Testing Fedora CoreOS updates

Make sure that you have completed the steps described in the initial setup page before starting this tutorial.

In this tutorial, we will not focus on provisioning but on what happens during updates and the options that are available in case of failures.

Downloading an older Fedora CoreOS release

One of the defining features of Fedora CoreOS is automatic updates. To see them in action, we have to download an older Fedora CoreOS release. Start by picking an older release from the Fedora CoreOS release page:

# replace "XX.XXXXXXXX.X.X" with one of older release IDs from the release page above (e.g. "34.20210919.3.0")
RELEASE="XX.XXXXXXXX.X.X"
curl -O https://builds.coreos.fedoraproject.org/prod/streams/stable/builds/$RELEASE/x86_64/fedora-coreos-$RELEASE-qemu.x86_64.qcow2.xz
curl -O https://builds.coreos.fedoraproject.org/prod/streams/stable/builds/$RELEASE/x86_64/fedora-coreos-$RELEASE-qemu.x86_64.qcow2.xz.sig

Once the archive has been downloaded, make sure to verify its integrity:

gpg --verify fedora-coreos-$RELEASE-qemu.x86_64.qcow2.xz.sig
Look for "Good signature from" in the output.

Once you have verified the archive, you can extract it with:

unxz fedora-coreos-$RELEASE-qemu.x86_64.qcow2.xz

To make the tutorial simpler, you should rename this image to a shorter name:

mv fedora-coreos-$RELEASE-qemu.x86_64.qcow2 fedora-coreos-older.qcow2

Writing the Butane config and converting to Ignition

We will create a Butane config that:

  • Sets up console autologin.

  • Raise kernel console logging level to hide audit messages from the console.

  • Add an SSH Key for the core user.

Let’s write this Butane config to a file called updates.bu:

variant: fcos
version: 1.4.0
passwd:
  users:
    - name: core
      ssh_authorized_keys:
        - ssh-rsa AAAA...
systemd:
  units:
    - name: serial-getty@ttyS0.service
      dropins:
      - name: autologin-core.conf
        contents: |
          [Service]
          # Override Execstart in main unit
          ExecStart=
          # Add new Execstart with `-` prefix to ignore failure
          ExecStart=-/usr/sbin/agetty --autologin core --noclear %I $TERM
          TTYVTDisallocate=no
storage:
  files:
    - path: /etc/profile.d/systemd-pager.sh
      mode: 0644
      contents:
        inline: |
          # Tell systemd to not use a pager when printing information
          export SYSTEMD_PAGER=cat
    - path: /etc/sysctl.d/20-silence-audit.conf
      mode: 0644
      contents:
        inline: |
          # Raise console message logging level from DEBUG (7) to WARNING (4)
          # to hide audit messages from the interactive console
          kernel.printk=4
Optionally you can replace the SSH pubkey in the yaml file with your own public key so you can log in to the booted instance. If you choose not to do this you’ll still be auto logged in to the serial console.

Run Butane to convert that to an Ignition config:

butane --pretty --strict updates.bu --output updates.ign

Startup and initial update

Now let’s provision it. Make sure that you are starting from the older Fedora CoreOS image in this step:

# Setup the correct SELinux label to allow access to the config
chcon --verbose --type svirt_home_t updates.ign

# Start a Fedora CoreOS virtual machine
virt-install --name=fcos --vcpus=2 --ram=2048 --os-variant=fedora-coreos-stable \
    --import --network=bridge=virbr0 --graphics=none \
    --qemu-commandline="-fw_cfg name=opt/com.coreos/config,file=${PWD}/updates.ign" \
    --disk=size=20,backing_store=${PWD}/fedora-coreos-older.qcow2

As the system is not up to date, Zincati will notice this and will start updating the system. You should see the update process happening right away:

