Transactional, in-place operating system updates using OCI/Docker container images.
STATUS: Experimental, subject to change!
The original Docker container model of using "layers" to model applications has been extremely successful. This project aims to apply the same technique for bootable host systems - using standard OCI/Docker containers as a transport and delivery format for base operating system updates.
The container image includes a Linux kernel (in e.g. /usr/lib/modules),
which is used to boot. At runtime on a target system, the base userspace is
not itself running in a container by default. For example, assuming
systemd is in use, systemd acts as pid1 as usual - there's no "outer" process.
This project currently leverages significant work done in the ostree project.
In the future, there may be non-ostree backends.
The bootc project suggests that Linux operating systems and distributions to provide a new kind of "bootable" base image, distinct from "application" base images. See below for available images.
Effectively, these images contain a Linux kernel - and while this kernel
is not used when the image is used via e.g. podman|docker run, it is
used when booted via bootc.
In the current defaults, /etc and /var both act a bit like
mounted, persistent volumes. More on this in the ostree docs.
At the current time, bootc is in active development and is not quite considered ready for production use. The command line interface might change. There is not yet stable RPC API.
However, it heavily relies on a lot of underlying technologies which are tested, and the goal is to stabilize everything sometime in 2023.
- Fedora, CentOS Stream 9: There is a COPR tracking git main with binary packages.
You can also build this project like any other Rust project, e.g. cargo build --release from a git clone.
Many users will be more interested in base (container) images.
- The bootc-demo-base-images contains demonstration (relatively) small images that can be used as a starting point.
- Fedora CoreOS can also be used as a base image, but it does not currently include
bootc.
However, bootc itself is not tied to Fedora derivatives; and the plan is to extend the set of images.
A toplevel goal is that every tool and technique a Linux system administrator knows around how to build, inspect, mirror and manage application containers also applies to bootable host systems.
There are a number of examples in e.g. coreos/layering-examples.
First, build a derived container using any container build tooling.
The bootc install command will write the current container to a disk, and set it up for booting.
For example, booting a Fedora-derivative (including CentOS and RHEL) system, whether a cloud guest or a live ISO, you can invoke:
$ podman run --privileged --pid=host --net=none --security-opt label=type:unconfined_t ghcr.io/cgwalters/c9s-oscore bootc install --target-no-signature-verification /path/to/disk
As noted above though, if you create a derivative container image, it also automatically supports bootc install.
If you have an operating system already using ostree then you can use bootc switch:
$ bootc switch --no-signature-verification quay.io/examplecorp/custom:latest
This will preserve existing state in /etc and /var - for example,
host SSH keys and home directories. There may be some issues with uid/gid
drift in this scenario however.
Once a chosen container image is used as the boot source, further
invocations of bootc upgrade will look for newer versions - again
preserving state.
Today rpm-ostree directly links to ostree-rs-ext, and hence
gains all the same container functionality. This will likely
continue. For example, 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. However, bootc upgrade would
(should) then error out as it will not understand how to upgrade
the system.
rpm-ostree also has significant other features such as
rpm-ostree kargs etc.
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.