"Big Bang" rewrites fail 70% of the time. They are expensive, risky, and pause business features. The Strangler Fig Pattern offers a safer route: replacing the system piece by piece while it runs.
What is Strangler Fig?
Named after a tree that grows around a host tree and eventually replaces it, this software pattern involves placing an API Gateway (like Azure APIM or AWS API Gateway) in front of your legacy .NET Framework app.
The Process
- Intercept: Route all traffic through the Gateway. Initially, 100% of traffic goes to the Legacy App.
- Isolate: Identify one module (e.g., "User Profile") to rewrite.
- Rewrite: Build a new Microservice (e.g., in .NET 8) for just "User Profile".
- Route: Update the Gateway to send `/api/users` traffic to the new service, while everything else still goes to Legacy.
- Repeat: Continue until the Legacy App is handling 0% of traffic, then decommission it.
Key Insight: This decouples "Modernization" from "Business Logic". You can
release new features in the new stack from Day 1.