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Build Your First Serverless API on AWS: A Beginner's Guide to Lambda & API Gateway

Learn how to build a scalable, cost-effective serverless REST API using AWS Lambda, Amazon API Gateway, and Amazon DynamoDB. A perfect hands-on project to add to your developer resume and stand out to cloud recruiters.

Erick Rangel

Software Engineer | Data Engineering | AI Applications | Python | SQL | Cloud | Git | 42 Rio
Introduction
Every modern web or mobile application needs an API to communicate with a database. Traditionally, developers had to provision a server (like an EC2 instance), deploy their code, and keep it running 24/7. This meant paying for server uptime even when nobody was using the app.
As a student or junior software engineer, showing that you can build Serverless APIs is a massive advantage. It proves you know how to write code that scales automatically and costs zero dollars when idle. In this guide, we will build a basic "To-Do List" API entirely on the AWS Free Tier.

The Architecture Overview

We will build a fully decoupled, event-driven REST API using three core AWS services:
  • Amazon API Gateway: The "front door" that receives HTTP requests (GET, POST, etc.) from users.
  • AWS Lambda: The "brain" where your actual code (Python, Node.js, etc.) lives. It only runs when API Gateway triggers it.
  • Amazon DynamoDB: A fast, serverless NoSQL database to store our data.

How It Works

A simple serverless API flow looks like this:
User (Web/Mobile App) ↓ HTTP POST Request ↓ Amazon API Gateway (Receives and Routes Request) ↓ AWS Lambda (Executes Code) ↓ Amazon DynamoDB (Saves Data)

Step-by-Step Implementation

Step 1: Set Up the Database (Amazon DynamoDB)

First, we need a place to store our data.
  • Go to DynamoDB and create a new table called ToDoItems.
  • Set the Partition Key to id (String).
  • Leave all other settings as default and create the table. There are no servers to manage!

Step 2: Write the Business Logic (AWS Lambda)

Next, we write the code that will interact with our database.
  • Go to AWS Lambda and click Create function.
  • Name it CreateToDoItem and select your preferred language (like Python 3.10 or Node.js).
  • In the code editor, write a simple function that takes data from the event payload and saves it to your DynamoDB table.
  • Important: Make sure your Lambda Execution Role has permissions to write to DynamoDB!

Step 3: Create the Front Door (Amazon API Gateway)

Finally, we need to expose our Lambda function to the internet.
  • Go to API Gateway and build a REST API.
  • Create a new Resource called /todos.
  • Create a POST Method under this resource.
  • For the Integration Type, choose Lambda Function and select your CreateToDoItem function.
  • Deploy the API to a stage (e.g., dev). AWS will give you a public URL!

Why This Project Belongs on Your Resume

When you apply for Software Engineering or Backend Developer roles, hiring managers are looking for practical cloud skills. Building this project demonstrates that you understand:
  • Microservices Architecture: You know how to break down applications into small, independent services.
  • Event-Driven Computing: You understand that code should only run in response to specific triggers (like HTTP requests).
  • Cost Optimization (Pay-as-you-go): You know how to design systems that cost pennies per month compared to traditional always-on servers.
Final Thoughts: Moving from writing code on your local machine to deploying serverless architecture in the cloud is a huge milestone. Write the code → Expose it via an API → Store the data serverlessly. Deploy this project, push the code to your GitHub, and link the API endpoint in your portfolio! 🚀☁️
# software-engineering# aws-lambda# api-gateway
Any opinions in this article are those of the individual author and may not reflect the opinions of AWS.
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