Hi. I have two LXD hypervisors in a cluster, running a few containers on a ZFS storage. Hypervisors run both on Debian 10, and I would like to upgrade them both to Debian 11. Both lxc and lxd are installed with snap, and are in version 4.18. Both systems have 300+ days of uptime, as do the lxc services (so if the packages are in v4.18, I am not sure in which version are the running services).
My question is a bit general: what upgrade policy would you do to safely upgrade both hypervisors to Debian 11? Must I upgrade both the hypervisors at the same time, or can I move all the containers on one hypervisor, upgrade the other, then move all the containers to the updated hypervisor, and then upgrade the other?
I was thinking of:
- Do applicative backups of the containers. Store them somewhere safe.
- Do snapshots of the containers.
- Restart all the containers, to be sure they can.
- Restart the lxd services on both hypervisors, to be sure they can.
- Evacuate hypervisor A from the cluster. Then reboot it, to be sure it can.
- Plug back hypervisor A in the cluster, then evacuate hypervisor B, and then reboot it, to be sure it can.
- Plug back hypervisor B. Take a coffee.
- Evacuate hypervisor A. Upgrade Debian. Reboot.
- Plug back hypervisor A. Evacuate hypervisor B. Upgrade Debian. Reboot.
- Plug back hypervisor B.
- Does it seem reasonable to you?
- What can go wrong in this process?
- What would you do to prevent things to go wrong?
- What documentation piece should I read that I missed?
Thank you for your help.