What is AWS SAM (Serverless Application Model)?

AWS SAM (Serverless Application Model) is an open-source framework for building serverless applications on Amazon Web Services (AWS). It extends AWS CloudFormation to provide a simplified way of defining the Amazon API Gateway APIs, AWS Lambda functions, and Amazon DynamoDB tables needed by your serverless application. SAM uses a simple YAML syntax to define the resources and their properties, making it easier to manage and deploy serverless applications.

Here is a technical breakdown of the key components and concepts in AWS SAM:

  1. AWS SAM Template:
    • The core of AWS SAM is the template file written in YAML. This template describes the AWS resources that make up your serverless application.
    • The SAM template includes sections for defining:
      • AWS Serverless functions (AWS Lambda functions).
      • Event sources triggering the functions (e.g., API Gateway, S3, DynamoDB).
      • Resources such as API Gateway APIs and DynamoDB tables.
      • Permissions and policies associated with the functions and resources.
  2. AWS SAM CLI (Command Line Interface):
    • The AWS SAM CLI is a set of command-line tools for local development and deployment of serverless applications.
    • It allows developers to:
      • Test functions locally in a Lambda-like environment using sam local invoke.
      • Start a local API Gateway for testing API functionality using sam local start-api.
      • Package and deploy serverless applications to AWS using sam deploy.
  3. AWS Serverless Functions (Lambda):
    • SAM simplifies the definition of Lambda functions in the template.
    • Developers can specify the runtime, handler function, environment variables, and other configurations directly in the SAM template.
  4. Event Sources:
    • SAM enables the definition of event sources that trigger Lambda functions.
    • Common event sources include API Gateway, S3, DynamoDB, SNS, and more.
    • Event sources are defined in the SAM template, establishing the connections between different parts of the serverless application.
  5. Resource Policies:
    • SAM allows you to define resource policies, which are IAM policies associated with AWS resources.
    • For example, you can specify permissions for Lambda functions to access specific DynamoDB tables or allow API Gateway to invoke Lambda functions.
  6. AWS CloudFormation Integration:
    • SAM templates are an extension of AWS CloudFormation templates.
    • SAM transforms SAM templates into standard CloudFormation templates, allowing them to be deployed using standard CloudFormation commands.
    • This integration ensures compatibility with existing CloudFormation features and workflows.
  7. Local Testing and Debugging:
    • SAM CLI provides local testing and debugging capabilities, allowing developers to iterate quickly during the development phase.
    • This helps identify and fix issues before deploying the serverless application to AWS.
  8. Lambda Layers and Globals:
    • SAM supports features like Lambda Layers and Globals to manage shared code and configurations across multiple functions.

AWS SAM simplifies the development and deployment of serverless applications on AWS by providing a higher-level abstraction with a YAML-based template, facilitating local testing, and integrating seamlessly with AWS CloudFormation for deployment and management.