Serverless Application Model (SAM) in AWS - Commands & Configuration

Introduction

Building serverless applications can be complex because you need to manage many resources like functions, APIs, and databases. AWS Serverless Application Model (SAM) helps by letting you define all these resources in a simple file, so you can deploy and manage your app easily.

When you want to create a simple API using AWS Lambda and API Gateway without managing servers.

When you need to deploy a function that reacts to events like file uploads or database changes.

When you want to package and deploy your serverless app as one unit instead of separate pieces.

When you want to test your serverless functions locally before deploying to the cloud.

When you want to automate deployment of serverless apps using a single configuration file.

Config File - template.yaml

template.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: Simple SAM app with one Lambda function and API Gateway
Resources:
  HelloWorldFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: app.lambda_handler
      Runtime: python3.9
      CodeUri: ./src/
      Events:
        HelloWorldApi:
          Type: Api
          Properties:
            Path: /hello
            Method: get

This file defines a serverless app with one Lambda function called HelloWorldFunction. The Transform line tells AWS this is a SAM template. The function uses Python 3.9 and runs code from the src folder. It is triggered by an HTTP GET request to the /hello path via API Gateway.

Commands

This command processes your SAM template and prepares your application for deployment by installing dependencies and packaging your code.

Terminal

sam build

Expected Output

Building codeuri: ./src runtime: python3.9 metadata: {} architecture: x86_64 functions: ['HelloWorldFunction']

Running PythonPipBuilder

Build Succeeded

This command deploys your serverless app to AWS. The --guided flag walks you through configuration options like region and permissions, and saves them for future deploys.

Terminal

sam deploy --stack-name my-sam-app --guided

Expected Output

Configuring SAM deploy

Stack Name [my-sam-app]: 

AWS Region [us-east-1]: 

Confirm changes before deploy [y/N]: N

Allow SAM CLI IAM role creation [Y/n]: Y

Save arguments to samconfig.toml [Y/n]: Y



Deploying with following values

===============================

Stack name                 : my-sam-app

Region                     : us-east-1

Confirm changeset          : false

Deployment s3 bucket       : sam-deployments-bucket

Capabilities               : CAPABILITY_IAM



Waiting for stack create/update to complete

Successfully created/updated stack - my-sam-app

→

--stack-name - Names the CloudFormation stack for your app

→

--guided - Runs interactive setup for deployment options

This command lists all AWS resources created by your deployed SAM app, so you can verify what is running.

Terminal

sam list resources --stack-name my-sam-app

Expected Output

Name                      Type                          LogicalId

HelloWorldFunctionRole     AWS::IAM::Role                HelloWorldFunctionRole

HelloWorldFunction        AWS::Lambda::Function          HelloWorldFunction

HelloWorldApi             AWS::ApiGateway::RestApi       HelloWorldApi

→

--stack-name - Specifies which deployed app's resources to list

This command shows the live logs from your Lambda function, helping you see what happens when it runs.

Terminal

sam logs -n HelloWorldFunction --stack-name my-sam-app --tail

Expected Output

START RequestId: 1234abcd-5678-efgh-9012-ijklmnopqrst Version: $LATEST

2024-06-01T12:00:00.000Z	1234abcd-5678-efgh-9012-ijklmnopqrst	Hello from Lambda!

END RequestId: 1234abcd-5678-efgh-9012-ijklmnopqrst

REPORT RequestId: 1234abcd-5678-efgh-9012-ijklmnopqrst Duration: 3 ms Billed Duration: 100 ms Memory Size: 128 MB Max Memory Used: 45 MB

→

-n - Specifies the function name to get logs for

→

--tail - Streams logs live as they come

Key Concept

If you remember nothing else from SAM, remember: it lets you define and deploy your serverless app with one simple file and easy commands.

Common Mistakes

Not running 'sam build' before 'sam deploy'

Your code and dependencies won't be packaged correctly, causing deployment errors or broken functions.

Always run 'sam build' first to prepare your app before deploying.

Forgetting to specify the stack name during deployment

SAM won't know which CloudFormation stack to update, causing deployment to fail or create unexpected stacks.

Use the --stack-name flag with a clear name every time you deploy.

Not checking logs after deployment

You miss errors or issues in your function that only appear when it runs in AWS.

Use 'sam logs' to view function output and troubleshoot.

Summary

Use a template.yaml file to define your serverless functions and triggers.

Run 'sam build' to prepare your app, then 'sam deploy --guided' to send it to AWS.

Check your deployed resources with 'sam list resources' and troubleshoot with 'sam logs'.