.NET Framework to .NET Core Migration Guidelines

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.NET Core is the latest evolution of the .NET platform, optimized for modern cloud workloads. As companies look to modernize their legacy .NET Framework applications, migrating to .NET Core offers many benefits, like improved performance, reduced resource usage, and cross-platform support. However, migration requires some planning and effort. This article provides key guidelines to follow when migrating an existing .NET Framework codebase to .NET Core.

Assess Readiness

Before beginning the migration process, assess the readiness of your .NET Framework application for a move to .NET Core:

  • Assess third-party library dependencies and discover whether there are more compatible versions for .NET Core or if there should be another one.
  • Verify whether the application relies on obsolete APIs and whether any of the newly implemented APIs of .NET Core are required to be updated.
  • Review the codebase for the usage of deprecated APIs which are already obsoleted and replaced by .NET Core.
  • List the elements a Windows-dependent app uses that need re-engineering to support multiple platforms.

This analysis will provide critical insights into the level of effort required and areas of focus to convert .NET Framework to .NET Core successfully.

Install Prerequisites

.NET Core has a different toolchain for building those applications, which should be installed prior to migration. Developer machines and build servers need to have .NET Core SDK installed for the compilation of the code. The Dotnet CLI tool is recommended for installation and configuration instead of MSBuild for .NET Core apps. Set up NuGet client applications to get .NET Core libraries and packages with the help of this application. And then lastly, put in IDEs such as Visual Studio or VS Code and later add any .NET Core development extensions. Appropriate assets will ensure that the development workflow for .NET Core performs better.

Port Code Gradually

It is rarely feasible to port an entire legacy codebase to .NET Core instantly. Instead, it works better to transition modules over time gradually:

  1. Identify and port over the presentation layer first, as it has the least dependencies
  2. Then, shift business logic modules with minimal ties to external systems or legacy libraries
  3. Port over data access layers using database provider packages compatible with .NET Core
  4. Finally, transition components with difficult dependencies requiring rewrites or refactoring

This incremental strategy prevents getting bogged down too quickly. Developers who provide .NET Framework to .NET Core Migration services can concentrate on isolated sections without having to make too many changes across the entire codebase simultaneously.

Leverage Compatibility Tools

Microsoft provides some useful compatibility tools that can simplify porting existing .NET Framework code over to .NET Core. The .NET Portability Analyzer highlights incompatible APIs and suggests alternatives to make things easier. Roslyn analyzers help by refactoring code to replace deprecated functions with newer ones. Runtime directives can be employed to selectively execute code depending on the environment (.NET Framework or .NET Core). Project.json configuration files can also map legacy library versions over to their .NET Core equivalents. These automated tools analyze codebases to significantly reduce overall migration effort and surface compatibility issues early on.

Refactor for New Best Practices

A migration is a good opportunity to re-evaluate programming best practices and employ better designs aligned with .NET Core:

  • Encapsulate shared application logic into NuGet packages for reuse across services
  • Implement dependency injection patterns to enable better testability and loose coupling
  • Employ asynchronous programming via async/await for scalable I/O heavy workloads
  • Containerize applications using Docker for simplified deployment and management

Refactoring with modern principles allows building .NET Core applications that feel truly next-gen rather than just lifted-and-shifted code.

Rigorously Test Application

Any migration of a legacy application risks potential regressions across functionality and performance. Hence, testing is crucial:

  1. Assemble a comprehensive regression test suite covering all major use cases and flows
  2. Stress test the application at load to detect performance bottlenecks
  3. Analyze test code coverage to find untested areas of code requiring attention
  4. Perform security testing and vulnerability scans to ensure no flaws were introduced
  5. Conduct A/B testing between old and new environments with representative user traffic

Thorough testing provides the safety net required when making major architecture changes underlying an application.


Migrating long-running .NET Framework applications to cloud-optimized .NET Core requires planning, strategic code transitions, leveraging compatibility tools, rearchitecting with the latest principles, and rigorous testing. Following these key guidelines will enable smooth modernization of the codebase while unlocking benefits like cross-platform support and improved scale and performance. With some concerted effort, companies can keep their legacy applications relevant for the next decade.


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