Confusion about tags

[Antonytm]

I look on page https://hub.docker.com/_/microsoft-dotnet-framework-sdk/

I see that Windows Server Core 2022 build has tags 4.8, latest
I see that Windows Server Core, version 20H2 build has tags 4.8, latest
I see that Windows Server Core 2019 build has tags 4.8, latest
I see that Windows Server Core 2016 build has tags 4.8, latest

As many versions have the same tag, I am confused, about what version will be used, when I will write:

docker pull mcr.microsoft.com/dotnet/framework/sdk:4.8 

?

[richlander]

It depends on your Windows (Client or Server) version. I am not sure if that is documented anywhere.

You can pull the image and then check which Windows Server Core version you pulled. Does that work?

[Antonytm]

I have Windows 10 21H1 locally, I pull mcr.microsoft.com/dotnet/framework/sdk:4.8, I got Digest: sha256:296a507e6fe9cadd75a31a8781fccaf747447d66bcc51463abb705f8cab7b60b.

Then I repeat the same in Github actions using windows-latest, which is windows server 2022. I checked digest, it is the same 296a507e6fe9cadd75a31a8781fccaf747447d66bcc51463abb705f8cab7b60b.

@richlander Should I get different versions?

[mthalman]

The 4.8 is a manifest list (multi-platform) tag. Docker will automatically resolve that tag to an actual image based on rules governed by the metadata of the manifest list. For Windows, those rules make use of the Windows version. It will attempt to find an image that matches the Windows version of the host.

If we take a look at manifest list, we can see what we're dealing with:

C:\> docker manifest inspect mcr.microsoft.com/dotnet/framework/sdk:4.8
{
   "schemaVersion": 2,
   "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json",
   "manifests": [
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 3206,
         "digest": "sha256:fb80acb2729830be7b7e7f2a9be061a9ffa72f33a2fbe9fc75aed84f46857088",
         "platform": {
            "architecture": "amd64",
            "os": "windows",
            "os.version": "10.0.14393.5192"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 2788,
         "digest": "sha256:82e0a5e2c8747b9f2c88a15e7f652fd4b437cbe0399ab15ac54a0680dde8b453",
         "platform": {
            "architecture": "amd64",
            "os": "windows",
            "os.version": "10.0.17763.3046"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 2580,
         "digest": "sha256:e93be4dcc24e1327ec07e843c5b391e7c84dc9897b2deebb813b06f3547c0745",
         "platform": {
            "architecture": "amd64",
            "os": "windows",
            "os.version": "10.0.19042.1766"
         }
      },
      {
         "mediaType": "application/vnd.docker.distribution.manifest.v2+json",
         "size": 2579,
         "digest": "sha256:6c490f4528cb625c60aa119669830639ae3988c3c23dfb2f94a4ef19df2eb606",
         "platform": {
            "architecture": "amd64",
            "os": "windows",
            "os.version": "10.0.20348.768"
         }
      }
   ]
}

That metadata provides a mapping between image digests and Windows version. So there's a registration for digest sha256:6c490f4528cb625c60aa119669830639ae3988c3c23dfb2f94a4ef19df2eb606 that is based on Windows Server 2022 (10.0.20348.768). So if you pulled the 4.8 tag on a Windows Server 2022 machine, that's the image you'd get.

Windows desktop versions are more problematic now that Windows Server has moved to releasing Windows Server versions only for LTSC (long term support channel) versions and not SAC (semi-annual channel). This means your Windows 10 21H1 (version 10.0.19043) machine doesn't have a matching Windows Server container version. This is true for all of Windows Server containers, not specifically .NET Framework containers. Because no match is found, it falls back to the first version in the manifest list, version 10.0.14393.5192, which is Windows Server 2016.

If you want to be explicit about which version you get on your desktop machine, you'd need to use a tag which specifies the Windows version. For example, if you want the Windows Server 2022 image, you'd need to use the 4.8-windowsservercore-ltsc2022 tag. This kind of workaround is only really needed for desktop scenarios. When running from a Windows Server machine, you'll always get a direct matching version when targeting just the 4.8 tag.

One trick you could do with your Dockerfile is to make use of an ARG that allows you to override the tag for desktop scenarios:

ARG NET_FX_TAG=4.8
FROM mcr.microsoft.com/dotnet/framework/sdk:$NET_FX_TAG

To use this from the command line you would use the --build-arg option: docker build --build-arg NET_FX_TAG=4.8-windowsservercore-ltsc2022 -t my-tag .

Side note regarding the digest you had provided:

Digest 296a507e6fe9cadd75a31a8781fccaf747447d66bcc51463abb705f8cab7b60b refers to the sdk:4.8 manifest list. It doesn't refer to the underlying image that actually gets resolved and pulled down. So that digest doesn't help indicate what image was pulled.

[Antonytm]

@mthalman

Thank you! That is a very good explanation!

Is there any quick way to compare configurations for different platforms?

I had an issue with differences in the default shell on windows-2019 and windows-2022
I know that the default shell on Windows 10 is PowerShell by running the command:
docker inspect mcr.microsoft.com/dotnet/framework/sdk:4.8

            "Cmd": [
                "powershell",
                "-Command",
                "$ErrorActionPreference = 'Stop'; $ProgressPreference = 'SilentlyContinue';",
                "#(nop) ",
                "SHELL [powershell -Command $ErrorActionPreference = 'Stop'; $ProgressPreference = 'SilentlyContinue';]"
            ],

And for windows-2019 it is also PoserShell.
But for windows-2022, it is cmd.

But I am not even able to run locally docker inspect mcr.microsoft.com/dotnet/framework/sdk:4.8-20220614-windowsservercore-ltsc2022 and compare because I am on Windows 10. And to run it on a server I needed to add this step into CI.

[mthalman]

Is there any quick way to compare configurations for different platforms?

The simplest way would probably be to just use a file comparison tool to compare the Dockerfiles that are in this repo. So you could compare sdk:4.8-windowsservercore-ltsc2019 to sdk:4.8-windowsservercore-ltsc2022.

I had an issue with differences in the default shell on windows-2019 and windows-2022

Yes, setting the shell to PowerShell was something that specifically existed in the WS 2019 SDK Dockerfile. It was then later changed as part of the release of Windows Server 20H2 and documented at that time: #925.