https://fedoraproject.org/wiki/Changes/FlatpaksWithoutModules
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.
== Owner ==
* Name: [[User:Otaylor|Owen Taylor]]
* Email: otay...@redhat.com
== Detailed Description ==
There are two types of Flatpak containers -
runtimes - which contain unmodified Fedora packages,
and applications - which contain Fedora packages rebuilt to relocate
them from /usr to /app.
Currently, the rebuild process is done using modules -
packages are either rebuilt in a shared flatpak-common module, or in a
module specific to the application.
This change replaces this with a separate build target that all
rebuilds are done in.
=== Rebuilding RPMs ===
For each Fedora release, we'll have two additional targets
f39-flatpak-runtime (inherits f39), tags: f39-flatpak-runtime-build,
f39-flatpak-runtime
f39-app (inherits f39-flatpak-runtime), tags: f39-app-build, f39-app
The f39-flatpak-runtime target has a limited use -
it's used to build packages that go into the Flatpak runtimes
(standard and KDE).
This would include flatpak-runtime-config, flatpak-rpm-macros,
but also rebuilds of standard packages if needed to prune dependencies:
currently this is done for gstreamer-plugins-good.
The f39-app target is the main target that is used for prefix=/app rebuilds.
flatpak-rpm-macros is part of the build group for this target,
resulting in builds that target /app.
As currently, spec files can be conditionalized with '%if 0%{?flatpak}'
Builds in f39-flatpak-runtime and f39-app have the dist tags
.f39runtime and .f39app respectively.
This is necessary so that we can automatically rebuild a package
without having to bump the release in the specfile.
(Koji requires everything to have a unique NVR.)
It also allows humans and tools to easily distinguish these specialized builds.
Any Fedora packager can rebuild a package into f39-app using 'fepdkg
build --target=f39-app'.
There will also be a new convenience subcommands of fedpkg 'fedpkg
build-flatpak-rpms',
'fedpkg build-flatpak-rpms-local' that can be used to rebuild all
missing bundled dependencies of a Flatpak,
in Koji or locally.
Once a package exists in f39-app or f38-app, then
[[https://gitlab.com/redhat/centos-stream/ci-cd/distrosync/distrobuildsync
distrobuildsync]] will be used to do a build into f39-app each time a
standard build completes.
=== Container Versioning ===
Currently, the version is based on the module version:
firefox:stable:3820230427145713:b1edb643 =>
firefox-stable-3820230427145713.b1edb643
Where the module version is created from platform versions and git
commit timestamps
for the module repository.
We could reproduce something very much like this based on the runtime branch and
git commit timestamp, but since application Flatpaks have an
identifiable "Main RPM"
(unlike the general case of modules and containers), a better scheme is:
firefox-112.0.2-1.fc38 => firefox-flatpak-112.0.2-1
name: main RPM name + -flatpak
version: main RPM version
release: automatically incremented based on existing Koji builds
Because upgrades are done on Flatpak ID (org.mozilla.Firefox),
there is no compatibility impact of switching Flatpaks from 'firefox'
to 'firefox-flatpak'.
There is considerable implementation complexity within OSBS to implement this,
because the N/V/R need to be written into generated Dockerfile as
labels ''before'' building it,
but it should be manageable. If not, we'll need to switch to a different scheme.
(Running dnf with <code>--best</code> when building the container will
help make this reliable
and would be a general improvement.)
=== Updates ===
The current plan is that builds of RPMs will be tagged directly into f39-app and
containers will be composed from the contents of f39-app with no
involvement of Bodhi.
Bodhi is only involved in releasing the container.
We can add CI checks on container updates to compare the rebuilt
packages in the container
to the latest released versions for Fedora, though it's not always
easy to distinguish:
* Newer because of a RPM change that hasn't passed testing yet
* vs. Newer because a spec file was needed to get the package to
rebuild with prefix=/app
Since Fedora does not embargo builds,
there's no potential information leak if a change to dist-git is
released via container before it is released by RPM.
=== Disadvantages and issues===
In moving to this system, we lose the ability to take advantage of the
capabilities of modularity -
to use a different stream branch of a library for an application than
the one shipped in F39, say.
There are essentially no examples of this being used in all the
Flatpaks created for Fedora over the last 5 years,
probably because modularity has gained little traction within Fedora
more broadly.
