.NET Framework Application Modernization
There’s more to .NET Framework modernization than porting code
You can view most applications through different lenses: the source code and runtime itself, the logical and system architecture, and the infrastructure it runs on. There are also cross-cutting concerns including observability, the build/test/release process, and the structure of your teams.
We recommend a holistic and iterative approach to modernizing these applications after a thorough assessment of their existing codebase and its dependencies and in alignment with your business and technical goals. A holistic approach modernizes across all the lenses and takes into account your team’s skills and tools. An iterative approach means progressively modernizing slices of functionality rather than a “big bang” approach which often leads to failure.
A Brief History of .NET
The Windows-only Era
Microsoft released .NET Framework 1.0 in 2002 as an application framework for Windows that included a common-language runtime, base class libraries, and support for multiple languages including VB.NET and C#. Additional versions were released over time, with 4.8.1 being the final release in 2022, which added support for arm64 processors. The first web application project type for .NET Framework was ASP.NET Web Forms in which HTML, CSS, JavaScript and server-side code are all intermingled on ASPX pages (which have the .aspx extension) and ASCX user controls. Later, Microsoft introduced the MVC project type (Model-View-Controller), and Web API (for REST APIs). The default C# version for .NET Framework is version 7.3, and many new language features in later C# versions are not compatible with .NET Framework (C# version 14 launches in 2025).
A new generation of .NET
In 2016, a new cross-platform, multi-architecture and open-source implementation of .NET was released by the .NET Foundation 
as .NET Core 1.0. Versions 2.x and 3.x quickly followed. After .NET Core 3.1, the platform was renamed to simply “.NET”, and the next version released was .NET 5. There is no .NET Core 4.x or .NET 4.x to avoid confusion with .NET Framework 4.x. Web applications built on .NET primarily use ASP.NET Core, which supports native project types for MVC, Web API, Razor Pages, Blazor / Blazor WebAssembly, and Worker Service. .NET Core 2.1 introduced support for the arm64 architecture, but .NET 5.0 introduced numerous optimizations that made it a compelling choice for cloud workloads.
Modernization takes off
Starting circa 2022, after the November 2021 release of .NET 6, an increasing number of organizations began modernization projects to convert their legacy Windows-bound .NET Framework applications to .NET 6 or higher, often with the goal of moving to Linux, containers and serverless, and on AWS Graviton arm64 processors when feasible.
.NET Framework Application Types and Modernization Level of Effort
There are a variety of application types built on .NET Framework that run in the AWS cloud. The most common we see are ASP.NET web applications, although most companies also run a variety of other application types. The level of effort to move to cross-platform versions of .NET to run on Linux varies tremendously by type. It’s also important to assess applications for Windows OS dependencies such COM objects, use of DLL imports, and NuGet packages that are Windows-specific as these will increase the effort to migrate from Windows to Linux.
| Application Type | Modernization Process | Target Application Type(s) | Level of Effort |
|---|---|---|---|
| Console application | Port using tools & GenAI | Console application | Low |
| .NET Windows Service | Port using tools & GenAI, manual intervention for lifecycle events | .NET Worker Service |
Low |
| WCF1 services | Port using tools, GenAI and developer effort | CoreWCF services |
Medium |
| ASP.NET Web API | Port using tools & GenAI, use of System.Web adapters | ASP.NET Core Web API | Medium |
| ASP.NET MVC | Port using tools & GenAI, use of System.Web adapters, some manual intervention required for UI | ASP.NET Core MVC | Medium |
| ASP.NET Web Forms | Web Forms UI must be re-implemented in another UI framework such as Blazor, unless the application can be run under Mono on Linux | ASP.NET Core Blazor2 Web Forms on Mono3 |
High Variable |
1 Windows Communication Foundation
2 While Blazor is the current recommendation, an emerging possibility for Web Forms is to port back-end code to .NET 8+ and leverage CoreWebForms , an open-source implementation of parts of the System.Web namespace, to run web forms and user controls in ASP.NET Core.
3 ASP.NET Web Forms applications can run on Linux using the open-source Mono implementation of the .NET runtime. However, this generally requires refactoring, and introduces troubleshooting challenges. This modernization path is not recommended for applications being actively developed.
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