.NET 9 Migration — Healthcare SaaS
From .NET Framework 4.6 to .NET 9. Zero regressions, 70x faster deployments.
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Project details
The problem
The SaaS application had been running on .NET Framework 4.6 for 8 years. Each deployment took an entire day with frequent regressions. The 40-developer team could no longer add features without risking breaking existing functionality. Hiring was becoming difficult — nobody wants to work on .NET Framework in 2025.
Our approach
Progressive migration using the “strangler fig” pattern: each new module is developed in .NET 9, and legacy modules are migrated one by one starting with the most critical ones. CI/CD pipeline set up from day one to secure every step.
What changed
- WCF / SOAP replaced by Minimal API REST
- ASP.NET MVC 5 / Razor migrated to Vue.js
- SQL Server with stored procedures migrated to PostgreSQL + EF Core
- Manual IIS deployment replaced by Docker + Azure DevOps CI/CD
Tech stack
Vue.js frontend with TypeScript. .NET 9 Minimal API backend with Entity Framework Core and PostgreSQL. Docker containerization for all services. Azure DevOps CI/CD pipeline with automated tests and continuous deployment.
Everything you need. Nothing more.
Strangler Fig Pattern
Progressive module-by-module migration. The old and new systems coexist without any service interruption.
CI/CD Azure DevOps
Automated pipeline from day one: build, tests, deployment in 20 minutes instead of a full day.
Docker containerization
Each service in its own container. Identical environments from development to production.
Automated testing
Test coverage on every migrated module. Zero regressions validated before each production release.
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