AWS Lambda – Simple Explanation with Example 

What is AWS Lambda?

AWS Lambda is a serverless compute service that lets you run code without managing servers.
You upload your code, and AWS automatically:

• Runs it

• Scales it

• Manages infrastructure

• Charges only for execution time

---

Simple Meaning

You write only the code. AWS handles servers, scaling, and availability.

---

🏗️ Traditional Server vs AWS Lambda

❌ Traditional Server

• Provision EC2

• Manage OS

• Handle scaling

• Pay even when idle

✅ AWS Lambda

• No servers to manage

• Auto-scaling

• Pay per request

• Event-driven

---

⚙️ How AWS Lambda Works

Event (HTTP / S3 / SQS / Cron)
          ↓
      AWS Lambda
          ↓
     Executes Code
          ↓
      Returns Result

---

🔔 What Can Trigger a Lambda?

Trigger	Use Case
API Gateway	REST APIs
S3	File upload processing
SQS	Message processing
SNS	Notifications
EventBridge	Scheduled jobs
DynamoDB	Stream processing

---

🧩 Supported Languages

• Python

• Java

• Node.js

• Go

• C#

• Ruby

---

🧪 Simple AWS Lambda Example (Python)

🎯 Use Case

Create a Lambda that returns “Hello from Lambda”

---

1️⃣ Lambda Function Code (Python)

def lambda_handler(event, context):
    return {
        "statusCode": 200,
        "body": "Hello from AWS Lambda!"
    }

---

2️⃣ Explanation

• event → input data (HTTP request, S3 event, etc.)

• context → runtime metadata

• Function returns response to the caller

---

3️⃣ Sample Input (API Gateway)

{
  "name": "Vinod"
}

---

4️⃣ Sample Output

{
  "statusCode": 200,
  "body": "Hello from AWS Lambda!"
}

---

Java Lambda Example (Very Simple)

public class HelloLambda {
    public String handleRequest() {
        return "Hello from Java Lambda";
    }
}

✔️ AWS invokes handleRequest()
✔️ No main method needed

---

AWS Lambda Pricing (High Level)

• Charged by:

  • Number of requests

  • Execution time (milliseconds)

• No cost when idle

📌 Free tier available (1M requests/month)

---

Key Benefits of AWS Lambda

• 🚀 Auto scaling

• 💸 Cost efficient

• 🛠️ No server management

• 🔄 Event-driven

• 🌍 High availability

---

Limitations (Interview Important)

Limitation	Details
Cold start	Initial startup delay
Execution time	Max 15 minutes
Stateless	No local persistence
Memory limits	Up to 10 GB

---

🌍 Real-World Use Cases

• REST APIs

• Image resizing

• File validation

• Background jobs

• Data transformation

• Event processing

---

AWS Lambda vs EC2 (Quick Compare)

Feature	Lambda	EC2
Server management	❌ No	✅ Yes
Scaling	Automatic	Manual
Pricing	Pay per execution	Pay per hour
Best for	Event-driven	Long-running apps

---

Interview One-Line Summary

AWS Lambda is a serverless compute service that runs code in response to events and automatically manages scaling and infrastructure.

---

Final Takeaways

• Lambda is event-driven

• Ideal for microservices

• No infrastructure management

• Best for short-lived tasks

• Backbone of serverless architecture