Migrate to ASP.NET Core 2.1

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This content is an excerpt from the eBook, Porting existing ASP.NET Apps to .NET 6, available on .NET Docs or as a free downloadable PDF that can be read offline.

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ASP.NET Core 2.1 is an interesting release because it's the most recently supported ASP.NET Core release that supported both .NET Core and .NET Framework runtimes. As such, it may offer an easier upgrade path for some apps when compared to upgrading all parts of the app to .NET Core/.NET 6 at once. Although support for .NET Core 2.1 ended in August 2021, it may make sense as an interim step for some apps. Also, support for ASP.NET Core 2.1 running on .NET Framework will continue for as long as its underlying .NET Framework is supported. A complete list of currently supported ASP.NET Core 2.1 packages is available for reference.

Should apps run on .NET Framework with ASP.NET Core 2.1

ASP.NET Core 2.2 and earlier supported both .NET Core and .NET Framework runtimes. Does it make sense to migrate some or all of an app to ASP.NET Core 2.1 as a stepping stone, before porting over completely to .NET Core? Apps, or subsets of apps, could see their front-end ASP.NET logic ported to use ASP.NET Core, while still consuming .NET Framework libraries for business logic and infrastructure consumption. This approach may make sense when there's a relatively thin UI layer without much business logic, and a much larger set of functionality in class libraries.

The main benefit of porting just the front-end web layer to ASP.NET Core 2.1 is that the existing .NET class libraries can remain as is during the initial migration. They may be in continued use by other .NET apps or simply don't need to be in scope for the first iteration of a planned full migration to .NET Core. Reducing the scope of the initial migration for large apps helps provide incremental goals that act as stepping stones toward the desired end state, which is often a complete port to .NET Core.

If you have an existing app that may use this strategy, some things you can do today to help prepare for the process are to move as much business logic, data access, and other non-UI logic out of the ASP.NET projects and into separate class libraries as possible. It will also help if you have automated test coverage of your system, so that you can verify behavior remains consistent before and after the migration.

If your app is so large that you can't migrate the entire web app at once, and you need to be able to deploy the new ASP.NET Core app side-by-side with the existing ASP.NET app, there are deployment strategies that can be used to achieve this. These are covered in Chapter 5: Deployment Scenarios.

Keep in mind that ASP.NET Core 2.1 was the last LTS release of .NET Core that supported running on .NET Framework and consuming .NET Framework libraries. Although the release is now unsupported on .NET Core, it continues to be supported for use with .NET Framework. It will remain supported for as long as the specific .NET Framework version is supported. For more information, see ASP.NET Core 2.1 on .NET Framework.

References

Migrating from ASP.NET to ASP.NET Core 2.1 ASP.NET Core 2.1 on .NET Framework ASP.NET Core 2.1 Supported Packages

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