🚀 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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