Support Alpine linux

[natemcmaster]

Requires compiling for musl, not glibc.

Workaround
Users can remove libuv from their app and rely on the system's installed version of libuv instead.

<ItemGroup>
  <PackageReference Include="Libuv" Version="1.10.0" ExcludeAssets="Native" />
</ItemGroup>

Then, install libuv on host machines.

apk add libuv
ln -s /usr/lib/libuv.so.1 /usr/lib/libuv.so

[muratg]

cc @glennc

[Petermarcu]

Can you flip back to using sockets to unblock temporarily?

[natemcmaster]

At the moment, Kestrel's default is still sockets in 2.1 preview1 bits. This default is subject to change before RTM. aspnet/KestrelHttpServer#2220

[Petermarcu]

Is see, I haven't seen the error for Alpine but what is blocking then? Is it that tests are failing on Alpine because they are explicitly running on libuv?

[natemcmaster]

Right. When I say it's a blocker, I mean blocking moving forward with Alpine in a supported way. We can disable tests, and produce a shared framework is broken for several key scenarios on Alpine...but I wouldn't want to ship that.

[Petermarcu]

We need to unblock product construction first. Alpine is already noted as a best effort OS and not in our supported list. Could you just disable the tests on Alpine? I also thought tests were not critical path for product construction

[natemcmaster]

Yes we can do those things. I updated my PR to the CLI last night to skip tests and pull our portable sharedfx even though it won't work. dotnet/cli#8341

[Petermarcu]

Sounds good. Thanks! Hopefully Alpine will be off the blocking list then.

[natemcmaster]

Punting to backlog as we want to make sockets the default transport in Kestrel. Users could workaround for now by installing the libuv apk.

[Petermarcu]

Did we make the call on switching to Sockets as the default for Kestrel? Can we drop the libuv package from the nuget dependency graph too?

[natemcmaster]

Yes. I’ll share our design meeting notes on Monday Sent from Outlook<https://aka.ms/qtex0l> for iOS

[natemcmaster]

Design meeting notes from March 2, 2018

See also aspnet/KestrelHttpServer#2360, aspnet/KestrelHttpServer#2361

[Petermarcu]

Do you want to support the All package and libuv transport on Alpine? If so, wouldn't you still need this issue?

[natemcmaster]

@muratg we should still probably consider this. Although you can workaround it with a globally installed libuv, it's not always easy to get that setup correctly.

[ghost]

@Petermarcu, @natemcmaster, I have built libuv binary on Alpine Linux with aspnet/libuv-build#34. Can this be shipped with 2.1? We can also build libuv for arm32 to match the dotnet-core supported platform matrix: aspnet/Universe#554.

[natemcmaster]

We are currently not planning on re-building the Libuv package to support Alpine in 2.1. However, we are still planning to enable ASP.NET Core for Alpine (already available in nightly builds, see https://hub.docker.com/r/microsoft/dotnet-nightly.) In 2.1, Kestrel will no longer rely on Libuv by default, so this issue isn't essential to getting ASP.NET Core + Alpine working.

We don't have plans to support arm32 in ASP.NET Core, at the moment.

[muratg]

Moved this to 3.0.0