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The Case: An insurance company with a 15-year-old ASP.NET WebForms application that is impossible to maintain and won't run in modern browsers.
We didn't try to rewrite the whole app. We created a new **Blazor Server** project and hosted it under a sub-path (e.g., /modern). We shared the Authentication Cookie between the old WebForms app and the new Blazor app, so the user could switch between them without logging in again.
We identified the most 'painful' pages in WebForms and rebuilt them as Blazor components. Because both use C#, we were able to copy-paste much of the business logic and data access code with only minor adjustments. We used a **Razor Class Library** to hold these new components so they could be reused in both the interim 'Side-by-Side' app and the final full Blazor app.
After 12 months, the entire app was migrated. The page size dropped by 70%, the server load dropped by 50%, and the developers are now building features 3x faster using modern C# 12 and .NET 8 features. The 'Legacy' tag is finally gone.
Q: "Why choose Blazor over React for this migration?"
Architect Answer: "Lower risk. The team already knew C#. Rewriting in React would have required hiring new people or retraining everyone in JS/TypeScript/React. With Blazor, they were productive in week one. Architecture is always about balancing technical perfection with business reality and team skills."
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On this page
1. Step 1: The 'Side-by-Side' Strategy 2. Step 2: Componentization 3. The Final Result 3. Architect Insight