Timeline: 2024/2025 · Category: 💼 Professional

Throughout 2024/2025, I migrated several core utility applications from .NET Framework 4.x to .NET 9. This modernization was a critical step to bring legacy systems that had grown over the years up to the current state of technology and prepare them for upcoming versions like .NET 10.

The Starting Point

The affected applications had been running stably on .NET Framework 4.x for years. However, maintenance was becoming increasingly complex:

  • Outdated Libraries: Many dependencies were no longer receiving updates.
  • Security: Difficulties integrating current security patches.
  • Technology Gap: The team wanted to leverage the benefits of modern C# and new .NET features.

The challenge was a smooth transition during ongoing operations.

What I Did

Analysis & Planning

  • Dependency Check: Verification of all NuGet packages for compatibility with .NET 9.
  • Risk Minimization: Creation of a migration plan to minimize impact on production.

Technical Implementation

  • Project Modernization: Conversion to the new SDK-style format.
  • Code Adaptation: Replacing deprecated APIs with modern equivalents and resolving version conflicts.
  • Architecture Upgrade: Implementation of Dependency Injection and the modern Options Pattern (appsettings.json) to make the code cleaner and more maintainable.

Rollout & Quality Assurance

  • Staged Deployment: Execution of stable rollouts across the environments DEV → QA → PROD.
  • Validation: Execution of regression tests in each phase to ensure that existing business logic continues to function flawlessly.

Results

  • 🚀 Higher Performance: Significantly faster build times and optimized runtime performance.
  • 🛠️ Better Maintainability: Through modern patterns, the code is much easier to read and extend.
  • 🔮 Ready for .NET 10: The applications are now structured so that future updates to .NET 10 are possible with minimal effort.

Tech Stack

C# · .NET 9 · ASP.NET Core · SQL Server · Azure DevOps · Git