Some Flatpak modules strip down bundled packages by setting macros in
the buildopts/rpms/macros section of the
modulemd file. For example, flatpak-common has:
buildopts:
rpms:
macros: |
%_without_mingw 1
%_without_tkinter 1
This is no longer possible, so these changes need to be fed back into
spec files with
'%if 0%{?flatpak}' style conditionalization.
Additionally a couple of packages (evolution-data-services and
tracker-miners) are set up so they can be
built with an application-specific D-Bus prefix. Evolution has:
buildopts:
rpms:
macros: |
%_eds_dbus_services_prefix org.gnome.Evolution
This will need to be redone so that evolution-data-services doesn't
need recompilation
and the prefixing can be done by changing configuration files at
container build time.
== Feedback ==
== Benefit to Fedora ==
The experience for Fedora developers who want to create Flatpaks of
their applications will be improved:
* They no longer need to understand modularity and modulemd files -
instead of a modulemd file *and* a container.yaml, they simply create
a container.yaml.
* Rebuilds are automatically shared between Flatpaks, without having
to get them added to the flatpak-common module.
* Because the local build experience is no longer using the poorly
maintained local-build mode of MBS, it can be more efficient and
easier to understand.
This should result in more Fedora Flatpaks and more up-to-date Fedora Flatpaks.
We also greatly reduce the usage of Module Build Service within Fedora.
This is important because upstream maintenance is currently reduced,
and it's not clear that we'll be able to sustain a deployment indefinitely.
== Scope ==
* Proposal owners:
** Update flatpak-module-tools to be able to work without modularity
** Create changes to fedpkg to add 'rebuild-flatpak-packages'
(implementation likely within flatpak-module-tools)
** Update atomic-reactor to be able to build Flatpaks without modularity
* Other developers:
** Flatpaks will need to be migrated to the new system by Flatpak
packagers. While we could make the new system opt-in for F39, it's
probably easiest to just require all Flatpaks to be moved over. In
many cases, this should consist of just a few minor changes to
container.yaml.
** Changes to fedpkg and atomic-reactor need to be reviewed, and for
atomic-reactor deployed. '''Note''' Fedora is on OSBS 1, which is not
a current release. Backporting changes to OSBS 1 seems more realistic
than upgrading Fedora to OSBS 2 at this point.
* Release engineering: [https://pagure.io/releng/issue/11415 #Releng
issue number]
** Release engineering will need to manually create the tags/targets
for F39 and update the tag maintenance scripts to do this for future
releases.
* Policies and guidelines:
https://docs.fedoraproject.org/en-US/flatpak/ will need to be updated
once we have an initial implementation. No impact to packaging
guidelines is expected.
* Trademark approval: N/A (not needed for this Change)
* Alignment with Community Initiatives: No
== Upgrade/compatibility impact ==
The Flatpaks built will look exactly the same as before from a user perspective.
== How To Test ==
Testing here will be done by selecting a few Flatpaks and trying to
rebuild them using the new system,
first locally and then on infrastructure.
The final validation will be when we mass rebuild Flatpaks for F39.
== User Experience ==
This should be largely invisible to users.
Hopefully, by simplifying the developer experience around creating Flatpaks,
more Fedora Flatpaks will be available and they will be kept more up-to-date.
== Dependencies ==
This is unrelated to other Fedora changes or to changes within packages.
== Contingency Plan ==
* Contingency mechanism: The current infrastructure for module-based
builds will be maintained, so that if we can't get this done for F39,
we'll build Flatpaks as modules for F39.
* Contingency deadline: By 2023-08-01 we should have runtimes built
and a number of applications or we'll plan on using modules for F39
Flatpaks.
* Blocks release? No
== Documentation ==
At the moment, this change proposal is standalone documentation of the
change. As noted above, https://docs.fedoraproject.org/en-US/flatpak/
will need to be updated once we have an initial implementation. If you
are interested in getting involved in planning and implementing this
change, please contact the
[https://fedoraproject.org/wiki/SIGs/Flatpak Flatpak SIG] matrix room.
== Release Notes ==
--
Aoife Moloney
Product Owner
Community Platform Engineering Team
Red Hat EMEA
Communications House
Cork Road
Waterford
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