AWS Serverless Application Model (SAM)

AWS Serverless Application Model (SAM) is an open-source framework that simplifies building and deploying serverless applications on AWS.

It extends AWS CloudFormation, giving you a special, easier syntax for defining serverless resources like Lambda functions, API Gateways, and DynamoDB tables. SAM helps you manage your entire serverless app as a single unit.

At the core of every SAM application is the template.yaml file. This YAML (or JSON) file acts as the blueprint, describing all the serverless resources that make up your application.

SAM templates are essentially AWS CloudFormation templates, but they include a crucial Transform property that unlocks SAM's simplified, serverless-specific syntax.

Let's look at the key sections you'll find in a template.yaml file:

• AWSTemplateFormatVersion: Standard CloudFormation version.
• Transform: AWS::Serverless-2016-10-31: This is vital! It tells CloudFormation to use SAM's simplified syntax.
• Description: A short explanation of your application.
• Resources: This is where you define all your serverless components like Lambda functions, APIs, and databases.

In SAM, you define a Lambda function using the AWS::Serverless::Function resource type. You specify essential properties like its runtime, entry point (handler), memory, and how it gets triggered.

• Type: AWS::Serverless::Function: Identifies it as a Lambda.
• Handler: The function within your code that AWS Lambda calls to begin execution (e.g., app.lambda_handler).
• Runtime: The programming language environment (e.g., python3.9, nodejs16.x).
• CodeUri: The local path to your function's source code.
• Events: Specifies how your function is invoked (e.g., an API Gateway endpoint).

Here's a simple Python Lambda function. It will be the code executed when our serverless function is invoked. It just returns a 'Hello from Lambda!' message.

Now, let's define our 'Hello World' Lambda function in a template.yaml. We'll set it up to be triggered by an API Gateway GET request at the /hello path.

This template assumes your Python code (app.py) is in a folder named hello_world/ next to this template.yaml file.

The AWS SAM Command Line Interface (CLI) is your main tool for developing and deploying SAM applications. It provides commands to initialize projects, build dependencies, test locally, and deploy your application to AWS.

• sam init: Start a new serverless project.
• sam build: Package your application code and dependencies.
• sam deploy: Deploy your application to AWS CloudFormation.

Before you can deploy your application, you need to 'build' it. The sam build command collects your code, bundles any dependencies (like Python packages), and prepares everything into a deployable package.

This command creates a .aws-sam directory containing the processed artifacts.

Once built, use sam deploy to push your application to AWS. This command creates or updates a CloudFormation stack based on your SAM template, provisioning all the necessary resources.

You'll need to specify a unique stack name and an S3 bucket for code artifacts. The --capabilities CAPABILITY_IAM argument acknowledges that your template creates IAM roles.

You've just learned the fundamentals of AWS SAM!

• SAM simplifies serverless application development and deployment using a CloudFormation-based template.
• Key components include the template.yaml with its Transform property and Resources section.
• The SAM CLI provides commands like sam init, sam build, and sam deploy to manage your applications.

With SAM, you can efficiently define, build, and deploy complex serverless architectures, making it a powerful tool for serverless development.