This is the second part of https://github.com/openshift/enhancements/pull/1637 and https://issues.redhat.com/browse/OCPSTRAT-1190. The first part consisted of building the OCP node image as a layered image on top of RHCOS. Now, we do the next split, which is to make RHCOS itself a layered image on top of rhel-bootc.

Success: Being able to build CoreOS using podman build, as part of this epic we do not touch the disk images build steps, this targets only the CoreOS bootable container image.

Risks:

• We have only one 9.6 base image, so changes going in 4.20 will also go to 4.19. First we can target C9s and C10s
• RHCOS will now be composed of the RHEL rpm-ostree version, not Fedora anymore.

Dependencies: → bootc features needing to be backported to 9.6?

Tasks Breakdown:

• Spike: test building FCOS on top of fedora-bootc using the custom base image flow
• Support “importing” container builds into cosa
  • Right now, cmd-build does an rpm-ostree compose
  • This needs to change to do a podman build and import it
  • cmd-build could be the place to do change detection.
• Hook up dependency bot to bump rhel-bootc digest pullspec in coreos/fedora-coreos-config and coreos/rhel-coreos-config.
  • Update FROM line. In FCOS, it can be all the time, in RHCOS we want to bump only if the manifests changed ideally. See discussions in https://github.com/coreos/fedora-coreos-tracker/issues/1861.

Not doing:

• We don’t look at packaging the ignition bits that are currently not package

Testing:

• Probably no impact, but we benefit from RHEL and Fedora Image Mode testing.

References:

• RHEL Image mode integration in RHEL composes: https://issues.redhat.com/browse/RHELCMP-14502
• Fedora bootc in Fedora composes: https://pagure.io/releng/issue/12731
• https://docs.fedoraproject.org/en-US/bootc/building-custom-base/
• https://github.com/coreos/fedora-coreos-tracker/issues/1861