F38 proposal: Ostree Native Container (Phase 2, stable) (System-Wide Change proposal)

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/OstreeNativeContainerStable

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 ==

Continue the work done in
https://fedoraproject.org/wiki/Changes/OstreeNativeContainer but in an
officially stable format, and expanded to cover more OSTree-based
editions.  This goes "all in" on being container-native and
significantly changes the technology and user emphasis.

== Owner ==

* Name: [[User:walters| Colin Walters]], [[User:jmarrero| Joseph
Marrero]], [[User:baude| Brent Baude]]
* Email: [e-mail], [e-mail], [e-mail]

== Detailed Description ==

* rpm-ostree's functionality to
[https://coreos.github.io/rpm-ostree/container/ boot and upgrade from
Docker/OCI container images] is declared stable
* Rework Fedora editions and spins (CoreOS, IoT, Silverblue, Kinoite,
etc) that use ostree to instead deliver via Docker/OCI container
images
* `rpm-ostree` is reworked to gain strong CLI compatibility with
`yum/dnf` commands (cliwrap)
* The new container native functionality is exposed via `dnf image`
* (TBD: Rebranding of rpm-ostree itself to `dnf-image` or something else)
* Support and documentation for generating derived images
* Support in Anaconda and other tools
* Support for generating bootable images

A top level goal is that users should not need to know or understand
ostree (or rpm-ostree); they only need to know containers and most key
functionality is exposed via the `yum/dnf` frontend with a few
extensions.

=== Backwards compatibility ===

If you're a user of ostree today: no need to worry.  Everything that
works today in ostree and rpm-ostree will continue to work for years
to come (it's shipped in RHEL9). However, it's expected that most
users will find the new model sufficiently compelling to switch fairly
quickly.

=== Stable Bootable OCI ===

More information about this is available in
[https://coreos.github.io/rpm-ostree/container/ the rpm-ostree
documentation].  This Change highlights that this functionality is
planned to be officially stable.

=== Changing to OCI over the wire ===

Today Fedora has an OSTree repository that contains updates for
editions such as Fedora CoreOS and Fedora Silverblue.

These editions instead will become [https://github.com/opencontainers
OCI base images], available at e.g.

* `quay.io/fedora/fedora-coreos:stable`
([https://quay.io/repository/fedora/fedora-coreos this exists today]!)
* `quay.io/fedora/fedora-silverblue:38` (does not exist, but can soon)

An update will be shipped that will cause existing systems tracking
the production ostree branches to be switched to the corresponding
container image.  Concretely for example, a system running
`fedora:fedora/36/x86_64/silverblue` will execute `rpm-ostree rebase
ostree-remote-registry:fedora:quay.io/fedora/fedora-silverblue:36`.

Note that at the current time, Fedora does not sign container images.
This should change (likely to something based on
[cosign](https://github.com/containers/skopeo/pull/1701)), but in the
mean time, the ostree-container flow supports verifying the embedded
ostree-baesd GPG signatures and this will continue to be used.

The Fedora OSTree repository will become read-only and stop receiving updates.

Note that for Fedora CoreOS specifically, there is some outstanding
design discussion around the intersection with Cincinnati:
https://github.com/coreos/fedora-coreos-tracker/issues/1263

==== Wire efficiency ====

Today the container images generated by rpm-ostree are "chunked" in a
reproducible fashion; for more information on this, see

* https://github.com/ostreedev/ostree-rs-ext/issues/69
* https://coreos.github.io/rpm-ostree/container/

However, longer term (as that first issue notes) we do want to add
[https://github.com/containers/image/pull/902 container deltas].
Doing so will benefit non-host containers too.

=== dnf/yum CLI compatibility ===

rpm-ostree has a feature called
[cliwrap](https://coreos.github.io/rpm-ostree/cliwrap/) today.  A key
motivation here is that in the switch to using containers as the
frontend, the project name "rpm-ostree" (which is very literal) no
longer makes sense.  A further emphasis on "container native" will
strongly encourage writing e.g. a `Dockerfile` like this:

<pre>
FROM quay.io/fedora/fedora-silverblue:stable
RUN dnf -y install sway && ostree container commit
</pre>

*Today*, one can spell this as `RUN rpm-ostree install -y sway &&
ostree container commit` - but a toplevel goal here is to allow host
system customization using the same patterns and tools one uses to
build application containers, and to de-emphasize the "ostree backend"
aspect.

To complete this story on the client side, what is today called
"ostree native containers" will be exposed via a new `dnf image`
subcommand on the client system.

For example:

<pre>
$ dnf image rebase quay.io/examplecorp/customos:latest
</pre>

As well as other offline/"image based" functionality such as `dnf
image rollback` and `dnf image apply-live`.

However, as many people know, rpm-ostree does today support
"per-machine" package layering/overrides - and *that will continue to
work*.  So users are not *required* to do builds on a remote server
even in "image mode".

Concretely, it will also work to `sudo dnf -y install sway` inside a
root terminal on a Fedora Workstation for example.  This will still be
a transactional operation.

