buildah bud --platform functionality missing

[TomSweeneyRedHat]

Description
buildah bud --platform is missing and needs to be provided. This is functionality that Docker has.

#599 is the parent issue for this issue.

Output of buildah version:

Buildah v0.16

[pixdrift]

@TomSweeneyRedHat, need minor edit to issue name to add --platform

[TomSweeneyRedHat]

@pixdrift, darn tricky cut/paste tricks. TY!

[TomSweeneyRedHat]

OK, tried to reset the title one more time....

[rhatdan]

Does anyone know what this is. Probably something like

buildah bud --platform i686 and then allows you to create 32 bit containers on a a 64 bit machine?

[TomSweeneyRedHat]

@rhatdan, you're example is my understanding of what --platform does, or at least is intended to do.

[rhatdan]

I guess this would only inform the from command or buildah command to tell containers/image to pull images with that architecture. Probably would not be that difficult.

WDYT @mtrmac

[mtrmac]

Sure, c/image can be told which platform (and which OS) to use when pulling images (types.SystemContext.ArchitectureChoice, types.SystemContext.OSChoice). That’s trivial.

I don’t know how RunC deals with cross-architecture containers, and it will make it much more noticeable that the host and container environments may differ for buildah users, e.g. somebody will need to make sure dnf --installroot ${buildah_mounted_dir} does the right thing (and can work at all), or document the necessary extra options. I suppose as long as the kernel can executables for the target platform at all (i.e. mostly 32-on-64, same architecture), it should all be possible but it may get tricky. (Or maybe this has all been extensively researched, tested, and is known to work, and I’m just unaware.)

After implementing this, at some point the question of creating (not just consuming) multi-arch images will probably come up, i.e. something like containers/podman#713 or a related Buildah feature.

[rhatdan]

@vrothberg or @umohnani8 Would you like to take a look at this?

[vrothberg]

@vrothberg or @umohnani8 Would you like to take a look at this?

I can start looking into it next week. But @umohnani8, feel free to tackle it before if you want to :)

[vrothberg]

Does anyone know what this is. Probably something like

buildah bud --platform i686 and then allows you to create 32 bit containers on a a 64 bit machine?

The semantics of the --platform flag are actually quite different. In this context, platform refers to Linux, Windows, etc. and is mainly used to support use-cases for Docker on Windows where Linux images can be executed via Hyper-V.

I think that we cannot support it 🙉 but we could add this flag (and maybe similar cases) as a nop? @rhatdan WDYT?

[rhatdan]

SGTM