All necessary network services may not be up and running during the initial check. In such case Zincati will check for updates again in about 5 minutes. 
[core@localhost ~]$ systemctl status --full zincati.service
● zincati.service - Zincati Update Agent
     Loaded: loaded (/usr/lib/systemd/system/zincati.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2021-11-30 13:56:05 UTC; 5min ago
       Docs: https://github.com/coreos/zincati
   Main PID: 1026 (zincati)
     Status: "found update on remote: 35.20211029.3.0"
      Tasks: 11 (limit: 2262)
     Memory: 20.0M
        CPU: 192ms
     CGroup: /system.slice/zincati.service
             ├─1026 /usr/libexec/zincati agent -v
             └─2308 rpm-ostree deploy --lock-finalization revision=ccdac241ed4b83b55e4d72e864923679c00a15804fbea7d1e638e67c2a08dd5c --disallow-downgrade

Nov 30 13:56:04 localhost zincati[1026]: [INFO  zincati::cincinnati] Cincinnati service: https://updates.coreos.fedoraproject.org
Nov 30 13:56:04 localhost zincati[1026]: [INFO  zincati::cli::agent] agent running on node '0d817dcff294404895a7a33727980fe8', in update group 'default'
Nov 30 13:56:04 localhost zincati[1026]: [INFO  zincati::update_agent::actor] registering as the update driver for rpm-ostree
Nov 30 13:56:05 localhost zincati[1026]: [INFO  zincati::update_agent::actor] initialization complete, auto-updates logic enabled
Nov 30 13:56:05 localhost zincati[1026]: [INFO  zincati::strategy] update strategy: immediate
Nov 30 13:56:05 localhost zincati[1026]: [INFO  zincati::update_agent::actor] reached steady state, periodically polling for updates
Nov 30 13:56:05 localhost systemd[1]: Started Zincati Update Agent.
Nov 30 13:56:05 localhost zincati[1026]: [ERROR zincati::cincinnati] failed to check Cincinnati for updates: client-side error: error sending request for url (https://updates.coreos.fedoraproject.org/v1/graph?os_checksum=6334e11901fba7403600522286d817b520eeb15b66b341b392e0c08ed2576b74&stream=stable&os_version=34.20210919.3.0&basearch=x86_64&group=default&node_uuid=0d817dcff294404895a7a33727980fe8&platform=qemu): error trying to connect: dns error: failed to lookup address information: Name or service not known
Nov 30 14:01:12 localhost zincati[1026]: [INFO  zincati::cincinnati] current release detected as not a dead-end
Nov 30 14:01:13 localhost zincati[1026]: [INFO  zincati::update_agent::actor] target release '35.20211029.3.0' selected, proceeding to stage it

[core@localhost ~]$ rpm-ostree status
State: busy
AutomaticUpdatesDriver: Zincati
  DriverState: active; found update on remote: 35.20211029.3.0
Transaction: deploy --lock-finalization revision=ccdac241ed4b83b55e4d72e864923679c00a15804fbea7d1e638e67c2a08dd5c --disallow-downgrade
  Initiator: caller :1.28
Deployments:
● fedora:fedora/x86_64/coreos/stable
                   Version: 34.20210919.3.0 (2021-10-04T17:11:11Z)
                    Commit: 6334e11901fba7403600522286d817b520eeb15b66b341b392e0c08ed2576b74
              GPGSignature: Valid signature by 8C5BA6990BDB26E19F2A1A801161AE6945719A39

[core@localhost ~]$ systemctl status --full zincati.service
● zincati.service - Zincati Update Agent
     Loaded: loaded (/usr/lib/systemd/system/zincati.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2021-11-30 13:56:05 UTC; 7min ago
       Docs: https://github.com/coreos/zincati
   Main PID: 1026 (zincati)
     Status: "update staged: 35.20211029.3.0; reboot delayed due to active user sessions"
      Tasks: 5 (limit: 2262)
     Memory: 16.6M
        CPU: 229ms
     CGroup: /system.slice/zincati.service
             └─1026 /usr/libexec/zincati agent -v

