AWS Lambda: Serverless Computing Guide

What is AWS Lambda?

AWS Lambda is a serverless compute service that lets you run code without provisioning or managing servers. You pay only for the compute time you consume.

How Lambda Works

Function Structure

import { APIGatewayProxyEvent, APIGatewayProxyResult } from 'aws-lambda';

export const handler = async (
    event: APIGatewayProxyEvent
): Promise<APIGatewayProxyResult> => {
    const { name } = JSON.parse(event.body || '{}');

    return {
        statusCode: 200,
        body: JSON.stringify({
            message: `Hello, ${name}!`,
        }),
    };
};

Execution Model

1. Lambda receives an event trigger
2. A new execution environment is created (cold start) or reused (warm start)
3. Your function code executes
4. Lambda returns the response

Common Triggers

• API Gateway - REST/HTTP APIs
• S3 - File upload processing
• DynamoDB Streams - Database change events
• SQS - Message queue processing
• CloudWatch Events - Scheduled tasks

Best Practices

Minimize Cold Starts

// Initialize outside handler for connection reuse
import { DynamoDB } from '@aws-sdk/client-dynamodb';

const dynamodb = new DynamoDB({});

export const handler = async (event: any) => {
    // Use the pre-initialized client
    const result = await dynamodb.getItem({
        TableName: 'users',
        Key: { id: { S: event.userId } },
    });
    return result.Item;
};

Environment Variables

Use environment variables for configuration instead of hardcoding values:

# serverless.yml
functions:
    processOrder:
        handler: src/handlers/order.handler
        environment:
            TABLE_NAME: ${self:custom.tableName}
            REGION: ${aws:region}

Pricing

Resource	Free Tier	Cost After
Requests	1M/month	$0.20 per 1M
Duration	400K GB-s	$0.0000166667/GB-s
Memory	128MB-10GB	Included

Conclusion

AWS Lambda is a powerful tool for building scalable, event-driven applications. Understanding its execution model and following best practices will help you build efficient serverless architectures.