Automatic Cloud Reboot On Updates
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
Cloud users can provide cloud-init metadata when creating a Fedora cloud instance and that metadata can contain instructions to update all packages on the system and reboot the system if any of those updated packages need a reboot to go into effect. Fedora cloud instances should write the /var/run/reboot-required file if a reboot is needed after a dnf update so that cloud-init can reboot the instance.
This issue originally surfaced in RHBZ 1275409.
Owner
- Name: Major Hayden
- Email: major@redhat.com
Current status
- Targeted release: Fedora Linux 39
- Last updated: 2023-05-18
- [<will be assigned by the Wrangler> devel thread]
- FESCo issue: <will be assigned by the Wrangler>
- Tracker bug: <will be assigned by the Wrangler>
- Release notes tracker: <will be assigned by the Wrangler>
Detailed Description
Fedora cloud instances use cloud-init to do the initial configuration of the instance. This includes setting up networking, assigning a hostname, adding users/groups, and arbitrary scripts. There are also two options that you can pass to cloud-init that are important for this change:
package_update: If set totrue, all installed packages are immediately updated on first bootpackage_reboot_if_required: If set totrue, and thepackage_updatestep wrote to/var/run/reboot-required, reboot the system immediately after updating packages
📚 For more details, see cloud-init's module reference for package_update.
Where does this /var/run/reboot-required file come from? On Debian and Ubuntu systems, apt automatically writes to /var/run/reboot-required if a reboot is needed after a package update. From there, cloud-init looks for the file (relevant cloud-init code) and if present, reboots the system immediately.
How do we write this file on Fedora? Fedora systems have a package called tracer and a corresponding dnf plugin, python3-dnf-plugin-tracer, that analyzes dnf updates and provides recommendations on reboots or user logouts to bring updates into effect on the system. A recent pull request added support for writing the /var/run/reboot-required file when a system reboot is recommended. The cloud-init tool can read this file after a package update and reboot if needed.
What does tracer's output look like?
[root@tracer-testing ~]# tracer
You should restart:
* Some applications using:
sudo systemctl restart NetworkManager
sudo systemctl restart auditd
sudo systemctl restart chronyd
sudo systemctl restart dbus-broker
sudo systemctl restart qemu-guest-agent
sudo systemctl restart sshd
sudo systemctl restart systemd-journald
sudo systemctl restart systemd-logind
sudo systemctl restart systemd-oomd
sudo systemctl restart systemd-resolved
sudo systemctl restart systemd-udevd
sudo systemctl restart systemd-userdbd
* These applications manually:
(sd-pam)
Additionally, there are:
- 3 processes requiring restart of your session (i.e. Logging out & Logging in again)
- 1 processes requiring reboot
[root@tracer-testing ~]# cat /var/run/reboot-required
Tracer says reboot is required
What do we need to do? Add the python3-dnf-plugin-tracer plugin to Fedora cloud images. No additional configuration is necessary. This action pulls in five packages that are about 2.1MB after installation:
======================================================================================= Package Arch Version Repository Size ======================================================================================= Installing: python3-dnf-plugin-tracer noarch 4.1.0-1.fc38 fedora 14 k Installing dependencies: python3-dnf-plugins-extras-common noarch 4.1.0-1.fc38 fedora 69 k python3-psutil x86_64 5.9.2-2.fc38 fedora 271 k python3-tracer noarch 0.7.8-5.fc38 fedora 172 k tracer-common noarch 0.7.8-5.fc38 fedora 22 k Transaction Summary ======================================================================================= Install 5 Packages Total download size: 547 k Installed size: 2.1 M
Feedback
One of the other ideas was to patch cloud-init to run tracer directly and avoid the /var/run/reboot-required file altogether. That would require a lot of work upstream in cloud-init to enable the functionality and we would still need the same set of packages installed in Fedora anyway.
Benefit to Fedora
This change allows Fedora cloud instances to behave in the same way that Debian-based instances already behave. When users request package updates with a reboot now, cloud-init performs the update but never reboots the system. This is an unexpected and confusing result for users who come to Fedora from other distributions.
Rebooting automatically could also reduce the attack surface of an instance that just came online since it would immediately reboot to put all package updates into effect on the system. This reduces the time that an unpatched instance is online prior to being fully patched.
Scope
- Proposal owners: This change is fairly isolated and only affects Fedora cloud users who request package updates followed by a reboot in their
cloud-initmetadata.
- Other developers: N/A
- Release engineering: N/A
- Policies and guidelines: N/A
- Trademark approval: N/A
- Alignment with Community Initiatives: N/A
Upgrade/compatibility impact
How To Test
User Experience
Dependencies
Contingency Plan
- Contingency mechanism: (What to do? Who will do it?) N/A (not a System Wide Change)
- Contingency deadline: N/A (not a System Wide Change)
- Blocks release? N/A (not a System Wide Change), Yes/No
Documentation
N/A (not a System Wide Change)