This post is just a short summary on how to use buildah to build multi-architecture containers.

Building multi-architecture containers (e.g. x86_64 and arm64) is an easy task using docker buildx, e.g.

docker buildx build --platform linux/amd64,linux/arm64 -t feldspaten.org/my-multi-arch-container

However, the buildx command does not exists in podman natively. Here buildah can be used in conjunction with OCI image manifests and image indices. Image manifest can reference platform-specific versions of an image. Since I didn’t got all the details yet, let’s for now just start with how you can use buildah to create multi-platform containers, shall we?

Pre-requirements

• buildah (duh!) - comes typically with podman
• qemu packages for the desired target architecture

For the qemu packages, ensure that e.g. qemu-aarch64 is installed. On openSUSE Tumbleweed the following might give you a good selection

zypper in qemu-arm qemu-extra

Building

The workflow you need to follow is the following:

1. Create a manifest
2. Build for your desired architectures
3. Push the manifest to the registry

# Manifest name, can be anything
export MANIFEST="myapp-multiarch"
# Where to push to
export IMAGE="ghcr.io/user/image:v1.0.0"

# Create manifest
buildah manifest create "$MANIFEST"

## Add here your architectures. One build per architecture

# Build container for amd64 (x86_64) and arm64 (aarch64). Add more architectures as needed
buildah build --arch amd64 --tag "$IMAGE" --manifest "$MANIFEST" .
buildah build --arch arm64 --tag "$IMAGE" --manifest "$MANIFEST" .

# Push the manifest, this will include all architectures you build for before
buildah manifest push --all "$MANIFEST" "docker://$IMAGE"

And that’s it. Using this process you should be able to build and push a custom multi-arch OCI container using buildah