/ folder

Example:

sam build

Remember:

Build prepares the application.

It does NOT deploy anything.

sam deploy

Purpose:

• Packages code
• Uploads artifacts to S3
• Creates/updates CloudFormation stack
• Deploys Lambda, API Gateway, DynamoDB, etc.

Example:

sam deploy --guided

First deployment:

sam deploy --guided

Later deployments:

sam deploy

Remember:

Deploy sends the application to AWS.

sam local invoke

Purpose:

Run Lambda locally.

Example:

sam local invoke

Important:

It

• does NOT deploy
• does NOT upload code
• does NOT create AWS resources

Exam trick:

Local Invoke = Testing only

SAM uses CloudFormation

SAM templates are transformed into CloudFormation.

Deployment automatically creates:

• Lambda
• API Gateway
• IAM Roles
• Permissions
• Event mappings

No manual CloudFormation creation required.

Globals Section

Large SAM templates often repeat:

• Runtime
• Timeout
• Memory
• Environment Variables

Instead of repeating them, use:

Globals:
  Function:
    Runtime: python3.12
    Timeout: 30
    MemorySize: 256

Every Lambda automatically inherits these values.

Individual functions can still override them.

Example:

Globals:
  Function:
    Runtime: python3.12
    Timeout: 30

Resources:

  FunctionA:
    Type: AWS::Serverless::Function

  FunctionB:
    Type: AWS::Serverless::Function

Both automatically use:

• python3.12
• 30 sec timeout

No repetition.

Exam tip:

Globals = Default settings for all functions.

AWS::Serverless::Function

Basic Lambda definition:

Resources:

  HelloFunction:
    Type: AWS::Serverless::Function

SAM converts this into normal CloudFormation resources.

Events Section

Example:

Events:

  MyAPI:
    Type: HttpApi

This small block automatically creates:

• HTTP API Gateway
• Route
• Lambda integration
• Lambda permissions

You do NOT manually create these resources.

Remember:

Events generate the event source automatically.

HttpApi Event

When using:

Type: HttpApi

SAM creates:

• HTTP API Gateway
• Routes
• Integration
• Lambda permissions

It does NOT create:

• Custom domain
• REST API

Unless you define them separately.

HTTP API vs REST API

HTTP API

• Faster
• Cheaper
• Simpler
• API Gateway V2

REST API

• Older
• More features
• More expensive

If SAM Event Type is:

HttpApi

SAM creates an HTTP API, not a REST API.

Automatic Resources Created by SAM

When deploying:

AWS::Serverless::Function

with

Events:
    Type: HttpApi

SAM automatically creates:

• Lambda
• HTTP API
• Route
• Integration
• Invoke permission

You only write a few lines.

Common Exam Traps

Trap

sam build deploys application.

❌ False

It only prepares artifacts.

Trap

sam local invoke deploys Lambda.

❌ False

Runs locally only.

Trap

Need to manually create CloudFormation stack.

❌ False

sam deploy creates the stack.

Trap

Globals cannot be overridden.

❌ False

Individual functions can override inherited values.

Trap

HttpApi creates REST API.

❌ False

Creates HTTP API Gateway (API Gateway V2).

Quick Exam Memory Sheet

Build

• Compile code
• Install dependencies
• Prepare artifacts
• Creates .aws-sam

Not deployment

Deploy

• Uploads to S3
• Creates CloudFormation stack
• Deploys AWS resources

Local Invoke

• Runs Lambda locally
• No deployment

Globals

• Shared Runtime
• Shared Timeout
• Shared Memory
• Reduces duplication
• Can be overridden

HttpApi Event

Automatically creates:

• HTTP API Gateway
• Route
• Integration
• Lambda permissions

10-Second Revision

• sam build → Prepare artifacts.
• sam deploy → Deploy using CloudFormation.
• sam local invoke → Test locally only.
• Globals → Shared defaults for all functions.
• HttpApi Event → Automatically creates an HTTP API Gateway and integrates it with Lambda.