Fedora 32 System-Wide Change proposal: Restart services at end of rpm transaction

[Ben Cotton]

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

== Summary ==

Scriptlets to restart each service that should be restarted in each
rpm package will be replaced by a declaration in the unit file and an
rpm transaction trigger that fires at the end and restarts all
services.

== Owner ==
* Name: [[User:zbyszek| Zbigniew Jędrzejewski-Szmek]]
* Email: zbyszek at in waw pl


== Detailed Description ==

Currently, when packages containing systemd services are upgraded,
they are restarted through %post scriptlets in each package. In other
words, the scriptlets specify which services should be restarted and
actually run the command to restart the service. An alternative
mechanism will be provided, whereby the unit file contains a setting
which specifies that the service should be restarted on upgrade, and a
%transfiletrigger in the systemd package will restart all services
marked so in upgraded packages at the end of transaction.

To mark a services as "restart on upgrade" the unit file should
contain an option to mark it so. This can be either in the main
.service file, or e.g. in a drop-in file in
<code>/usr/lib/systemd/system/<service>.service.d/needs-restart.conf</code>.
The exact name of the option should be something like
<code>X-restart-on-upgrade=true|false</code>. I'll take the proposal
for discussion in systemd upstream, since this is something that could
be used across distributions, and then the "X-" prefix could be
dropped and/or the name changed.

== Benefit to Fedora ==

Which services should be restarted is specified declaratively and the
number of scriptlets is reduced.

Admins may easily override this by providing appropriate drop-ins of
their own of higher priority.

Services are restarted after the transaction is finished, all
libraries have been upgraded, and systemd configuration reloaded. This
solves https://bugzilla.redhat.com/show_bug.cgi?id=1614751, but also a
more general problem: a service may be restarted before any of its
dependencies (files and static content and whatnot) have been
upgraded, and while some contents from the old rpm are still on disk.
Restarting after all packages have been upgraded avoids this issue.

In the future, restarting of services shall also be extended to user
managers (i.e. to restart all user services after the packages
providing those services have been upgraded). This is not part of this
proposal, but moving the information what to restart into systemd
units makes this much easier.

== Scope ==
* Proposal owners:
** implement the relevant bits in the systemd package
** submit a proposal to FPC
** convert a subset of packages

* Other developers:
** FPC: review (and accept ;)) the guidelines changes
** other maintainers: convert other packages

* Release engineering: n/a

* Policies and guidelines: a pull request will be submitted

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

== Upgrade/compatibility impact ==
This change should be backwards compatible, i.e. unconverted packages
can be still installed on new systems, and services will be restarted
on upgrade like before. Converted packages may be installed on older
systems but will not get restarted on upgrades.

== How To Test ==
This change should be mostly invisible to users. Check that during
upgrades services are restarted and that no warnings are emitted.

== User Experience ==
N/A

== Dependencies ==
N/A

== Contingency Plan ==

* Contingency mechanism: Revert to previous mechanism. This will
require a revert of changes to the spec file and a rebuild of the
package.

* Contingency deadline: beta freeze
* Blocks release? No
* Blocks product? No

== Documentation ==
TBD.

== Release Notes ==
Not needed.

-- 
Ben Cotton
He / Him / His
Fedora Program Manager
Red Hat
TZ=America/Indiana/Indianapolis