Migrate .NET Framework to .NET Core

As Microsoft continues to focus on modern, cross-platform development, many organizations are choosing to migrate from .NET Framework to .NET Core (now unified as .NET 6/7/8). Migrating improves performance, scalability, cloud readiness, and long-term support.

This post outlines a step-by-step guide to upgrade .NET Framework applications by migrating from .NET Framework to .NET Core, along with best practices, challenges, and tools to ensure a smooth transition.

Migrate .NET Framework to .NET Core

Getting Started

As digital transformation accelerates, businesses are under constant pressure to modernize their applications to remain competitive, secure, and scalable. Many enterprise applications built on .NET Framework have served organizations well for years; however, with Microsoft shifting its innovation focus to .NET Core and the unified .NET platform, continuing to rely on legacy technology can limit growth and increase maintenance costs.

.NET Framework is now in maintenance mode, meaning it receives only critical security updates and no new feature enhancements. In contrast, .NET Core and modern .NET versions (6, 7, and 8) are actively developed, offering improved performance, cross-platform support, cloud-native capabilities, and long-term support (LTS). This shift has made migration from .NET Framework to .NET Core not just a technical upgrade, but a strategic business decision.

Migrating to .NET Core allows organizations to:

• Build high-performance, scalable applications
• Deploy seamlessly to cloud, containers, and microservices
• Reduce infrastructure costs
• Adopt modern development practices such as DevOps and CI/CD
• Ensure long-term support and future readiness

However, migration is not a simple “lift and shift.” It requires careful planning, dependency analysis, architectural adjustments, and thorough testing. Understanding the migration process, potential challenges, and best practices is critical to ensuring a successful transition with minimal disruption.

Here in the below are the comprehensive step-by-step guide to migrating from .NET Framework to .NET Core, helping developers, architects, and IT leaders modernize their applications efficiently while minimizing risk.

Tools to use: These tools help identify incompatible APIs and estimate migration effort.

• .NET Portability Analyzer
• Microsoft Upgrade Assistant
• API Analyzer

.NET Core Migration Steps

1. Assess Your Existing Application
   • Start by analyzing your current .NET Framework application.
   • Use above tool to analyze, This helps identify incompatible APIs and estimate migration effort.
2. Choose the Right Target .NET Version
   Instead of migrating to early .NET Core versions, target the latest Long-Term Support (LTS) version such as:
   • .NET 6 (LTS)
   • .NET 8 (LTS)
3. Upgrade Project Files
   • Convert old .csproj files to SDK-style projects
   • Remove unused references and legacy configurations
   • Replace packages.config with PackageReference
   • Microsoft’s Upgrade Assistant can automate much of this process.
4. Update Packages and Dependencies
   • Update all NuGet packages to .NET Core–compatible versions
   • Replace unsupported libraries with modern alternatives
   • Prefer Microsoft.Extensions libraries for logging, configuration, and dependency injection
   • Check package compatibility using nuget.org or Visual Studio’s dependency manager.
5. Replace Unsupported APIs: Some .NET Framework APIs are not available in .NET Core.Use abstraction layers to minimize future migration issues.
6. Migrate Application Architecture
   • Web Applications:
     • ASP.NET MVC → ASP.NET Core MVC
     • ASP.NET Web API → ASP.NET Core Web API
     • Use middleware instead of HTTP modules
   • Desktop Applications:
     • WPF and Windows Forms can be migrated to .NET Core / .NET 6+
     • Test Windows-specific features carefully
   • Services:
     • Windows Services → Worker Services
     • Consider Docker containers or Azure App Services
7. Update Configuration and Environment Settings
   • Replace web.config and app.config with appsettings.json
   • Use environment-based configuration
   • Store secrets securely using Azure Key Vault or User Secrets
8. Test Thoroughly
   • Unit tests
   • Integration tests
   • Regression testing
   • Performance benchmarking

Summary

Migrating from .NET Framework to .NET Core is a strategic investment that improves performance, scalability, and future readiness. By following a structured migration approach(assessment, modernization, testing, and deployment), you can reduce risk and maximize long-term benefits. With Microsoft’s ongoing innovation in .NET, now is the ideal time to modernize your applications.

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