After further investigation I would like to share one more important piece of information that explains the "reset" behaviour of the network configuration:

When a VM is started in 'Run once' mode, the initialization parameters supplied for that run are always passed by engine to cloud-init in the guest for application.

But if a VM is started in 'Run' mode, the initialization parameters are passed to cloud-init on the guest only if this is the first run (be it 'Run' or 'Run once'). On every consecutive run in 'Run' mode no parameters are passed to the guest, and therefore (as I quoted from the cloud-init documentation earlier in this thread) cloud-init falls back to DHCP configuration on the guest.

This is not an overlooked occurrence on engine's behalf but rather the designated behaviour.
When this behaviour was introduced into engine the reasoning was that after the initial configuration of the VM, there is no reason to resend the configuration on every 'Run' but only on 'Run once'. That's because 'Run once' may be used for out-of the ordinary instantiations of the VM.

Due to the behaviour of the current cloud-init package, this causes an unexpected side effect that should be dealt with by disabling cloud-init in one of the methods I described earlier in this thread.

HTH

On Wed, Nov 28, 2018 at 10:12 AM Eitan Raviv <eraviv@redhat.com> wrote:

On Wed, Nov 28, 2018 at 7:29 AM Mike Lykov <combr@ya.ru> wrote:
>
> 27.11.2018 16:15, Eitan Raviv пишет:
> > According to cloud-init 0.7.9 documentation cloud-init is configured
> > to run by default on each boot [1] and to render the user-selected
> > network configuration on first boot [2]. Also, in absence of a data
> > source to configure the network, it will fall back to configuring DHCP
> > on eth0 [2].
> >
> > As you noted, if you run a VM once, and then in the next regular run
> > the cloud-init flag is not selected in the VM configuration in engine,
> > there is no data-source and cloud-init falls back to dhcp as
> > documented.
>
> Thanks for the explanation. What intended use of this subsystem/feature
> are supposed to?
>
> My setup is not in cloud, it's local and use static IP adresses for VM.
> I do not want to configure each VM network in console by hand.
> I create VM from template (template have installed cloud-init package),
> configure cloud-init hostname/eth0 network in engine, and as "custom
> script" (at the same moment) I set a "touch
> /etc/cloud/cloud-init.disabled" ?

Either that or add custom script to disable just cloud-init network
re-config as you did manually.
Please consult the documentation for the custom script syntax and format
(e.g. search for 'runcmd' in
https://cloudinit.readthedocs.io/en/0.7.9/topics/examples.html)

> Then I "Run once" a VM, stop it, and run as usual without data source
> and fallback.
> Or I name network interface not "eth0" and therefore without need for
> custom script?

I did not test the outcome of assigning the static IP to another NIC.
Just sharing a thought...

>
>
> > The 'marker' file you refer to are also documented as follows:
> >
> > * disabling cloud-init altogether [1] with: touch /etc/cloud/cloud-init.disabled
> > * preventing cloud-init from configuring the network [2] with: echo
> > ‘network: {config: disabled}‘ >> /etc/cloud/cloud.cfg
> > whichever scenario is used to run a VM, this can be accomplished by
> > adding the above commands to the custom_script that cloud-init runs at
> > the last stage of its operation [3].
> >
> > There is possibly a third 'hack' that would not require any marker file:
> > * assign your static IP to a NIC not named 'eth0'
> > I have not tested it myself but it looks like a corollary of [2]
> >
> > HTH
> >
> > [1] https://cloudinit.readthedocs.io/en/0.7.9/topics/boot.html#generator
> > [2] https://cloudinit.readthedocs.io/en/0.7.9/topics/boot.html#local
> > [3] https://cloudinit.readthedocs.io/en/0.7.9/topics/boot.html#final
> >
> > On Wed, Nov 21, 2018 at 10:51 AM Mike Lykov <combr@ya.ru> wrote:
> >>
> >> 20.11.2018 15:30, Mike Lykov пишет:
> >>
> >>> "cloud-init used to use a "marker" file that it created on initial
> >>> execution. If that "marker" file existed it would not rerun on reboot. "
> >>> - are it not working in ovirt/this cloud-init version ?
> >>
> >> new restart:
> >>
> >> ----------
> >> 2018-11-21 12:40:53,314 - main.py[DEBUG]: Checking to see if files that
> >> we need already exist from a previous run that would allow us to stop early.
> >> 2018-11-21 12:40:53,315 - main.py[DEBUG]: Execution continuing, no
> >> previous run detected that would allow us to stop early.
> >> -------------
> >>
> >> which files it try to find ?
> >>
> >> --
> >> Mike
> >>
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