Relationship with other projects

bootc is the key component in a broader mission of bootable containers. Here's its relationship to other moving parts.

Relationship with podman

It gets a bit confusing to talk about shipping bootable operating systems in container images. Again, to be clear: we are reusing container images as:

  • A build mechanism (including running as a standard OCI container image)
  • A transport mechanism

But, actually when a bootc container is booted, podman (or docker, etc.) is not involved. The storage used for the operating system content is distinct from /var/lib/containers. podman image prune --all will not delete your operating system.

That said, a toplevel goal of bootc is alignment with the ecosystem, which includes podman. But more specifically at a technical level, today bootc uses skopeo and hence indirectly containers/image as a way to fetch container images.

This means that bootc automatically also honors many of the knobs available in /etc/containers - specifically things like containers-registries.conf.

In other words, if you configure podman to pull images from your local mirror registry, then bootc will automatically honor that as well.

The simple way to say it is: A goal of bootc is to be the bootable-container analogue for podman, which runs application containers. Everywhere one might run podman, one could also consider using bootc.

Relationship with Image Builder (osbuild)

There is a new bootc-image-builder project that is dedicated to the intersection of these two!

Relationship with Kubernetes

Just as podman does not depend on a Kubernetes API server, bootc will also not depend on one.

However, there are also plans for bootc to also understand Kubernetes API types. See configmap/secret support for example.

Perhaps in the future we may actually support some kind of Pod analogue for representing the host state. Or we may define a CRD which can be used inside and outside of Kubernetes.

Relationship with rpm-ostree

Today both bootc and rpm-ostree use the ostree project as a backing model. Hence, when using a container source, rpm-ostree upgrade and bootc upgrade are effectively equivalent; you can use either command.

However with rpm-ostree (or, perhaps re-framed as "dnf image"), it will continue to work to e.g. dnf install (i.e. rpm-ostree install) on the client side system. In addition there are other client-side mutation commands such as rpm-ostree initramfs --enable.

However, as soon as you mutate the system in this way, bootc upgrade will error out as it will not understand how to upgrade the system. The bootc project currently takes a relatively hard stance that system state should come from a container image.

The way kernel argument work also uses ostree on the backend in both cases, so using e.g. rpm-ostree kargs will also work on a system updating via bootc.

Overall, rpm-ostree is used in several important projects and will continue to be maintained for many years to come.

However, for use cases which want a "pure" image based model, using bootc will be more appealing. bootc also does not e.g. drag in dependencies on libdnf and the RPM stack.

bootc also has the benefit of starting as a pure Rust project; and while it doesn't have an IPC mechanism today, the surface of such an API will be significantly smaller.

Further, bootc does aim to include some of the functionality of zincati.

But all this said: It will be supported to use both bootc and rpm-ostree together; they are not exclusive. For example, bootc status at least will still function even if packages are layered.

Future bootc <-> podman binding

All the above said, it is likely that at some point bootc will switch to hard binding with podman. This will reduce the role of ostree, and hence break compatibility with rpm-ostree. When such work lands, we will still support at least a "one way" transition from an ostree backend. But once this happens there are no plans to teach rpm-ostree to use podman too.

Relationship with Fedora CoreOS (and Silverblue, etc.)

Per above, it is a toplevel goal to support a seamless, transactional update from existing OSTree based systems, which includes these Fedora derivatives.

For Fedora CoreOS specifically, see this tracker issue.

See also OstreeNativeContainerStable.