Question: I was about to use the existing Serilog's SQL Server sink but I realized that the latest pre-release and stable versions do not support ASP.NET Core. 

Is there an alternative to this sink? What am I supposed to do? Should I write a new sink?

Answer: 
The [Serilog sink for SQL Server](https://github.com/serilog/serilog-sinks-mssqlserver) depends on some types not yet in .NET Core. Work started to refactor the sink and remove the dependencies, but since then, the types in question have been added to the next .NET Core version:

<https://github.com/dotnet/corefx/pull/12426>

Due to this, the Serilog SQL Server sink will most likely remain .NET Framework-only until the next .NET Core/.NET Standard release, after which support will be quick to add.

In the interim, writing a quick implementation of `ILogEventSink` of your own would be a reasonable way to get unblocked.
I guess the question is not really technical, but rather a philosophical one, then I do not propose an answer, but consideration:

In my humble opinion, Microsoft with its Silverlight killing, UWP orientation and "escape to clouds", admitted defeat of its entire concept of proprietary software development, so liberation of dotnet platform is nothing more than the farewell gift for developers, deceived in their hopes.

By itself, dotnet ecosystem is very promising, but its future has little to do with the Microsoft products, as it was before. At least, I hope as a developer who has been working with Microsoft products more then twenty years. Therefore, common infrastructure libraries that were focused on concrete Microsoft products (I mean MS SQL Server in this current case) are dying now.

Therefore, the conclusion is: if you already have long-term project that tightly coupled with SQLServer, maybe it is better to put some efforts to your current logging solution adaptation, otherwise it is better to look for some logging solution, not dependent on MSSQL. Probably it should support different storages via adapters or something like that. 

Try to look at [this](http://nlog-project.org/), they declare Core support in next version, at least this is a live project.