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Migrating a legacy API doesn’t have to mean rewriting everything from scratch.

In this video, I’ll show you how to apply the Strangler Fig Pattern in .NET to gradually migrate an existing API into a modern .NET 10 application.

We’ll start with a Node.js API backed by PostgreSQL, place a YARP reverse proxy in front of it, and then move endpoints one by one into a new .NET API. The old system keeps running the entire time, while the proxy decides which API should handle each request.

This is a practical approach you can use when migrating from legacy .NET Framework apps, older APIs, or even systems built with a different tech stack.

Topics covered:

- What the Strangler Fig Pattern is
- Why full rewrites are risky
- Adding YARP as a reverse proxy
- Routing traffic between old and new APIs
- Migrating endpoints one at a time
- Using response headers to verify routing
- Completing the migration safely

If you’re working with legacy systems and want a safer path to modern .NET, this pattern is worth knowing.

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Chapters

We Are .NET

A step-by-step walkthrough of applying the Strangler Fig pattern to migrate a Node.js/Express API to .NET 10 without a full rewrite. The approach uses YARP (Yet Another Reverse Proxy) as a traffic router placed in front of both the legacy and new APIs. Requests are incrementally rerouted endpoint by endpoint from the Node API to a new .NET 10 minimal API, using YARP route ordering and HTTP method matching. The demo uses PostgreSQL with Dapper and shows how to configure clusters, routes, and response header transforms in YARP. The same technique applies to migrating .NET Framework apps to .NET 10.

The Strangler Fig Pattern Explained With .NET 10