This post asked when 4.8 support would be available on Azure App Service: Azure support for .NET 4.8
A commenter asked if it's compulsory to update your apps as well, which is a great question.
Microsoft email blasted all app service customers so they seem to be taking this update pretty seriously, but didn't leave much time (July 14, 2020) if a full update is required.
The question is -- do we have to update to 4.8?
In short: Compulsory, no; advisable, yes.
Assuming your apps are already targeting a supported version of .NET (currently >= 4.5.2), then retargeting your apps to 4.8 is not compulsory. Particularly if you do not plan to take advantage of any new features. See .NET docs:
4.x versions of the .NET Framework can be used to run applications built for the .NET Framework 4.0 through that version. For example, .NET Framework 4.7 can be used to run applications built for the .NET Framework 4.0 through 4.7. The latest version (the .NET Framework 4.8) can be used to run applications built with all versions of the .NET Framework starting with 4.0.
As a minimum, you could run some regression tests against your app running on 4.8 before going live. How much testing it takes to gain confidence, and the chances of breaking changes, depends largely on what version you are currently targeting.
Ideally however, if you are in a position to retarget, build and deploy for 4.8, then a lot of unexpected behaviour can be caught even earlier by the compiler. Note that there are sometimes changes that require code changes and again, the likelihood depends very much on what you target at present.
To get an idea of what work you might need to do in your code:
Also worth noting that the likelihood of experiencing problems running an existing 4.x app on 4.8 without retargeting is lesser because:
the .NET Framework uses quirked behavior to mimic the older targeted version. The app runs on the newer version but acts as if it's running on the older version. Many of the compatibility issues between versions of the .NET Framework are mitigated through this quirking model.
EDIT: As of 26.6.2020 I am not aware of any plans to accommodate testing apps running in an App Service on 4.8 before the upgrade date, which means you will only be able to test on 4.8 locally.
As mentioned in the Azure App Service blog on this announcement - "The .NET Framework 4.8 update is a non-breaking in-place upgrade on App Service. No updates are required for existing applications."
However, if you do want to test your application or if you plan to re-target your application in the future to explicitly require .NET Framework 4.8 you are more welcome to do so but it is not required.
Based on your requirement, if are fine with running your applications with 4.6.1 as target so no action at this time is required from you. Our Product engineering team will update this announcement and the blog periodically to inform you of the deployment progress.
It would be nice if the Visual Studio 2017 updater supported 4.8. 4.7.2 is the latest version supported. Microsoft should get their ducks in a row before blindly sending out a bulk email implying an urgent update!
