F40 Change Proposal: Build Fedora IoT using rpm-ostree unified core (Self-Contained)

[Aoife Moloney]

Wiki -> https://fedoraproject.org/wiki/Changes/Fedora_IoT_Unified_Core

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes
process, proposals are publicly announced in order to receive
community feedback. This proposal will only be implemented if approved
by the Fedora Engineering Steering Committee.

= Build Fedora IoT using rpm-ostree unified core =

== Summary ==
Upstream rpm-ostree development is now focused on "unified core" mode,
with plans to deprecate the previous mode in the future. Fedora IoT is
the last rpm-ostree based Fedora edition using this older, soon to be
deprecated mode with SilverBlue and Kinoite making the change in
Fedora 39. This change will align IoT with the other ostree-based
editions in Fedora.

== Owner ==
* Name: [[User:pwhalen| Paul Whalen]], [[User:idiez| Irene Diez]]
* Email: [e-mail], [e-mail]

== Detailed Description ==
To learn about the differences between unified core and the previous
mode, please read the upstream
[https://github.com/coreos/rpm-ostree/issues/729 issue]. The main
advantage is that it is stricter and safer, while enabling some post
processing steps to happen during or after the image build. In
addition, unified core support is required for bootupd integration in
Fedora IoT and to align with other rpm-ostree editions in Fedora.

Related changes (already complete):

* https://fedoraproject.org/wiki/Changes/FedoraSilverblueUnifiedCore
* https://fedoraproject.org/wiki/Changes/FedoraSilverblueBootupd

== Feedback ==

== Benefit to Fedora ==
The previous mode in rpm-ostree is not maintained anymore, less tested
and thus prone to bugs. Moving to unified core will align IoT with
what is used to build Fedora CoreOS, SilverBlue and Kinoite as well as
benefit from the additional testing those editions receive. Making the
change in IoT should also reduce the maintenance burden from the
rpm-ostree project as they will be able to remove the old code.
Unified core makes composes work the same on the server side as the
client side and makes them safer by more strictly confining scriptlet
execution.

== Scope ==
* Proposal owners: Testing with the new mode to ensure there are no regressions.
* Other developers: N/A
* Release engineering: [https://pagure.io/releng/issue/11815 #11815]
* Policies and guidelines: N/A (not needed for this Change)
* Trademark approval: N/A
* Alignment with Community Initiatives: N/A

== Upgrade/compatibility impact ==
* There will be no impact to end users, upgrades will work the same as
previous releases

== How To Test ==
* Upgrade to Fedora 40 IoT Edition or deploy a new installation.

== User Experience ==
* There will be no impact to users.

== Dependencies ==
N/A

== Contingency Plan ==
* Contingency mechanism: Revert to older non-unified core mode.
* Contingency deadline: N/A (not a System Wide Change)
* Blocks release? N/A (not a System Wide Change)

== Documentation ==
N/A (not a System Wide Change)

== Release Notes ==
N/A