buildah buildah is unable to push an image for a non-default platform

If I build an image for a non-default platform, e.g. i386 on amd64, armhf or armel on arm64, without building the image for the default platform, buildah is not able to push it. It complains because it doesn't find the default platform-image:

buildah push build-essential <registry>
Error: pushing image "build-essential" to "<registry>": no image found in image index for architecture amd64, variant "", OS linux: image not known

I can reproduce it locally with a simple Dockerfile:

FROM debian:unstable ARG ARCH=amd64 RUN apt-get update RUN apt-get -y install build-essential

and building it with:

buildah build --build-arg ARCH=i386 --platform "linux/i386" --manifest build-essential

The error comes from chooseInstance(): https://github.com/containers/image/blob/main/internal/manifest/oci_index.go#L264

Building the default platform additionally fixes the issue (I am able to push the image), but I need to avoid that.

Jul 17 '24 21:07 santiagorr

Thanks for your report.

If I understand the situation right, that behavior of c/image is, on its terms, correct. buildah build --manifest … creates a multi-platform image, and then buildah push is trying to push (what the code expects to be) a single-platform image without explicitly choosing a non-default platform.

Buildah’s code must choose to trigger a multi-platform push (or, alternatively, use options that let the user choose the desired platform for a single-platform push).

I suspect that code already exists in buildah, and this is already possible, using buildah manifest push or maybe buildah push --all, but I’m not immediately sure. Anyway, transferring to Buildah for these details.