coordinating default hostname with other Fedora editions

[dustymabe]

Back in Fedora 33 the default hostname in the Fedora ecosystem was changed to fedora from localhost. The default hostname is the hostname that gets set when no hostname information can be found from any other source:

• set manually
• DHCP
• reverse DNS lookup

At the time we decided to freeze on systemd with the fallback hostname change reverted and then later (once the feature was added) we unfroze systemd and started setting the DEFAULT_HOSTNAME in /etc/os-release to localhost.

Now (f35+) we are at a point where NetworkManager has fixed upstream to handle rDNS cases properly and Fedora CoreOS itself no longer needs the DEFAULT_HOSTNAME to be set to localhost, but maybe our users scripts/configuration/automation do need it still.

Depending on the answer to that question our options include:

0. remove the DEFAULT_HOSTNAME=localhost entry, default hostname reverts to fedora
1. keep this DEFAULT_HOSTNAME=localhost delta forever only in FCOS (not ideal)
2. convince a subset of Fedora editions to change (non workstation use cases)
3. convince the entirety of Fedora editions to change (not likely)

It was suggested by @jlebon that we go for 2., which I would assume we'd need to try to talk to FESCO about.

[jlebon]

Previous discussions on this subject with other maintainers in https://bugzilla.redhat.com/show_bug.cgi?id=1892235.

[dustymabe]

We discussed this in the meeting today.

2021-07-21 13:24:34  dustymabe  #agreed we start a discussion with FESCO about potentially updating
                                the default hostname to be localhost for server like editions. If that
                                is rejected then we re-visit if we want to carry the delta just in FCOS
                                or not.

[dustymabe]

After talking with bcotton about it I'm going to discuss this with the other Editions/Working Groups that we think would find this useful first to do some temperature taking. On the list:

• Fedora IoT
• Fedora Cloud
• Fedora Server

[dustymabe]

Here's my pitch to the other working groups:

---

Back in Fedora 33 the default hostname was changed from localhost to fedora on instances that didn't get the hostname set in any other way (i.e. it's the fallback if it's not set anywhere else). As far as I know this change came in in systemd and was never proposed as a change in Fedora itself.

Here's the original enablement upstream systemd/systemd#5175 and the BZ requesting the change in Fedora: https://bugzilla.redhat.com/show_bug.cgi?id=1392925

Unfortunately, this initiallly caused us in FCOS some pain because setting the hostname via reverse DNS lookups (via NetworkManager) stopped working along with breaking 3rd party tools that set the hostname. The NM problem was subsequently fixed, but it still remains that a lot of third party software will check to see if an instance's hostname is "unset" by checking the current hostname against the string "localhost". Additionally it even seems that this change will never be picked up by CentOS/RHEL (see https://src.fedoraproject.org/rpms/systemd/c/13d1341b108a24d13f5922054307b5c2efc6836a?branch=rawhide).

The open question is, what do we think the fallback hostname should be for server like instances? And.. Should we do anything to change it for a subset of Editions/Working Groups in Fedora?

[dustymabe]

Talked with the IoT working group today and they seemed receptive and willing to work together on the change. I opened https://pagure.io/fedora-iot/issue/49 with all details and to raise awareness among any interested parties that weren't at the meeting.

[dustymabe]

Talked with the Cloud working group today. Opened https://pagure.io/cloud-sig/issue/376