[tutorial] Using AWS SAM to Create and Run Lambda Functions

Note: This page is an AI-generated (gpt-5-mini-2025-08-07) translation from Traditional Chinese and may contain minor inaccuracies.

📌 Introduction

This guide explains how to use AWS SAM to create and run Lambda functions, including basic installation, project structure explanation, and the workflow for running Lambdas locally

🚀 Quick Start

AWS CLI

brew install awscli

AWS SAM (Serverless Application Model) CLI

brew install aws-sam-cli

Initialize SAM project

sam init

Project structure overview

.
├── __init__.py
├── events
│   └── event.json
├── hello_world
│   ├── __init__.py
│   ├── app.py
│   └── requirements.txt
├── README.md
├── samconfig.toml
├── template.yaml
└── tests
    ├── __init__.py
    ├── integration
    │   ├── __init__.py
    │   └── test_api_gateway.py
    ├── requirements.txt
    └── unit
        ├── __init__.py
        └── test_handler.py

• events/ - Directory for JSON files containing mock events (event payloads) used to test Lambda functions
• hello_world/ - Where the application is placed; Lambda-related functions including the handler (e.g., app.py) and dependencies (e.g., requirements.txt)
• tests/ - Folder for unit tests
• samconfig.toml - Stores SAM CLI execution parameters (e.g., deployment region, Stack name, S3 bucket) to simplify configuration when running sam deploy
• template.yaml - Defines all Lambda functions; the main IaC core file (which services are used and their dependencies); it’s an extension of AWS CloudFormation syntax

template.yaml

You can use the CloudFormation Linter tool cfn-lint to detect formatting and property errors in the file

Header

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  TODO....

1. AWSTemplateFormatVersion - The version number of AWS CloudFormation
2. Transform - Tells CloudFormation that this template uses SAM to extend the syntax
3. Description - Project description

Content

1. Globals - Default settings provided to Resources
2. Resources - AWS resources to create; refer to AWS resource and property types reference, AWS SAM resources and properties
3. Outputs - Expected outputs after deployment (the information you need to know)

samconfig.toml

See AWS SAM CLI configuration file, Configuring the AWS SAM CLI, AWS SAM CLI command reference

The purpose is to simplify the complexity when using sam commands

Original	Optimized with samconfig
sam build --cached --parallel --use-containers	sam build
sam local invoke --env-vars locals.json	sam local invoke
sam local start-api --env-vars locals.json --warm-containers EAGER	sam local start-api

Local Invoke

sam local invoke

No current session found, using default AWS::AccountId                                                       
Invoking app.lambda_handler (python3.13)                                                                    
Local image is up-to-date                                                                                   
Using local image: public.ecr.aws/lambda/python:3.13-rapid-x86_64.                                           
                                                                                                            
Mounting /Users/XXXXXX/Documents/TEST/hello_world as 
/var/task:ro,delegated, inside runtime container                                                            
START RequestId: f6a6ec50-58b2-432c-9381-ec45ca43b130 Version: $LATEST
END RequestId: e883464b-1216-43ae-b0fe-f7f803a73057
REPORT RequestId: e883464b-1216-43ae-b0fe-f7f803a73057  Init Duration: 1.26 ms  Duration: 381.91 ms     Billed Duration: 382 ms     Memory Size: 128 MB     Max Memory Used: 128 MB
{"statusCode": 200, "body": "{\"message\": \"hello world\"}"}

🔁 Recap

• Installation commands
• Understand the AWS SAM project structure
• Know the purpose of specific files template.yaml and samconfig.toml and their official documentation for fields
• Invoke a simple Hello World Lambda function locally

🔗 References

• Day02 - Environment Setup (1): Install AWS CLI, Docker, AWS SAM CLI