Nov 30 13:56:04 localhost zincati[1026]: [INFO  zincati::cli::agent] agent running on node '0d817dcff294404895a7a33727980fe8', in update group 'default'
Nov 30 13:56:04 localhost zincati[1026]: [INFO  zincati::update_agent::actor] registering as the update driver for rpm-ostree
Nov 30 13:56:05 localhost zincati[1026]: [INFO  zincati::update_agent::actor] initialization complete, auto-updates logic enabled
Nov 30 13:56:05 localhost zincati[1026]: [INFO  zincati::strategy] update strategy: immediate
Nov 30 13:56:05 localhost zincati[1026]: [INFO  zincati::update_agent::actor] reached steady state, periodically polling for updates
Nov 30 13:56:05 localhost systemd[1]: Started Zincati Update Agent.
Nov 30 13:56:05 localhost zincati[1026]: [ERROR zincati::cincinnati] failed to check Cincinnati for updates: client-side error: error sending request for url (https://updates.coreos.fedoraproject.org/v1/graph?os_checksum=6334e11901fba7403600522286d817b520eeb15b66b341b392e0c08ed2576b74&stream=stable&os_version=34.20210919.3.0&basearch=x86_64&group=default&node_uuid=0d817dcff294404895a7a33727980fe8&platform=qemu): error trying to connect: dns error: failed to lookup address information: Name or service not known
Nov 30 14:01:12 localhost zincati[1026]: [INFO  zincati::cincinnati] current release detected as not a dead-end
Nov 30 14:01:13 localhost zincati[1026]: [INFO  zincati::update_agent::actor] target release '35.20211029.3.0' selected, proceeding to stage it
Nov 30 14:02:55 localhost zincati[1026]: [INFO  zincati::update_agent::actor] update staged: 35.20211029.3.0

Shortly after the update has been staged, the system should reboot to apply the latest update. You may need to stop the autologin service to initiate the reboot.

Broadcast message from Zincati at Tue 2021-11-30 14:02:55 UTC:
New update 35.20211029.3.0 is available and has been deployed.
If permitted by the update strategy, Zincati will reboot into this update when all
interactive users have logged out, or in 10 minutes, whichever comes earlier.
Please log out of all active sessions in order to let the auto-update process continue.
[core@localhost ~]$ sudo systemctl stop serial-getty@ttyS0.service

When we log back in we can view the current version of Fedora CoreOS is now the latest one. The rpm-ostree status output will also show the older version, which still exists in case we need to rollback:

[core@localhost ~]$ rpm-ostree status
State: idle
AutomaticUpdatesDriver: Zincati
  DriverState: active; periodically polling for updates (last checked Tue 2021-11-30 14:22:41 UTC)
Deployments:
● fedora:fedora/x86_64/coreos/stable
                   Version: 35.20211029.3.0 (2021-11-17T23:45:08Z)
                    Commit: ccdac241ed4b83b55e4d72e864923679c00a15804fbea7d1e638e67c2a08dd5c
              GPGSignature: Valid signature by 787EA6AE1147EEE56C40B30CDB4639719867C58F

  fedora:fedora/x86_64/coreos/stable
                   Version: 34.20210919.3.0 (2021-10-04T17:11:11Z)
                    Commit: 6334e11901fba7403600522286d817b520eeb15b66b341b392e0c08ed2576b74
              GPGSignature: Valid signature by 8C5BA6990BDB26E19F2A1A801161AE6945719A39
The currently booted deployment is denoted by the ● character.

You can view the differences between the two versions by running an rpm-ostree db diff command:

[core@localhost ~]$ rpm-ostree db diff
ostree diff commit from: rollback deployment (6334e11901fba7403600522286d817b520eeb15b66b341b392e0c08ed2576b74)
ostree diff commit to:   booted deployment (ccdac241ed4b83b55e4d72e864923679c00a15804fbea7d1e638e67c2a08dd5c)
Upgraded:
  NetworkManager 1:1.30.6-1.fc34 -> 1:1.32.12-2.fc35
  NetworkManager-cloud-setup 1:1.30.6-1.fc34 -> 1:1.32.12-2.fc35
  NetworkManager-libnm 1:1.30.6-1.fc34 -> 1:1.32.12-2.fc35
  NetworkManager-team 1:1.30.6-1.fc34 -> 1:1.32.12-2.fc35
  NetworkManager-tui 1:1.30.6-1.fc34 -> 1:1.32.12-2.fc35
  WALinuxAgent-udev 2.3.1.1-1.fc34 -> 2.3.1.1-2.fc35
  ...

