Add upgrade documentation for XOSTOR

[Wescoeur]

Before submitting the pull request, you must agree with the following statements by checking both boxes with a 'x'.

• "I accept that my contribution is placed under the CC BY-SA 2.0 license [1]."
• "My contribution complies with the Developer Certificate of Origin [2]."

[1] https://creativecommons.org/licenses/by-sa/2.0/
[2] https://docs.xcp-ng.org/project/contributing/#developer-certificate-of-origin-dco

[stormi]

What if the linstor and satellite versions are not the same in 8.2 and 8.3 when they proceed with the upgrade? Will it work?

The document doesn't talk about live migrating the VMs. Is it because it "just works" so there's no need to focus on it?

[stormi]

Is it wise to wait a little after the toolstack restart, or maybe to grep the logs for the line which indicates that startup has completed?

[Wescoeur]

I would say that waiting for the previous command to return is enough to use the plugins API.

[stormi]

Why can it be not connected?

[Wescoeur]

You can't plug the PBD without the LINSTOR packages (before this point it was not the case), so I guess most of the time you have to manually connect the PBD unless the XAPI tries again on its own, which to my knowledge is not the case.

[Wescoeur]

What if the linstor and satellite versions are not the same in 8.2 and 8.3 when they proceed with the upgrade? Will it work?

If the LINSTOR packages are newer on the new XCP-ng version, it won't work. I honestly have no idea how to handle this case without waiting several months before updating the LINSTOR packages in our repos to not break the migration.

The document doesn't talk about live migrating the VMs. Is it because it "just works" so there's no need to focus on it?

No issue on this side. We can handle that like a classic upgrade.

[Nambrok]

To handle upgrade with different versions on 8.2 to 8.3:
Installer detect XOSTOR version and write on disk in /etc/firstboot.d/.
firstboot script use this file to identify the correct version of linstor-satellite/controller on 8.3 to install to maintain VERSION compatibility.
Installer need to write a warning about needing internet access to repo.vates.tech to fetch the linstor package of the correct version. If they are airgap, they need to follow documentation.
TODO: What do we do if install fail?