More: https://github.com/coreos/rpm-ostree/issues/2883

=== Rebranding of rpm-ostree ===

This is a fundamental change in technology *and* positioning for
rpm-ostree (and for the projects that use it).  The terminology of
"immutable" gets even fuzzier now (see also [this
blog](https://blog.verbum.org/2020/08/22/immutable-%E2%86%92-reprovisionable-anti-...)).

It would make sense to rebrand the project due to this.  No decision
has been made on this, but the choices are:

- Keep as is
- Rebrand to dnf-image (or, reviving a past name, yum-image)
- Rebrand to something else

More: https://github.com/coreos/rpm-ostree/issues/405

=== Support for building derivative containers ===

Until now, the model for systems like Fedora CoreOS and Silverblue
etc. has included an emphasis on containerization, but avoiding
extensive customization of the host system.  This will be weakened
somewhat - it will be fully supported to build derivative operating
system  images that in turn contain software which itself should run
directly on the host system, and not in a container.

A key aspect of this is that by generating a custom build, one binds
together the code and configuration as a transactionally updatable
unit.

The role of things like Kickstart, cloud-init, and Ignition and other
system config management shrinks significantly.

=== Example 1: Kubernetes and kubelet ===

It is not supported upstream to run the kubelet in a container image
itself.  Today, for OpenShift 4 we embed the kubelet as part of the
CoreOS builds.  The [https://www.okd.io/ OKD] project
[https://github.com/openshift/okd-machine-os/blob/fa2248d332abc9926e68428dc66...
already installs kubelet during a container build] deriving from the
base `fedora-coreos` image.  It is possible that RHEL CoreOS will make
[https://github.com/openshift/os/issues/799 a similar split].

=== Example 2: Agent software ===

Many organizations require agents (cloud agents, security scanners,
antivirus) which are not ready to be containerized.  Often too, these
tools come in e.g. RPM form, and also expect to be configured (remote
logging server, etc.).  This tooling allows to `dnf install` these
*and* embed the configuration, generating a standard container image
which can then be booted as an atomic unit.

(Note that in the OpenShift context, we expect this to chain with the
first example - users instead derive from a `okd-node-base` image
which itself derives from `fedora-coreos`).

=== Example 3: Podman machine ===

The `[http://podman.io Podman]` project has a function called
`[https://github.com/containers/podman/blob/main/docs/source/markdown/podman-m...
machine]` where it creates a virtual machine and boots standard CoreOS
builds. Podman developers and users has long desired a custom FCOS
image that is focused on container deployment using Podman, including
certain QEMU packages that allow for cross-architecture development.
This approach will solve a series of problems including but not
limited to getting more timely release alignment between Podman and
FCOS.

We also have a user base that wants to customize the VM image based on
restrictive environments ... bring your own virtual machine image.

=== Support in Anaconda and other tools ===

Anaconda support for custom images is tracked in this bug:
https://bugzilla.redhat.com/show_bug.cgi?id=2125655

But, as part of this Change, it should also work to generate an
Anaconda ISO which allows *user choice* for whether to install in
"image mode" or "traditional".

=== Support for generating bootable images ===

Instead of using an existing disk image/ISO (Anaconda, AWS AMI, etc.)
and then doing an in-place update to a generated container image, in
many cases will want to generate disk images using their container
image as input.

For example, generating an ISO that embeds that container image as
input and will install it.

In this proposal, we plan to ship a container image as part of Fedora
CoreOS that will do this:
https://github.com/coreos/fedora-coreos-tracker/issues/1151

But, it also makes sense to have a tool that e.g. does this and
generates an Anaconda ISO (we will inherently be doing this as part of
generating ostree-based Anaconda ISOs already!) - this would just be
supporting that in a clear external way too.  One likely target for
this is [https://github.com/osbuild osbuild] and
[https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/9/htm...
RHEL Image Builder].

== Feedback ==

== Benefit to Fedora ==

The need to understand ostree goes away for most users; they
understand RPMs and containers.  While retaining all the current
(rpm-)ostree features.

== Scope ==
* Proposal owners:
* Other developers: May affect e.g. gnome-software and similar tools
that talk to rpm-ostree.

* Release engineering: [https://pagure.io/releng/issue/11047]
* Policies and guidelines: None.
* Trademark approval: N/A (not needed for this Change)
* Alignment with Objectives: None

== Upgrade/compatibility impact ==

We will ship a systemd unit that transitions systems currently using
OSTree on the wire over to tracking the corresponding container
images.  Note again, all features of rpm-ostree continue to work!  For
example, if you have layered packages, that will continue to be
applied.

== How To Test ==

Build container images, boot them.

== User Experience ==

Users will not need to understand ostree (at least at a superficial
level), only container images.

== Dependencies ==

Needs improvements in Anaconda in some cases, also would like to
increase alignment with dnf.  Fetching container images uses `skopeo`,
maintained by containers team.

== Contingency Plan ==
* Contingency mechanism: Continue to ship things the way we ship them today
* Contingency deadline: Dunno
* Blocks release? No

== Documentation ==

https://coreos.github.io/rpm-ostree/container/ and
https://github.com/coreos/coreos-layering-examples etc.

== Release Notes ==