Reverting to the previous version

If the system is not functioning fully for whatever reason we can go back to the previous version:

[core@localhost ~]$ sudo rpm-ostree rollback --reboot

After logging back in after reboot we can see we are now booted back into the old deployment from before the upgrade occurred:

[core@localhost ~]$ rpm-ostree status
State: idle
AutomaticUpdatesDriver: Zincati
  DriverState: active; periodically polling for updates (last checked Tue 2021-11-30 15:17:47 UTC)
Deployments:
● fedora:fedora/x86_64/coreos/stable
                   Version: 34.20211031.3.0 (2021-11-08T23:55:31Z)
                    Commit: 056a1508fad0eecb740cf10a949d2292e11084195f1defbf455f418a5991daa2
              GPGSignature: Valid signature by 8C5BA6990BDB26E19F2A1A801161AE6945719A39

  fedora:fedora/x86_64/coreos/stable
                   Version: 35.20211029.3.0 (2021-11-17T23:45:08Z)
                    Commit: ccdac241ed4b83b55e4d72e864923679c00a15804fbea7d1e638e67c2a08dd5c
              GPGSignature: Valid signature by 787EA6AE1147EEE56C40B30CDB4639719867C58F

And you can also verify that Zincati will not try to update to the new version we just rollbacked from:

[core@localhost ~]$ systemctl status --full zincati.service
● zincati.service - Zincati Update Agent
     Loaded: loaded (/usr/lib/systemd/system/zincati.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2021-11-30 15:36:04 UTC; 19s ago
       Docs: https://github.com/coreos/zincati
   Main PID: 802 (zincati)
     Status: "found update on remote: 34.20211031.3.0"
      Tasks: 10 (limit: 2262)
     Memory: 23.4M
        CPU: 169ms
     CGroup: /system.slice/zincati.service
             ├─ 802 /usr/libexec/zincati agent -v
             └─2814 rpm-ostree deploy --lock-finalization revision=056a1508fad0eecb740cf10a949d2292e11084195f1defbf455f418a5991daa2 --disallow-downgrade

Nov 30 15:36:03 localhost zincati[802]: [INFO  zincati::cli::agent] agent running on node '8d67840e25884927aaeb72f64e100046', in update group 'default'
Nov 30 15:36:03 localhost zincati[802]: [INFO  zincati::update_agent::actor] registering as the update driver for rpm-ostree
Nov 30 15:36:04 localhost zincati[802]: [INFO  zincati::update_agent::actor] found 1 other finalized deployment
Nov 30 15:36:04 localhost zincati[802]: [INFO  zincati::update_agent::actor] deployment 35.20211029.3.0 (ccdac241ed4b83b55e4d72e864923679c00a15804fbea7d1e638e67c2a08dd5c) will be excluded from being a future update target
Nov 30 15:36:04 localhost zincati[802]: [INFO  zincati::update_agent::actor] initialization complete, auto-updates logic enabled

Cleanup

Now let’s take down the instance for the next test. Disconnect from the serial console by pressing CTRL + ] or from SSH and then destroy the machine:

virsh destroy fcos
virsh undefine --remove-all-storage fcos

Conclusion

In these tutorials we have learned a little bit about Fedora CoreOS. We have learned how it is delivered as a pre-created disk image, how it is provisioned in an automated fashion via Ignition, and also how automated updates are configured and achieved via Zincati and rpm-ostree. The next step is to try out Fedora CoreOS for your own use cases and join the community!