167 lines
7.1 KiB
HTML
167 lines
7.1 KiB
HTML
<article>
|
|
<h1>fedostree</h1>
|
|
<p>An instance
|
|
of <a href="https://github.com/cgwalters/rpm-ostree">rpm-ostree</a>
|
|
for Fedora. This project takes multiple RPM package sets from
|
|
Fedora, assembles them on the build server side, and stores these
|
|
trees in
|
|
an <a href="http://live.gnome.org/Projects/OSTree">OSTree</a>
|
|
repository. Client systems can them atomically upgrade and switch
|
|
between these trees.
|
|
</p>
|
|
<h3>Trying it out</h3>
|
|
<p>See <a href="#installation">installation</a>.</p>
|
|
<h3>Background</h3>
|
|
<p>Fedora today is an extremely flexible system. One can find
|
|
Fedora builds running on everything from hobbyist ARM devices,
|
|
to workstations, to testing servers.
|
|
</p>
|
|
<p>
|
|
This flexibility derives in large part from the fact that from a
|
|
technological point of view, Fedora is a collection of packages.
|
|
While pre-assembled "deliverables" such as the Live CDs are
|
|
distributed by the project, they are only a temporary state.
|
|
</p>
|
|
<p>
|
|
For example, as soon as they are installed, upgrading involves
|
|
having a package manager the dynamically reassemble the system
|
|
from newer parts in the Fedora package collection. One cannot
|
|
file a bug against the "default offering" as a whole - a package
|
|
must be chosen.
|
|
</p>
|
|
<p>
|
|
Furthermore, nearly every aspect of the Fedora infrastructure
|
|
(and documentation) is structured in terms of packages, from
|
|
user-facing tools such as Bugzilla and Bodhi, to developer tools
|
|
such as Koji. The announced security updates are based on package
|
|
names.
|
|
</p>
|
|
<p>
|
|
In contrast for example, ChromeOS is delivered and updated as an
|
|
pre-assembled atomic unit. ChromeOS is (compared to Fedora)
|
|
completely inflexible, but fulfills a targeted role clearly
|
|
well.
|
|
</p>
|
|
<h3>How OSTree allows a middle ground</h3>
|
|
<p>
|
|
Fundamentally, packages are partial filesystem trees with
|
|
metadata - they are assembled by a package manager into a complete
|
|
bootable tree. It's important to emphasize that it is only
|
|
these <emphasis>complete</emphasis> trees that users run.
|
|
</p>
|
|
<p>
|
|
OSTree allows an OS distributor to
|
|
ship <emphasis>multiple</emphasis> complete bootable filesystem
|
|
trees, and furthermore, client machines can atomically switch
|
|
between them, or even track multiple trees independently.
|
|
</p>
|
|
<p>
|
|
This allows a middle ground between the two extremes of a
|
|
combinatorial explosion of packages, and a singular OS.
|
|
</p>
|
|
<p>For example, these are some of the trees the current prototype generates:
|
|
<ul>
|
|
<li><tt>fedostree/20/x86_64/base/minimal</tt> - Just <tt>@core</tt>.</li>
|
|
<li><tt>fedostree/20/x86_64/server/docker-io</tt> - This tree contains <tt>@standard</tt> plus <tt>docker-io</tt>.</li>
|
|
<li><tt>fedostree/20/x86_64/server/freeipa-server</tt> - This tree contains <tt>@standard</tt> plus FreeIPA.</li>
|
|
<li><tt>fedostree/20/x86_64/workstation/gnome-core</tt> - The GNOME workstation with no applications.</li>
|
|
<li><tt>fedostree/20/x86_64/workstation/gnome-default</tt> - The above, with default applications.</li>
|
|
<li><tt>fedostree/20/x86_64/workstation/gnome-development-and-virt</tt>
|
|
- The above, with development tools, and virtualization client
|
|
and server side.</li>
|
|
</ul>
|
|
</p>
|
|
<h3>Initial goals</h3>
|
|
<p>
|
|
The first goal of this project is to be an <i>additional</i>
|
|
deployment option built in the Fedora infrastructure. In this
|
|
phase, developers and testers can use OSTree to replicate and
|
|
atomically transition between the pre-assembled trees produced by
|
|
this build server.
