🚀 What is Serverless? Serverless vs Monolith Explained with AWS Lambda

Learn how serverless architectures differ from traditional monoliths—and get hands-on with AWS Lambda in Node.js.

📍 Introduction

For decades, most web applications were built as monoliths: one big codebase running on servers you managed yourself.
Now, serverless is all the rage—where you write functions, upload them, and let the cloud handle everything else.

In this post, you’ll discover:

1. What a monolithic architecture looks like

2. What serverless really means

3. Key differences between them

4. A practical AWS Lambda example in Node.js

5. When to choose serverless over monolith (and vice versa)

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🏗️ 1. Monolith Architecture

Definition

A monolith combines all features—UI, business logic, data access—into a single deployable unit.

Typical Stack

• One codebase (e.g., Express app)

• One database (e.g., MongoDB)

• Deployed on VMs or containers (EC2, Docker)

Pros & Cons

☁️ 2. What is Serverless?

Definition

Serverless means you write small, single-purpose functions, deploy them, and the provider auto-scales & manages the servers.

Characteristics

• Event-driven: e.g., HTTP requests, queue messages

• Pay-per-use: billed per invocation & duration

• Auto-scaling: scales down to zero when idle

⚔️ 3. Monolith vs Serverless Comparison

🛠️ 4. Hands-On: Building an AWS Lambda Function in Node.js

Prerequisites

• AWS CLI configured

• Node.js (v14+)

• SAM CLI (optional)

1. Initialize

mkdir lambda-hello
cd lambda-hello
npm init -y
npm install aws-sdk

2. Write Your Function (index.js)

exports.handler = async (event) => {
  console.log("Event:", event);
  return {
    statusCode: 200,
    body: JSON.stringify({ message: "Hello from AWS Lambda!" })
  };
};

3. Deploy with AWS CLI

zip -r function.zip .
aws lambda create-function \
  --function-name helloServerless \
  --runtime nodejs14.x \
  --handler index.handler \
  --zip-file fileb://function.zip \
  --role arn:aws:iam::<YOUR_ACCOUNT_ID>:role/<YOUR_LAMBDA_ROLE>

4. Test It

aws lambda invoke \
  --function-name helloServerless \
  --payload '{}' response.json
cat response.json

🎯 5. When to Use Serverless vs Monolith Choose Monolith when:

• Choose Monolith when:

  • You need low-latency, always-on services

  • You have complex interdependent modules

  • You prefer simple deployments

• Choose Serverless when:

  • You build event-driven microservices

  • You want zero-ops for scaling

  • You have unpredictable or spiky traffic

🔑 Key Takeaways

• Monolith = one big deployable, full control, but harder to scale per feature

• Serverless = functions-as-a-service, auto-scale, pay-per-use, but watch out for cold starts

• AWS Lambda makes it easy to get started—just write your code, upload, and call