cloud-init non FQDN hostname not working as expected on AlmaLinux

[kovalroma]

Bug report

The configuration of non-Fully Qualified Domain Name (FQDN) hostnames seems to be encountering issues on AlmaLinux and other distributions based on RHEL8, such as Rocky Linux and CentOS 8.

When setting up a hostname like almalinux.lan, cloud-init successfully configures the system hostname. However, when using a non-FQDN hostname like almalinux, cloud-init fails to configure it properly, leaving the hostname as localhost.

Steps to reproduce the problem

1. AlmaLinux image created with Packer utility on Proxmox, latest version of cloud-init installed from repo with command dnf install cloud-init -y
2. In Proxmox right click on created image, selected Clone image.
3. In new window setup Name and click Clone
4. Proxmox created Cloud-init disk with name cidata with following content of user-data
5. Started Linux

What I understand is that user-data is different. In case of almalinux.lan, fqdn key in user-data was created by Proxmox. Hostname was correctly set up . In case of almalinux, no fqdn key in user-data was created by Proxmox. Hostname was not correctly set up .

user-data of almalinux.lan

#cloud-config
hostname: almalinux
manage_etc_hosts: true
fqdn: almalinux.lan
chpasswd:
  expire: False
users:
  - default
package_upgrade: true

user-data of almalinux

#cloud-config
hostname: almalinux
manage_etc_hosts: true
chpasswd:
  expire: False
users:
  - default
package_upgrade: true

Later I checked image created for Ubuntu with non FQDN hostname. In case of ubuntu, no fqdn key in user-data was created by Proxmox. But hostname was correctly set up.

user-data of ubuntu

#cloud-config
hostname: ubuntu
manage_etc_hosts: true
chpasswd:
  expire: False
users:
  - default
package_upgrade: true

Environment details

• Cloud-init version: /usr/bin/cloud-init 23.1.1-10.el8.alma.1
• Operating System Distribution: NAME="AlmaLinux" VERSION="8.9 (Midnight Oncilla)"
• Cloud provider, platform or installer type: Proxmox 7.3-4

cloud-init logs

cloud-init.zip

Links

Similar topic on Proxmox forum

[aciba90]

Thanks, @kovalroma, for making cloud-init better.

The difference between Ubuntu and Almalinux is that Almalinux sets prefer_fqdn to True, this value determines whether fqdn is preferred over hostname when prefer_fqdn_over_hostname is not given in the user-data.

cc_set_hostname calls util.get_hostname_fqdn, and this function computes the fqdn using cloud metadata information (in your case QEMU), using cloud.get_hostname, but ignoring that fqdn is localhost (default fallback or explicitly set as that in the metadata).

Adding up the previous paragraphs results in cloud-init setting up the hostname as localhost.

As a workaround, you could set prefer_fqdn_over_hostname to false in the user-data. One possible way to solve this is to prefer hostname over fqdn if fqdn is the default localhost, returning that info from util.get_hostname_fqdn and extending HostnameFqdnInfo.

In order to verify what's the qemu metadata, could you please collect and attach the full cloud-init logs, making sure that any sensitive information is redacted?

Thanks.

[kovalroma]

Hello @aciba90, and thank you for your detailed explanation. Attached 2 logs. cloud-init_hostname_alma-tst.tar.gz -> Log generated on VMs named alma-tst cloud-init_hostname_alma-tst.lan.tar.gz -> Log generated on VMs named alma-tst.lan cloud-init_hostname_alma-tst.lan.tar.gz cloud-init_hostname_alma-tst.tar.gz