|
|
</p>
|
|
<p>
|
|
In this phase, no common mechanism for additional software
|
|
installation is provided. That said, individual trees can do so;
|
|
for example <tt>server/docker-io</tt> tree can use Docker to
|
|
install and run server container applications independent of
|
|
OSTree.
|
|
</p>
|
|
<p>
|
|
This phase does include basic integration testing on the build
|
|
server side, which will be a major benefit to the Fedora project
|
|
and its downstreams.
|
|
</p>
|
|
<h3>Required changes in Fedora/RPM for initial deployment</h3>
|
|
<p>
|
|
A change to
|
|
include <a href="https://sourceware.org/bugzilla/show_bug.cgi?id=16142">/usr/lib/passwd</a>
|
|
is required; this is implemented currently by
|
|
the <tt>nss-altfiles</tt> package. See
|
|
also <a href="http://fedorapeople.org/~walters/Use-usr-lib-passwd-for-system-users-if-it-exists.patch">this
|
|
patch</a> for shadow-utils.
|
|
</p>
|
|
<p>
|
|
All RPMs should stop shipping files and directories
|
|
in <tt>/var</tt>.
|
|
See <a href="https://people.gnome.org/~walters/ostree/doc/layout.html">this
|
|
section</a> of the OSTree documentation.
|
|
</p>
|
|
<p>
|
|
RPM should cope with its database living
|
|
in <tt>/usr/share/rpm</tt> and being immutable.
|
|
</p>
|
|
<h3>Development area: OSTree Layering</h3>
|
|
<p>
|
|
This phase would be allowing "layering" of trees. For example,
|
|
if one installs the <tt>base/minimal</tt> tree, one could imagine
|
|
taking the <tt>strace</tt> package, and computing a new
|
|
filesystem tree which is the union of the two.
|
|
</p>
|
|
<p>
|
|
While plain standalone ELF executables would work with no
|
|
modification, a generalization of this kind of dynamic layering
|
|
implies a higher level above OSTree that is aware of things
|
|
like <tt>ldconfig</tt> and <tt>gtk-update-icon-cache</tt> and how
|
|
to trigger them when layers are combined
|
|
</p>
|
|
<p>
|
|
Conceptually, this is a step back towards combinatorics. For example,
|
|
if libvirt is a layer that could be applied on top of the base server
|
|
layer as well as the workstation layer, then there would need to be
|
|
some notion of dependencies.
|
|
</p>
|
|
<h3>Development area: Local package assembly</h3>
|
|
<p>
|
|
There is absolutely no reason one could not just use the package
|
|
manager on the client side to download and assemble packages -
|
|
but rather than operating live on your current root, OSTree
|
|
allows setting up the chosen tree for the next boot
|
|
atomically.
|
|
</p>
|
|
<p>
|
|
The problem is making this sort of thing efficient and scalable;
|
|
it would require careful integration of the local OSTree repository
|
|
and the package manager caching to operate at a speed comparable to
|
|
traditional package management.
|
|
</p>
|
|
<h3>Development area: Live updates</h3>
|
|
<p>
|
|
If one is using OSTree in a model without a separate application
|
|
mechanism (as is the case for rpm-ostree), it is potentially
|
|
painful to reboot just to upgrade applications.
|
|
</p>
|
|
<p>
|
|
It would be quite easy to do a bind mount of the new /usr over
|
|
top of the old. This would avoid some of the problems dpkg/rpm
|
|
have in creating an <emphasis>partial</emphasis> view. But even
|
|
this model would still break many real world desktop applications
|
|
such as Firefox. Few applications handle files from an arbitrary
|
|
new version replacing their current ones.
|
|
</p>
|
|
<p>
|
|
Starting from an <emphasis>safe</emphasis> basis, it should be
|
|
possible to engineer userspace so that many classes of upgrades
|
|
can be applied both live and safely, without race conditions.
|
|
</p>
|
|
</article>
|