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Building My First Serverless REST API with Lambda and API Gateway

Building My First Serverless REST API with Lambda and API Gateway

After learning Lambda, I wanted to build something real. In this article, I share how I connected AWS Lambda to API Gateway, created a simple REST API endpoint, tested it with a browser and curl, and what I learned about serverless backends. Based on official AWS documentation.

Introduction

In my previous article, I built my first AWS Lambda function and connected it to an S3 trigger. That was exciting, but I wanted to go further. I wanted to build something that could respond to HTTP requests — like a real API.
That's when I learned about Amazon API Gateway.
AWS documentation describes API Gateway as a fully managed service that makes it easy for developers to create, publish, maintain, monitor, and secure APIs at any scale. When combined with Lambda, it lets you build a serverless backend without managing any servers.
In this article, I'll share how I built my first serverless REST API using Lambda and API Gateway. Everything here is based on the official AWS documentation.

What Is API Gateway?

Before building, I read the documentation. Here is what I understood:
  • API Gateway acts as the "front door" for your application. It receives HTTP requests and routes them to the right backend.
  • It works with Lambda to create a fully serverless API. No servers to manage.
  • It handles authentication, throttling, and monitoring so you don't have to build those from scratch.
  • It supports REST APIs, HTTP APIs, and WebSocket APIs. For beginners, HTTP APIs are simpler and cheaper.
The AWS Free Tier includes 1 million API calls per month for the first 12 months, which is more than enough for learning.

Step 1: Create a Lambda Function for the API

First, I created a new Lambda function that would handle API requests.
  1. Open the AWS Lambda console.
  2. Choose Create function.
  3. Choose Author from scratch.
  4. Enter a Function name (for example, my-first-api-function).
  5. For Runtime, choose Python 3.12.
  6. Keep the default permissions and choose Create function.
Then I replaced the default code with this simple handler:
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import json

def lambda_handler(event, context):
name = "World"

if 'queryStringParameters' in event and event['queryStringParameters']:
if 'name' in event['queryStringParameters']:
name = event['queryStringParameters']['name']

return {
'statusCode': 200,
'headers': {
'Content-Type': 'application/json'
},
'body': json.dumps({
'message': f'Hello, {name}!',
'source': 'Lambda + API Gateway'
})
}
This function reads a name parameter from the query string and returns a greeting. If no name is provided, it defaults to "World".
I saved the function and moved on to API Gateway.

Step 2: Create an HTTP API in API Gateway

Next, I created the API that would trigger my Lambda function.
  1. Open the API Gateway console.
  2. Choose Create API.
  3. Under HTTP API, choose Build.
  4. For API name, enter my-first-api.
  5. Choose Next.
  6. Under Configure routes, choose Add integration → Lambda.
  7. Select your Lambda function (my-first-api-function).
  8. For Method, choose GET.
  9. For Resource path, enter /hello.
  10. Choose Next.
  11. For Stage name, keep $default.
  12. Choose Create.
API Gateway automatically created a route and gave me an Invoke URL. It looked something like this:
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https://abc123xyz.execute-api.us-east-1.amazonaws.com/hello

Step 3: Test the API

I opened a browser and pasted the Invoke URL. The response was:
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{
"message": "Hello, World!",
"source": "Lambda + API Gateway"
}
It worked! My serverless API was live.
Then I tested it with a query parameter by adding ?name=Aman to the URL:
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https://abc123xyz.execute-api.us-east-1.amazonaws.com/hello?name=Aman
The response was:
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{
"message": "Hello, Aman!",
"source": "Lambda + API Gateway"
}
I also tested it using curl in my terminal:
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curl "https://abc123xyz.execute-api.us-east-1.amazonaws.com/hello?name=Aman"
The same result came back. My API was working from both the browser and the command line.

Step 4: Understanding the Flow

Here is what happens when someone calls the API:
  1. A user sends a request to the API Gateway URL.
  2. API Gateway receives the request and routes it to the Lambda function.
  3. Lambda runs the code and returns a response.
  4. API Gateway sends the response back to the user.
This is the core of serverless architecture. No servers, no infrastructure management, and you only pay for what you use.

Step 5: Clean Up

After testing, I deleted the resources to avoid unexpected charges.
  1. Open the API Gateway console.
  2. Select your API.
  3. Choose Actions → Delete.
  4. Confirm.
Then I deleted the Lambda function:
  1. Open the Lambda console.
  2. Select your function.
  3. Choose Actions → Delete.
  4. Confirm.
AWS documentation recommends cleaning up resources after testing.

What I Learned

Building my first serverless API taught me three things:
  1. API Gateway + Lambda is powerful. You can build a real API without managing any servers.
  2. Query parameters are easy to handle. The event object in Lambda contains everything you need.
  3. Serverless is cost-effective. With the Free Tier, 1 million API calls and 1 million Lambda requests per month are more than enough for learning.

What's Next for Me

My next step is to connect this API to a DynamoDB table so I can store and retrieve data. This will help me understand how to build a complete serverless CRUD application.

Let's Discuss

  • Have you built an API with Lambda and API Gateway?
  • Did you use REST API or HTTP API?
  • What was the hardest part of learning API Gateway?
Let's learn together. ☁️⚡
# amazon-api-gateway# aws-lambda# serverless# rest-api# beginner-projects
Any opinions in this article are those of the individual author and may not reflect the opinions of AWS.
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