How Do I Migrate from .NET Framework to .NET 8 or 9?


If your application still runs on the .NET Framework, it’s likely time to consider a move. .NET 8—and soon, .NET 9—bring modern architecture, performance improvements, and long-term support that legacy projects miss out on. But making the shift from .NET Framework to .NET 8 or 9 isn’t as simple as updating a package. It’s a well-planned, multi-step process that touches code structure, dependencies, testing, and deployment.

In this blog, we’ll break down how to migrate efficiently and avoid the common pitfalls that stall teams mid-transition.

If you want to understand what the .NET Framework is, here are  7 Key Insights You Should Know. 

Why Migrate to .NET 8 or .NET 9?

Before diving into the migration steps, let’s understand the value of upgrading.

  • Performance: .NET 8 offers runtime performance that’s significantly faster than .NET Framework 4.x.
  • Cross-Platform Development: The new .NET is built to run on Windows, macOS, and Linux—freeing you from Windows-only environments.
  • Modern APIs: You get access to minimal APIs, gRPC, better support for containers, and cloud-native patterns.
  • Long-Term Support (LTS): .NET 8 is LTS, meaning extended support and updates through 2026. .NET 9, although a standard-term release, will introduce further advancements.

If you're using ASP.NET MVC or Web Forms on the legacy framework, note that these are not directly supported in the newer .NET versions. You'll need to re-platform to ASP.NET Core.


Step-by-Step Migration Guide

1. Evaluate Your Existing Application

Begin with a full assessment of the project. Determine:

  • The .NET Framework version in use
  • Dependencies and third-party libraries
  • Use of Windows-specific APIs or components (like WCF, Web Forms)
  • Architecture: monolith, layered, or microservices?

This evaluation will dictate the level of effort required and the migration path to follow. Use tools like .NET Upgrade Assistant and API Port Analyzer to assess compatibility.


2. Upgrade to .NET Standard (Optional)

If your application is split into multiple class libraries, consider upgrading them to .NET Standard 2.0 or 2.1 before moving to .NET 8 or 9. This makes libraries more portable and prepares them for the next step.

  • Projects targeting .NET Standard can often be reused directly in .NET 8 or 9.
  • Focus on isolating business logic from platform-specific code.


3. Migrate to SDK-style Projects

.NET Core, .NET 5+, and .NET 8/9 all use SDK-style project files. Legacy projects use older .csproj formats. Before continuing with a full migration:

  • Convert the project files manually or with tools
  • Remove redundant configuration lines
  • Define target frameworks appropriately (e.g., <TargetFramework>net8.0</TargetFramework>)

This step is crucial—SDK-style projects are cleaner, easier to maintain, and compatible with modern tooling.


4. Refactor Platform-Specific Code

.NET 8 and 9 no longer support certain legacy components like:

  • Web Forms: There is no direct path; consider Blazor or Razor Pages.
  • WCF: Use gRPC or RESTful APIs as alternatives.
  • System.Drawing (on non-Windows platforms): Use cross-platform alternatives like SkiaSharp.

Identify these areas and plan for alternatives during refactoring. This is also a good opportunity to modernize application architecture, for instance by introducing dependency injection or asynchronous programming patterns.


5. Rebuild the Application in .NET 8 or 9

Create a new project in .NET 8 or 9 using the appropriate project template:

  • For web apps: use aspnetcore-empty, webapi, or mvc
  • For services: use worker or console

Then, move the code in phases:

  • Business logic
  • Data access
  • Middleware
  • Frontend components (if using MVC or Razor)

Avoid a full "lift and shift." Instead, incrementally rebuild and test each module.


6. Test Thoroughly

Regression testing is vital. Ensure your migrated application behaves identically (or better) than the previous version. Use:

  • Unit tests for business logic
  • Integration tests for the database and service layers
  • Load testing for performance benchmarks

Remember, subtle changes in the runtime can introduce unexpected behaviors.


7. CI/CD and Deployment Adjustments

If you’re moving from a legacy deployment method (like FTP or Windows Services), you may also need to modernize the CI/CD pipeline:

  • Use GitHub Actions or Azure DevOps for builds
  • Containerize with Docker if needed
  • Configure deployment to cloud environments (e.g., Azure App Services, AWS, GCP)

The tooling around .NET 8 and .NET 9 integrates easily with DevOps workflows, reducing manual steps and improving consistency.


Common Migration Pitfalls to Avoid

  1. Assuming Compatibility: Many APIs from the .NET Framework don't exist in .NET 8/9. Always validate with tools.
  2. Skipping Architecture Review: A legacy monolith may require more than just code changes. Consider whether microservices or modular architecture makes sense now.
  3. Ignoring Tests: Lack of automated testing increases risk. Build a test suite before and during migration.
  4. Neglecting User Impact: End-users might notice performance changes or subtle UI differences. Communicate and validate with user feedback.


When Should You Hire .NET Developers?

Migration is technical and time-consuming. If your internal team lacks bandwidth or expertise, it’s worth exploring ASP.NET Development Services to assist with:

  • Architecture analysis and planning
  • Refactoring and modernization
  • QA and deployment strategies

Many businesses choose to hire .NET developers during this phase to minimize downtime and ensure alignment with modern development standards. The cost of poor migration is far higher than doing it right the first time.


Conclusion

Migrating from the .NET Framework to .NET 8 or 9 isn’t a quick fix—it’s a technical evolution. But with careful planning, code refactoring, and phased execution, you can unlock the benefits of performance, flexibility, and long-term viability.

If you're at a stage where you're evaluating the move or need assistance with legacy modernization, consider partnering with experts in ASP.NET Development Services. Whether it’s re-architecting a monolithic app or modernizing your web platform, the transition is a strategic step forward.


Read More: 

Choosing the Right Technology Stack for Your Social Media App

Overcoming Challenges in eLearning App Development

Best Angular Ide And Tools To Use For Web Development








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