SAM CLI: Serverless Made Simple (or million lines terraform?)

Still deploying Lambda functions by hand?

We’ve all been there: manually zipping code, uploading to S3, configuring triggers, setting up API Gateway… it’s enough to make you question if serverless is actually worth it. Or worse, writing hundreds of lines of Terraform just to deploy a simple function.

Enter AWS SAM CLI

AWS Serverless Application Model (SAM) CLI cuts through all of that. Think of it as Docker Compose for Lambda functions.

# Install it
brew install aws-sam-cli

The 30-second serverless app

Create a new project:

sam init

Choose the “Hello World Example” with Python, and you’ll get a project structure like this:

my-app/
├── hello_world/
│   ├── __init__.py
│   ├── app.py
│   └── requirements.txt
├── events/
│   └── event.json
├── template.yaml
└── tests/

template.yaml is where your entire application lives:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  HelloWorldFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: hello_world/
      Handler: app.lambda_handler
      Runtime: python3.9
      Events:
        HelloWorld:
          Type: Api
          Properties:
            Path: /hello
            Method: get

Test locally (yes, really!)

sam local invoke

Or start a local API (Requires docker):

sam local start-api

Deploy with a single command

sam deploy --guided

One command builds your code, packages it, creates or updates the CloudFormation stack, and hands you an API endpoint.

Pro tip: Use SAM Accelerate for faster iterations

sam sync --watch

This watches for file changes and syncs them to the cloud automatically. No full redeployment needed.