F43 Change Proposal: Release of Greenboot Rust Rewrite (self-contained)

Wiki - https://fedoraproject.org/wiki/Changes/Greenboot_RS_Change_Proposal
Discussion thread -
https://discussion.fedoraproject.org/t/f43-change-proposal-release-of-greenboot-rust-rewrite-self-contained/160767

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.


== Summary ==
A rewrite of Greenboot written in Rust will be released, designed for
use with bootc and rpm-ostree based systems. This Greenboot release
will have the same functionality as the original Bash release, which
was only intended for rpm-ostree based systems.

== Owner ==
* Name: [[User:saypaul| Sayan Paul]]
* Email: saypaul@redhat.com
* Name: [[User:pwhalen| Paul Whalen]]
* Email: pwhalen@redhat.com
* Name: [[User:djachimo| David Jachimowicz]]
* Email: djachimo@redhat.com


== Detailed Description ==
As this release is a Rust rewrite of the Bash Greenboot version, the
functionality remains the same. It is detailed as follows:

Greenboot-RS exists to provide health check and rollback functionality
to bootc and rpm-ostree based systems. It allows a user to specify
health checks (scripts and binaries) to run every time the system
boots. These health checks can be either required or wanted, with the
difference of wanted checks not needing to succeed to allow a boot. If
any required checks fail the system will reboot, and may rollback to a
previous, working deployment if necessary.

Greenboot consists of two packages: `greenboot` and
`greenboot-default-health-checks`. The former, `greenboot` comprises
all the core functionalities of Greenboot. This includes checking
provided scripts and binaries, rebooting when required scripts or
binaries fail, and rolling back to a previous deployment if the
problem remains unsolved. The second package,
`greenboot-default-health-checks`, contains a series of optional
health checks curated and provided by the Greenboot maintainers.

A Greenboot execution begins on boot with
`greenboot-healthcheck.service`, which runs before systemd's
`boot-complete.target`. It launches `/usr/libexec/greenboot/greenboot
check`, which runs the `required.d` and `wanted.d` scripts.

If any script in `required.d` fails, greenboot run the scripts in the
`red.d` folder. Following this, a MOTD (Message of the Day) is created
specifying which scripts have failed. Checks are then performed to
determine if there's a need for manual intervention. If not, then the
system is rebooted.

If all scripts in `required.d` succeed:
* `boot-complete.target` is reached.
* The `boot_counter` GRUB env variable is unset and the `boot_success`
GRUB env variable is set to 1.
* Runs the scripts in the `green.d` folder. These are the scripts
intended to be run after a successful update.
* A MOTD with a success message is created.

== Feedback ==
Feedback from the community was positive regarding the Bash Greenboot
release, and it is now included with every Fedora IoT installation.
Various bugs and hiccups have been fixed as they have been found, and
those changes are included within this Rust rewrite. This section will
continue to be updated as more feedback is presented.

== Benefit to Fedora ==
This release is another step towards the adoption and support of bootc
systems with Fedora. Originally, the Greenboot release was written in
Bash and designed for use only with rpm-ostree based systems. This
change releases a new version of Greenboot, Greenboot-RS, written in
Rust and designed for usage with bootc and rpm-ostree based systems.
This change will allow users to utilize the advantages of a bootc
system, while still having the safety and reliability of Greenboot.

== Scope ==
* Proposal owners:
** Update with consolidation of services, such that all Greenboot
services have been collapsed into a single service.
** Update to allow seamless bootc upgrading. i.e. Upgrading from
Greenboot to Greenboot-RS using only `bootc upgrade`.

* Other developers: N/A

* Release engineering: [https://pagure.io/releng/issues #Releng issue
number] N/A

* Policies and guidelines: N/A (not needed for this Change)

* Trademark approval: N/A (not needed for this Change)

* Alignment with the Fedora Strategy: This change aligns with Fedora's
goal of increasing contributors, as it helps further the integration
of bootc and Fedora IoT.


== Upgrade/compatibility impact ==
Current IoT users will experience a seamless transition to this new
Greenboot release, using `rpm-ostree upgrade` to grab the new version.
This new release will retain all the functionality of previous
versions.


== Early Testing (Optional) ==
N/A

Do you require 'QA Blueprint' support? No <!-- Optional Step for
System-Wide Changes only -->

== How To Test ==
Once added to the Fedora IoT compose, you can test Greenboot-RS basic
functionality by logging in via SSH. You should be greeted by this
MOTD:

`Boot Status is GREEN - Health Check SUCCESS`

Ensure that the boot status and health check are both listed as above.


== User Experience ==
Current IoT Users should notice no changes, apart from their Greenboot
version iterating after `rpm-ostree upgrade`. All functionality from
previous Greenboot versions is retained, so the health check features
they are used to will still remain.

Future IoT Users leveraging bootc will notice Greenboot support
included when setting up IoT with bootc. These Users will now have
access to the health check and rollback features Greenboot provides,
and will start to see a Greenboot MOTD when booting their systems.

== Dependencies ==
N/A


== Contingency Plan ==
In the event of unexpected issues or setbacks with Greenboot-RS
implementation, we will rollback to the previous Bash Greenboot
implementation. As the release plan for Greenboot-RS involves creating
a separate Greenboot-RS package, rollback will be accomplished by
untagging the new Greenboot-RS package in Koji.

* Contingency mechanism: Users may uninstall the Greenboot-RS package
and the Bash Greenboot package will remain in service.
* Contingency deadline: 08-12-2025
* Blocks release? N/A (not a System Wide Change)

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

== Release Notes ==


--
Aoife Moloney

Fedora Operations Architect

Fedora Project

Matrix: @amoloney:fedora.im

IRC: amoloney

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