proposal: Support apple container

[janishorsts]

Use case

@EarthBuild runs the buildkit instance in Docker or Podman on macOS.

Expected Behavior

Add support for the apple container on macOS.

[kmannislands]

Having less to install on macos would be quite nice. Are there anticipated performance benefits?

[janishorsts]

@kmannislands, yes. Not only performance benefits (fs, networking and so on), but also security and isolation. More https://www.infoq.com/news/2025/06/apple-container-linux/.

Container CLI is not pre-installed in macOS. Yet.

[janishorsts]

v1 has been released.

[gilescope]

Sibling proposal for the Windows-native equivalent: #602 (wslc / WSL Containers). Both are "add a non-Docker ContainerFrontend", same seam as the Podman work.

Some research notes for whoever picks this up:

The seam is already there. util/containerutil/frontend.go defines the ~14-method ContainerFrontend interface; docker.go / podman.go are shell impls. Add an apple-container impl + a frontend constant.

Load-bearing unknown — spike first: apple/container has no --privileged, only --cap-add. Must confirm buildkitd boots rootless / with explicit caps. If it can't, this is shim-only.

gRPC transport: no docker-container:// connhelper for apple/container → use tcp://<container-ip>:<port> (Podman already does TCP; apple/container's per-container IP is host-reachable). Extend the scheme allowlist in shell_shared.go:parseAndValidateURL().

Loose ends: new ImageLoadFromFileCommand variant; auth provider defaults to ~/.docker/config.json (build_cmd.go); regproxy hardcodes host.docker.internal (regproxy/controller.go). WITH DOCKER is not a blocker — dockerd-wrapper.sh runs dockerd inside the buildkit container, host-runtime-independent.

Near-term alternative: socktainer exposes a Docker REST API over apple/container → existing docker frontend, ~0 EarthBuild code (but inherits the privilege limits above).

Notably, apple/container itself already runs buildkitd internally via container-builder-shim, so buildkit-under-apple-container is proven in principle — the shim just isn't a general-purpose endpoint.

AI-assisted investigation.

[janishorsts]

Apparently, @dagger runs fine - apple/container#206