Produce an image as .tar.gz

[stan-sz]

Can the SDK produce the docker image as a local .tar.gz as in docker save comand?

[baronfel]

Not yet, but it's definitely something that is doable. Jib does it, for example. Is this something you'd be interested in digging into? We'd need

• a way to signal this from MSBuild properties
• a new 'output' mechanism in the CreateNewImage build task that would stream the generate archive similar to the existing Docker.Load API, but directly to a file.

[stan-sz]

Thanks for the hints. I cannot dig to it at the moment, but it's up-for-grabs for anyone willing to.

[MattKotsenas]

This is something I'd be interested in as well. I'm new to this project, but if it's something that is easy for a new person to get ramped up on, I'd be willing to contribute here.

[rainersigwald]

Awesome @MattKotsenas! I'll assign to you.

This should be fairly straightforward to implement, but will require some thought about how the user will request it.

The implementation will be very close to this part of the LocalDocker workflow:

sdk-container-builds/Microsoft.NET.Build.Containers/LocalDocker.cs

Lines 40 to 60 in 86ad140

	public static async Task WriteImageToStream(Image x, string name, string tag, Stream imageStream)
	{
	TarWriter writer = new(imageStream, TarEntryFormat.Gnu, leaveOpen: true);
	// Feed each layer tarball into the stream
	JsonArray layerTarballPaths = new JsonArray();
	foreach (var d in x.LayerDescriptors)
	{
	if (x.originatingRegistry is {} registry)
	{
	string localPath = await registry.DownloadBlob(x.OriginatingName, d);
	// Stuff that (uncompressed) tarball into the image tar stream
	// TODO uncompress!!
	string layerTarballPath = $"{d.Digest.Substring("sha256:".Length)}/layer.tar";
	await writer.WriteEntryAsync(localPath, layerTarballPath);
	layerTarballPaths.Add(layerTarballPath);
	}
	else

That creates a stream basically equivalent to what docker save does, but doesn't save it to disk, instead it streams it to docker load's stdin. If you were to instead put it in a file, that would be a big step here!

[Danielku15]

I opened a proposal for a new option here: #375

I have successfully used a similar approach on my earlier changes where I added the Windows Container Support and fixed the Tar format writing for LCOW.

There are still some design decisions to take but the PR might give a base for discussion:

• How to handle the multiple output file naming (is it even needed to have multiple tars for all 'destinations')
• New dedicated option vs. a local file ILocalDaemon
• (anything else?)

[stan-sz]

Thank you @Danielku15!

[baronfel]

Closing because @Danielku15 implemented this in dotnet/sdk#35151, which will ship in .NET 8.0.100 RC2.