Changes/CoreOSOstree2OCIUpdates

Move Fedora CoreOS updates from OSTree to OCI

Summary

Change Fedora CoreOS to receive updates from quay.io/fedora/fedora-coreos instead of the Fedora OSTree repository.

Owner

• Name/Email: Jean-Baptiste Trystram, jbtrystram@redhat.com
• Name/Email: Timothée Ravier, siosm@fedoraproject.org
• Name/Email: Jonathan Lebon, jonathan@jlebon.com
• Name/Email: Dusty Mabe, dusty@dustymabe.com

Current status

• Targeted release: Fedora Linux 42
• Last updated: 2025-02-17
• Announced
• Discussion thread
• FESCo issue: #3359
• Tracker bug: #2346151
• Release notes tracker: #167

Detailed Description

Currently, Fedora CoreOS hosts pull updates from the OSTree repository. With this change, the hosts will pull updates from the Quay.io container registry instead. At first, this should be a transparent change. We will notably keep using rpm-ostree for updates (and not yet bootc).

This is preliminary work to switching to bootc to manage the system and will enable us to deliver the following changes in the future:

• Moving from rpm-ostree to bootc, which only supports OCI.
• Better support for mirroring updates in disconnected setups.
• Moving away from maintaining a Cincinnati server towards having the graph live in an OCI registry alongside the update payload. This also allows users to maintain their own update graphs.
• Users will be able to create their own customized versions of Fedora CoreOS by building a derived container image.

Note: Disk images will be updated first, so new installations of F42 based Fedora CoreOS will use OCI images. After a few releases, we will migrate existing nodes.

This change is only scoped to switching to OCI as the transport for Fedora CoreOS content. As before, derivation of Fedora CoreOS images is possible, but is still not fully supported.

Until we make progress on these topics, we recommend sticking to official images using Ignition and rpm-ostree to make your changes.

Feedback

None yet.

Benefit to Fedora

Alignment with the work happening in the Bootable Containers initiative.

Scope

• Proposal owners:
  • Publish an upgrade graph containing the digest pullspec for each FCOS release. This mirrors the current update graph containing the same information, but pointing at OSTree commit checksums.
  • Change new nodes on next to use OCI from the start.
  • After a number of FCOS releases, ship a migration script to switch existing next nodes to use OCI.
  • Repeat the last two steps for testing, and then stable.
  • Down the line, stop publishing new OSTree commits to the OSTree repo. This will not happen until at least f43.

• Other developers: N/A (not needed for this Change)
• Release engineering: N/A (not needed for this Change)
• Policies and guidelines: N/A (not needed for this Change)
• Trademark approval: N/A (not needed for this Change)
• Alignment with the Fedora Strategy:
  • Part of the work to align with Bootable Containers

Upgrade/compatibility impact

We will issue a barrier release to migrate users to switch to OCI images.

How To Test

Once the changes are ready, it will be possible to test it on the next stream before it gets rolled out there. This can be done by switching a next node from the OSTree remote to the OCI remote:

   rpm-ostree rebase ostree-remote-image:fedora:registry:quay.io/fedora/fedora-coreos:$NEXT_VERSION

where $NEXT_VERSION is a tag for a next release that's _not_ the latest. Then, watch Zincati fetch the latest next release using OCI.

User Experience

This change won't be visible to users running auto-updates, except cosmetic changes in rpm-ostree status output.

Contingency Plan

Revert the change to switch back to the OSTree repo. Both will be active until the Fedora 43 release.

Documentation

We will update the Fedora CoreOS documentation alongside the transition. This is currently tracked in: https://github.com/coreos/fedora-coreos-tracker/issues/1823.