Kaniko doesn’t set image platform for FROM scratch images

[andrewshadura]

Actual behavior
When trying to pull an image generated with kaniko FROM scratch with podman, podman complains:

Trying to pull registry.tld/package-builder...
  Image operating system mismatch: image uses "", expecting "linux"
Error: unable to pull registry.tld/package-builder: unable to pull image: Image operating system mismatch: image uses "", expecting "linux"

Apparently, the platform is set only for images derived from others:

$ skopeo inspect docker://registry.tld/debian-based-image-builder | grep Os
    "Os": "linux",
$ skopeo inspect docker://registry.tld/package-builder | grep Os
    "Os": "",

Expected behavior
Set the platform value to an actual one or provide a way to override.

To Reproduce
Steps to reproduce the behavior:

FROM scratch

ADD rootfs.tar.gz /

Triage Notes for the Maintainers

Description	Yes/No
Please check if this a new feature you are proposing
Please check if the build works in docker but not in kaniko
Please check if this error is seen when you use --cache flag
Please check if your dockerfile is a multistage dockerfile

[em-]

My naive observation is that kaniko may be creating an empty manifest that is too empty when building an image from scratch:
https://github.com/GoogleContainerTools/kaniko/blob/master/pkg/executor/build.go#L444

Os and Architecture should probably be set if unset, just like it is done for Env:
https://github.com/GoogleContainerTools/kaniko/blob/a2aae627/pkg/executor/build.go#L139

Likely these values should be used by default (they don't seem to be used anywhere at the moment):
https://github.com/GoogleContainerTools/kaniko/blob/a2aae6274/pkg/util/util.go#L146

[tejal29]

Thanks @em for the details.
@andrewshadura oe @em- Would you any of you want to give it a try?

[sereinity]

Also, having os="" makes podman fail to run the container.

podman run …
Error: incompatible image OS "" on "linux" host

Do you prefer a separated issue ?