The Challenge
When I joined the EUCARIS modernization project, we were staring at a legacy .NET Framework system that had been serving European countries for years. It worked—but it was showing its age. The framework was approaching end-of-life, security patches were getting harder to maintain, and the monolithic architecture made every change a delicate operation.
As a team, we knew we needed to migrate to .NET 8, but this wasn't just a lift-and-shift. EUCARIS handles cross-border vehicle data exchange across multiple European countries. Any downtime or data loss could impact law enforcement, customs, and registration authorities across borders.
The Journey Begins
We started by mapping out dependencies and understanding which parts of the system could be modularized. The old codebase had grown organically over years, with business logic intertwined with data access and UI concerns. Our first major decision was to introduce clean architecture principles—separating concerns into layers that could be tested and maintained independently.
Choosing Blazor for the frontend was both exciting and nerve-wracking. Moving from traditional server-side rendering to a modern SPA framework meant retraining the team and rethinking how we approached UI development. But Blazor's component model and C# throughout the stack meant we could leverage our existing skills while modernizing the user experience.
Testing: The Foundation of Confidence
One of the biggest lessons from this migration was the value of comprehensive testing. We couldn't afford to break existing functionality during the transition. We established a testing strategy using xUnit for unit tests, integration tests for API endpoints, and Playwright for end-to-end UI testing.
Every migrated module had to meet our testing standards before it could be deployed. This slowed us down initially, but it gave us the confidence to refactor aggressively when we found better approaches. The safety net of automated tests meant we could iterate without fear.
Deployment and Real-World Impact
We rolled out the migration in phases, country by country. Each deployment taught us something new about performance optimization, caching strategies, and the quirks of different data formats. The modular architecture paid off—when we discovered an issue in one module, we could fix and redeploy it without touching the rest of the system.
Today, EUCARIS runs on .NET 8 with a modern Blazor frontend, comprehensive test coverage, and a cleaner architecture that makes new features easier to implement. Response times are faster, the codebase is more maintainable, and our team has grown significantly in their understanding of modern .NET development.
Key Takeaways
- Start with testing: Establish your safety net before you start breaking things
- Modularize early: Breaking the monolith into modules makes migration manageable
- Phase the rollout: Gradual deployment reduces risk and surfaces issues early
- Invest in architecture: Clean separation of concerns pays dividends in maintainability
- Team learning: Budget time for the team to learn new technologies properly