Apm-agent-dotnet: Move to .NET Core 3.0

[gregkalapos]

• Both tooling and CI - especially for local tools mentioned here
• Also we should have sample apps exercising the agent on .NET Core 3.0. and also with ASP.NET Core 3.0

[vhatsura]

Hey, @gregkalapos. Do we have any updates on it? .Net Core 3.0 will allow using C# 8.0 to simplify code in some places.

[gregkalapos]

@vhatsura no update yet, we did not do any work yet.

[vhatsura]

@vhatsura no update yet, we did not do any work yet.

Do you have smth we, as a community, can do it to help your team?

[gregkalapos]

@vhatsura no update yet, we did not do any work yet.

Do you have smth we, as a community, can do it to help your team?

@vhatsura I think a good first step would be to make sure we have test coverage for 3.0 - if we'd make both the Elastic.Apm.Tests and the Elastic.Apm.AspNetCore.Tests run both on 2.1 and 3.0 (actually 2.2 would be also nice) that would be already a good first step.

I guess Elastic.Apm.Tests can be done by multitargeting, Elastic.Apm.AspNetCore.Tests is more challenging, since that depends on the ASP.NET Core version.

If we would have that, we would already discover things like #604.

[gregkalapos]

Let's start working on this!

I see @vhatsura already opened some PRs, which is awesome.

I think there will be multiple steps needed.

1.
First we have to make sure CI is able to build 3.x - I started working on it in #638.

1. 
   Then we can update the projects to target netcoreapp3.x - that is done in #622 (thanks for that!)

3.
And then once that's done we need to fix all the tests and fix some bugs (we already know about #632 - and I think I also saw that on 3.x the default service name detection does not work either, and maybe there are other things.

Now, until step 3. is not done we won't have a green build, so I'd propose doing this work on a separate branch and once that's green we can merge the whole thing to master. I created a branch NetCore3 - let's direct all 3.x related PRs to that branch. With that it's fine to merge things that are not green into that branch - everything that moves us to get closer to have 3.x is fine to merge. Please only do PRs that are about targeting 3.x - no refactorings, logical changes, etc - those can be done against master later if needed.

Another suggestion is that we go with the 3.1 SDK version which came out a couple of days ago. It's the LTS version (3.0 is not LTS), and it is basically 3.0 plus some minor fixes, so if 3.0 works I assume 3.1 will be just an additional target.

[gregkalapos]

Current status:

I moved a bunch of things to the NetCore3 branch.

CI:

• Linux: fails - The linux stage runs in docker, my idea is to use the 3.1 base image and additionally install the 2.1 sdk into it - I spent some time on it with no success. I'll ping the automation team, they know jenkins better.
• Windows - .NET Framework: fails, the current MSBuild version is too old for .NET Core SDK 3.1 - added to https://github.com/elastic/observability-dev/issues/389.
• Windows .NET Core: build green, but tests fail - the log output is strange - it does not reveal any info. More details: https://github.com/elastic/apm-agent-dotnet/pull/644#issuecomment-562967206

Targetframeworks:
netcoreapp3.1 is missing, I'll add it.

Tests:
All green locally on my machine.

Next step:
Tomorrow I'll talk to the automation team about the CI - I think we can make the Linux and Windows .NET Core stages green fast.

[vhatsura]

Targetframeworks:
netcoreapp3.1 is missing, I'll add it.

Thanks for your update. I share my thoughts about an additional for netcoreapp3.1 in https://github.com/elastic/apm-agent-dotnet/pull/622#discussion_r355208948.
It would be nice to hear your feedback about it

[gregkalapos]

Update:

In #646 @v1v prepared CI for all the new targetframeworks.

647 is getting close to being ready to review and merge.

[gregkalapos]

Done in #647.