Migrating a Legacy Monolith to Serverless on AWS

Source: Dev.to

Overview

This project demonstrates how to migrate a legacy monolithic application to a serverless architecture using the Strangler Fig Pattern on AWS, leveraging:

• Terraform for Infrastructure as Code
• Python for application logic

The goal is to show how new features can be carved out from a monolith and replaced with serverless components—without breaking the existing system.

Architecture

The solution consists of the following major components:

• Legacy Monolith
• New Serverless Components

Route Behavior

Prerequisites

Before deploying, ensure you have:

• An AWS account (Free Tier eligible)
• AWS CLI installed & configured (aws configure)
• Terraform v1.0+
• Postman or curl for testing

Project Structure

strangler-fig-aws-migration-demo/

Deployment Instructions

1️⃣ Initialize Terraform

# Inside the infra-terraform directory
terraform init

2️⃣ Deploy Infrastructure

terraform apply

Type yes when prompted.
Deployment takes ~2 minutes, plus an additional ~3 minutes for the EC2 instance to install dependencies and start the legacy server.

3️⃣ Retrieve the API URL

Terraform will output a value similar to:

api_url = "https://.execute-api.us-east-1.amazonaws.com"

Copy this URL for testing.

Testing Scenarios

Example request for Scenario 3:

curl -X POST /products/restock

Troubleshooting Guide

Re‑run the request if needed:

curl -X POST /products/restock

Cleanup (To Avoid Charges)

When finished, destroy all resources:

terraform destroy