Lambda (SAM)

This guide shows you how to work with AWS Lambda using the Serverless Application Model (SAM) and Python. This example demonstrates how to build and run a local API Gateway and Lambda service for direct SDK invocation.

Prerequisites

• Docker installed and running.
• SAM CLI installed.

Dev Containers

SAM CLI is not compatible with Dev Containers due to limitations when running inside a container.

How to execute

1. Setup Environment: Run the setup script to install tools and dependencies.

   scripts/setup.sh

2. Start Infrastructure: Launch both SAM local services (API Gateway and Lambda) in separate terminals.

   • API Gateway: to use HTTP requests or cURL:

     sam local start-api

   • Lambda SDK: to use the AWS SDK (boto3) or AWS CLI:

     sam local start-lambda

3. Run the Example:

   Python

   python main.py

   cURL

   curl "http://127.0.0.1:3000/get_secret?username=admin"

   REST Client
   1. Install REST Client VS Code extension.
   2. Open http/get_secret.http.
   3. Run Click on Send Request above the URL.
   AWS CLI
   1. Install AWS CLI.
   2. Run if you have AWS CLI installed globally:

      aws lambda invoke --function-name GetSecretFunction --profile sam --payload '{"queryStringParameters": {"username": "admin"}}' output.json

   3. Run if you have AWS CLI installed via mise:

      mise exec -- aws lambda invoke --function-name GetSecretFunction --profile sam --payload '{"queryStringParameters": {"username": "admin"}}' output.json

   4. Verify the output file output.json.

How to debug

Use the preconfigured VS Code debug profiles:

1. Python Script (main.py):

   • Ensure the local SAM services are running (sam local start-api and sam local start-lambda).
   • Run the Python: Main debug configuration.

2. Lambda Function:

   • Run the SAM: Debug get_secret debug configuration.

How to test

• All tests: Run the automated script:

  scripts/run_tests.sh

• Individually: Use the VS Code Testing tab to run or debug specific test cases.

Validate results

• Logs: Check the console output in the terminals where sam local is running to verify invocation details and log messages.
• AWS CLI Output: Verify that the generated output.json contains the expected HTTP response body and status code.

Clean Up

1. Stop the active SAM local services in your terminals.
2. Remove the virtual environment and uninstalled tools:

   rm -rf .venv
   mise uninstall -a

Next steps

• Build on this MVE with the Storage Writer project.
• Build on this MVE with the SQL Writer project.
• Build on this MVE with the Simple ETL project.