icu-libs in Alpine SDK but not runtime

[brettrowberry]

Describe the Problem

In .NET 5 Alpine SDK images, icu-libs are included - but not in the runtime images.

Describe the Solution

Include or remove icu-libs from both images.

Additional Context

See https://andrewlock.net/dotnet-core-docker-and-cultures-solving-culture-issues-porting-a-net-core-app-from-windows-to-linux/

[richlander]

Good issue. We need to make a final decision on #1877 within the 6.0 release. That will help us resolve this issue.

[brettrowberry]

Thanks @richlander! I want the leanest .NET 5 (and beyond) images I can get. I want to minimize local dev setup time and CI build time.

[brettrowberry]

And I don’t want different behavior building/testing apps vs running them!

[richlander]

I agree with both of those sentiments! We'll see what we can do.

[mthalman]

I think the key here is with the setting of DOTNET_SYSTEM_GLOBALIZATION_INVARIANT to false. We can control that in the SDK by not setting that way. We can also avoid explicitly installing icu, but we can't necessarily guarantee that it won't exist due to a dependency on some other package that we do install. For example, in the sdk we install git. Today it doesn't have a dependency on icu but we can't necessarily guarantee it won't some day.

[lbussell]

Alpine images with ICU libs are now available with the -extra image variant: https://github.com/dotnet/dotnet-docker/blob/main/documentation/image-variants.md#extra-net-80