🚀 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 major components:

Legacy Monolith Python Flask app running on an EC2 instance.

New Serverless Components AWS Lambda functions,DynamoDB tables,API Gateway (The Strangler Facade) Routes traffic to the appropriate backend (legacy or new).

🔎 Route Behavior `/users → Legacy Route Proxies traffic to EC2 running the Flask app.

/products → Migrated Route Handled by Lambda + DynamoDB.

/products/restock → Enhanced Route POST request that simulates a failure 60% of the time to demonstrate resiliency handling.`

🖼 Architecture Diagram

📦 Prerequisites

Before deploying, ensure you have:

• 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/ │ ├── README.md ├── infra-terraform/ │ ├── provider.tf │ ├── variables.tf │ ├── ec2.tf │ ├── dynamodb.tf │ ├── lambda.tf │ ├── apigateway.tf │ ├── outputs.tf │ ├── lambda_function/ │ │ └── lambda_function.py │ └── legacy_app/ │ └── legacy_server.py

🚀 Deployment Instructions

1️⃣ Initialize Terraform

Inside infra-terraform:

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 something like:

api_url = "https://<random-id>.execute-api.us-east-1.amazonaws.com" Copy this value for testing.

🔬 Testing Scenarios

Scenario 1: Legacy Route (/users) Traffic routed to EC2 Flask app.

Scenario 2: Migrated Route (/products) Traffic routed to Lambda + DynamoDB.

Scenario 3: Chaos Route (/products/restock) A POST endpoint simulating 60% failure rate.

Request:

curl -X POST <api_url>/products/restock

Expected Behavior:

Chance Response 40% 200 OK → {"status": "Restock Successful"} 60% 500 Internal Server Error → Simulated external failure

🛠 Troubleshooting Guide

❌ 1. 502 Bad Gateway

Cause: API Gateway couldn’t reach EC2 instance. Fix: Wait 2–3 minutes after deployment Ensure EC2 is running Re-run terraform apply

❌ 2. 400 Bad Request

Cause: Payload version mismatch. Fix: Ensure this is inside your Lambda integration block: payload_format_version = "2.0"

❌ 3. 500 Internal Server Error

Cause: Expected behavior for chaos testing. Fix: Run the command multiple times or remove the failure logic in lambda_function.py.

❌ 4. 405 Method Not Allowed

Cause: Using GET on a POST-only route. Fix: Use the correct method: curl -X POST <api_url>/products/restock 🧹 Cleanup (To Avoid Charges)

When finished, destroy all resources:

terraform destroy Double-check the AWS Console to ensure everything is deleted.

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