F43 Change Proposal: Use update-alternatives for managing NodeJS symlinks (self contained)

Wiki - https://fedoraproject.org/wiki/Changes/NodejsAlternativesSystem
Discussion thread -
https://discussion.fedoraproject.org/t/f43-change-proposal-use-update-alternatives-for-managing-nodejs-symlinks-self-contained/158042/2


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 ==

We aim to move away from manual management of
<code>/usr/bin/node</code>, <code>/usr/bin/npm</code>, and similar
symlinks to leveraging update-alternatives system.

== Owners ==

* Name: [[User:aradchen|Andrei Radchenko]]

* Email: aradchen@redhat.com


* Name: [[User:jstanek|Jan Stanek]]
* Email: jstanek@redhat.com

* Name: [[User:tjuhasz|Tomas Juhasz]]
* Email: tjuhasz@redhat.com



== Detailed Description ==

This is a part of a larger iteration in a way we package NodeJS for
Fedora and RHEL. The other parts are [[Changes/NodejsNodeModulesPath]]
and [[Changes/NodeJSMetapackages]].
This change deals specifically with the management of the
non-versioned symlinks in system paths.

Currently, the NodeJS packages (streams) provided in Fedora are all
installable in parallel,
by virtue of moving any potentially conflicting bits into versioned
equivalents and/or versioned directories.
For one example of many:

<pre>
%install
mv %{buildroot}%{_bindir}/node %{buildroot}%{_bindir}/node-%{node_version_major}
...
</pre>

One of the streams is designed as the "default" one, and that stream
then ships manually created non-versioned symlinks to the renamed
paths:

<pre>
%if 0%{nodejs_is_default}
ln -srf %{buildroot}%{_bindir}/node-%{node_version_major}
%{buildroot}%{_bindir}/node
...
%endif
</pre>

By using update-alternatives, we can iterate on this idea and gain
several benefits outlined below.

== Feedback ==

== Benefit to Fedora ==
# No matter which stream you install, you'll always have
<code>/usr/bin/node</code> and other non-versioned names available.
The versioned names will be also present, if you want to be specific
in your scripts.
# There is no "official Fedora endorsement" on which NodeJS stream
should be "best" or "default"; if you as a system administrator have
multiple streams installed, the decision of which should be the
default is up to you.

The second item will also give us the maintainers greater freedom in
introducing new streams and obsoleting the old ones without worrying
too much about how to switch the "default" in the middle of the
distribution life cycle.
This is not a big pain point for Fedora, where the length of the life
of a single version matches the length of upstream NodeJS LTO support
pretty closely,
but becomes much more important in longer-living downstream
distributions (e.g. RHEL).

== Scope ==
* Proposal owners:
** Port the manual symlink creation and management to update-alternatives.
** Ensure the streams behave consistently and no conflict is introduced.


== User Experience ==
* Users will be able to install any number of streams and switch
between default one rather easy by just running `update-alternatives
--config node'.

== Dependencies ==
* Should not cause any problems to dependant packages.


== Contingency Plan ==
* Contingency mechanism: Revert back to manual symlink management and
go back to the design phase.
* Contingency deadline: Beta Freeze.
* Blocks release? We aim to do the rebuilds in Koji side tag and merge
it atomically; so NO.


== Documentation ==
* This is a downstream change; this page is the initial documentation.
* [https://docs.fedoraproject.org/en-US/packaging-guidelines/Alternatives/
Fedora Alternatives]

== Release Notes ==
TODO

--
Aoife Moloney

Fedora Operations Architect

Fedora Project

Matrix: @amoloney:fedora.im

IRC: amoloney

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