clr - No AppDomains in .NET Core! Why?

Question

Is there a strong reason why Microsoft chose not to support AppDomains in .NET Core?

AppDomains are particularly useful when building long running server apps, where we may want to update the assemblies loaded by the server is a graceful manner, without shutting down the server.

Without AppDomains, how are we going to replace our assemblies in a long running server process?

AppDomains also provide us a way to isolate different parts of server code. Like, a custom websocket server can have socket code in primary appdomain, while our services run in secondary appdomain.

Without AppDomains, the above scenario is not possible.

I can see an argument that may talk about using VMs concept of Cloud for handling assembly changes and not having to incur the overhead of AppDomains. But is this what Microsoft thinks or says? or they have a specific reason and alternatives for the above scenarios?

Answer 1

Update for .NET Standard 2 and .NET Core 2

In .NET Standard 2 the AppDomain class is in there. However, many parts of that API will throw a PlatformNotSupportedException for .NET Core.

The main reason it's still in there is for basic stuff like registering an unhandled exception handler which will work.

The .NET Standard FAQ has this explanation:

Is AppDomain part of .NET Standard?

The AppDomain type is part of .NET Standard. Not all platforms will support the creation of new app domains, for example, .NET Core will not, so the method AppDomain.CreateDomain while being available in .NET Standard might throw PlatformNotSupportedException.

The primary reason we expose this type in .NET Standard is because the usage is fairly high and typically not associated with creating new app domains but for interacting with the current app domain, such as registering an unhandled exception handler or asking for the application's base directory.

Apart from that, the top answer and other answers also nicely explain why the bulk of AppDomain was still cut (e.g. throws a not supported exception).