Serverless Applications with AWS Lambda & API Gateway

Introduction

Building and running servers manually is becoming a thing of the past. Developers today want to focus on code — not on provisioning, scaling, or managing infrastructure. That’s exactly what serverless computing offers. With AWS Lambda and API Gateway, you can build and deploy full-featured backends that scale automatically and only charge you for actual usage. In this post, you’ll learn how serverless architecture works, how Lambda and API Gateway fit together, and how to create a simple serverless API from scratch.

What Is Serverless Computing?

Serverless doesn’t mean there are no servers — it means you don’t have to manage them. AWS handles provisioning, scaling, and maintenance automatically. You just deploy small functions that run when triggered.

Benefits of Serverless

No server management: AWS handles all infrastructure.
Automatic scaling: Functions scale based on demand.
Cost efficiency: You pay only when functions run.
Fast development: Ideal for APIs, automation, and event processing.

Serverless is perfect for modern cloud-native applications where flexibility and cost control matter most.

AWS Lambda Overview

AWS Lambda lets you run code in response to events — like an API call, file upload, or database update. You write your logic as a function, and AWS executes it automatically when triggered.

Example Function (Python)

def handler(event, context):
    name = event.get('name', 'Guest')
    return {"statusCode": 200, "body": f"Hello, {name}!"}

You can write functions in multiple languages including Python, Node.js, Go, and Java. Lambda automatically manages scaling and concurrency behind the scenes.

Key Concepts

Handler: The entry point of your code.
Trigger: The event source (e.g., API Gateway, S3, DynamoDB).
Execution Role: IAM role defining what resources the function can access.
Timeout: The maximum runtime for a single execution.

AWS API Gateway Overview

API Gateway acts as the front door to your Lambda functions. It receives HTTP requests, processes them, and triggers your function accordingly.

Key Features

REST and WebSocket APIs: Build both traditional and real-time APIs.
Request validation and transformation: Filter and modify inputs.
Rate limiting and throttling: Protect your backend.
Authentication: Supports IAM, Cognito, and custom authorizers.

API Gateway integrates seamlessly with Lambda, enabling you to build scalable APIs without setting up servers.

Building a Serverless API with Lambda and API Gateway

Create a Lambda Function:
- Go to the AWS Lambda console.
- Click Create function → Author from scratch.
- Choose a runtime (Python, Node.js, etc.) and an IAM role with necessary permissions.
Write Your Code:
Add your handler logic in the inline editor or upload it from your local project.
Create an API Gateway:
- Open Amazon API Gateway.
- Choose Create API → REST API.
- Create a new resource and method (e.g., /hello with GET).
- Link it to your Lambda function.
Deploy the API:
Click Deploy API, choose a stage (e.g., “dev”), and copy the endpoint URL.
Test It:
Visit the endpoint in your browser — you should see your Lambda response.

Congratulations! You’ve deployed your first serverless API.

Managing and Monitoring Serverless Apps

Use AWS CloudWatch to monitor execution metrics like duration, memory, and errors. You can also set alerts for failed executions or high latency. For logging, CloudWatch automatically captures Lambda logs so you can debug easily.

Best Practices

Keep functions small and focused.
Reuse connections to databases (don’t open new ones per request).
Set timeouts and memory based on actual workloads.
Secure APIs using authentication and throttling.
Use environment variables to manage configurations.

When to Use Serverless

Serverless shines in scenarios where workloads are event-driven, unpredictable, or infrequent:

APIs and microservices
Scheduled jobs and automation
File processing (e.g., image resizing, report generation)
Chatbots and IoT backends

However, it’s less ideal for long-running processes or workloads needing full control over the infrastructure.

Final Thoughts

AWS Lambda and API Gateway make building serverless applications incredibly simple. You can deploy production-ready APIs without maintaining a single server — reducing costs, increasing scalability, and speeding up development. Start with one function, connect it through API Gateway, and scale from there. To continue your cloud journey, check out Kubernetes 101: Deploying and Managing Containerised Apps. For official resources, see the AWS Lambda documentation.