Obsolete TelemetryConfiguration.Active singleton usage on .NET Core

[lmolkova]

We have a stream of issues and support requests coming from confusion around TelemetryConfiguration.Active on ASP.NET Core.

We DO NOT recommend using TelemetryConfiguration.Active - instead we recommend using DI from Microsoft.Extensions.DependencyInjection.

In the case of ASP.NET Core or generic host applications, here is an instruction on how to use/configure TelemetryConfiguration: https://docs.microsoft.com/en-us/azure/azure-monitor/app/asp-net-core

This change makes Active obsolete on .NET Core to further discourage its usage there.

[cijothomas]

@lmolkova I wonder what would be our suggestion for .NET Core Console Apps which don't use DI, so using .Active probably okay there?
How can we handle this in code? we cannot detect .NET Core vs Asp.Net Core, and apply Obsolete tag.

[lmolkova]

I wonder what would be our suggestion for .NET Core Console Apps which don't use DI, so using .Active probably okay there?
How can we handle this in code? we cannot detect .NET Core vs Asp.Net Core, and apply Obsolete tag.

Console applications should carry all objects explicitly.
They should create the configuration with TelemetryConfiguration.CreateDefault() and carry it everywhere as any other object they create (e.g. DB client or Azure Storage client).

They can install DI extensions from Microsoft.Extensions.DependencyInjection and use DI pattern or use any other DI framework. They also can explicitly pass configuration/client around.

If they really want static singleton - it is their choice to store explicitly created instance in global static variable, but we should not promote it or do it ourselves.

If we decide to proceed with this change, we should update console app docs (and monitor other docs) to reflect this.
@Dmitry-Matveev @SergeyKanzhelev I hope to hear your opinion on this.

[Dmitry-Matveev]

@lmolkova , if docs are to be updated with the statements you outlined, I'm OK deprecating this in .NET Core branch.

[cijothomas]

I am okay with this change, but please ensure docs are updated by the time we ship beta1 with this change.
Other SDK repos will start showing compile errors for using things deprecated from this change. so need to change those as well.

[cijothomas]

its best to create a new issue in Github repo, and link to the above links from there. Main reason is - the above links are all 'asp.net core' specific, not so much about '.net core console'. So our Github issue can act as a wrapper, and have links to asp.net core with di, .net core with di, or just plain .net core console etc. (if needed).

Also it'd be good place for us to explain the rationale behind this decision in a github issue in this repo.