[pve-devel] cloudinit: question about cloudinit pending values && hostname/mac address changes

[Thomas Lamprecht]

On 21.02.21 18:47, aderumier at odiso.com wrote:
> I have some question about cloudinit hotplug pending values.
> 
> Currently, when vm is running, we keep cloudinit specific values
> (ipconfigX, dns, ssh,...)  in pending until we regenerate image
> manually. 
> 
> But some other change, like vm name (use for hostname), or nic mac
> address . (use to match interface in config nodrive format), are not
> keeped as pending.
> 
> Why don't we simply auto regenerate the cloudinit config drive after
> changes? (and don't use pending values like "pending  cdrom
> generation").

IMO OK, wasn't the other stuff done because of some changes cannot be
applied live?

> 
> Anyway, when vm is offline, we don't have pending state at all, and
> config drive is generated only after at vmstart.
> 
> Also, currently, to regenerated the iso, we need 2 api call,  
> 1 to remove cdrom ,  1 to replug cdrom with new config.
> 
> I really would like to be able to change cloud-init config like lxc, 
> simply update values, and get them auto apply.
> 
> What do you think about it ?

Sounds OK to me, without much thinking into regression possibilities.

In general, I'd like to simplify cloud init anyway, IMO the whole
special disk handling just brought us bug after bug with clone, migrate,
...

I'd like to generate the image just in memory (e.g., /run/qemu-server ?)
and just attach it from there (e.g., just using the first free IDE bus
slot, adding new IDE CD ROM devices need reboot anyway, so if it has to
move to another free slot its not a problem).

For backups we already save the config with the state applied, so there
no change is required.

For live migration we'd need to transfer the current state, not much extra
work but needs a few changes.

For live-snapshots we'd need to save the state too (so that processes
which currently have that open do not die if it changed), also a bit of
changes required.

But I think that would simplify this whole thing a lot, and also would
not require the user to add a cloudinit cdrom to the VM, just configure
it and be done.