[Libguestfs] [PATCH FOR DISCUSSION ONLY 0/2] v2v: Copy static IP address information over for Windows guests (RHBZ#1626503).

[Richard W.M. Jones]

On Wed, Dec 05, 2018 at 01:18:49PM +0100, Fabien Dupont wrote:
> On Wed, Dec 5, 2018 at 12:01 PM Richard W.M. Jones <rjones at redhat.com>
> wrote:
> 
> > On Wed, Dec 05, 2018 at 09:01:16AM +0000, Roman Kagan wrote:
> > > On Tue, Dec 04, 2018 at 05:29:31PM +0000, Richard W.M. Jones wrote:
> > > > This patch is just for discussion.  There are still a couple of issues
> > > > that I'm trying to fix.
> > >
> > > Sorry if I missed the original discussion on that, but why is copying
> > > the static IP configuraition even considered to be a good thing?
> > >
> > > For one, it's unlikely that the IP address will remain valid in the
> > > target environment.
> >
> > For our v2v conversions (generally from VMware to oVirt or OpenStack)
> > we're trying to maintain a near-identical network configuration on
> > both sides.  So for example a guest will have the same MAC addresses
> > before and after and, if using DHCP, will pick up the exact same IP
> > address (probably served by the same DHCP server) and be able to
> > access the same set of services etc.
> >
> > Also we're doing like 1000s of VMs in one go, so manual
> > reconfiguration of anything is a non-starter.
> >
> > However let me describe the problem we're seeing, as it is a bit more
> > general and might even apply in some cloud scenarios.  If you have a
> > Windows guest which starts out with a static IP address (no DHCP) it
> > might be configured like this on VMware:
> >
> >   00:50:56:01:02:03   192.168.128.10   vmxnet3  "Ethernet0"  EnableDHCP=0
> >
> > After conversion we preserve the MAC address and add virtio drivers,
> > but the new netkvm.sys driver just adds a new network interface so
> > it'll end up like this:
> >
> >   (no hardware)       192.168.128.10   vmxnet3  "Ethernet0"  EnableDHCP=0
> >   00:50:56:01:02:03   (no address)     netkvm   "Ethernet1"  EnableDHCP=1
> >
> > It has no address in the second case because this is a non-DHCP
> > network.  (The DHCP situation is better because the second network
> > will be assigned the right IP address because of the preserved MAC
> > address, although it still has the unnecessary network adapter.)
> >
> > Note that Windows < 10 doesn't have a concept of persistent network
> > names like we do in Linux which mostly solves this problem.  (Windows
> > 10 on the other hand does save the MAC address in the Registry, but I
> > haven't fully investigated yet what it's doing.)
> >
> > Anyway if you have another suggestion how to solve this, I'm all ears ...
> > For other areas we'd fix things up using an Ansible post-copy script,
> > but in this case we can't do that since Ansible cannot reconfigure a
> > guest that has no working network.
> >
> 
> As you mention, using Ansible means that the IP address of the VM is
> correctly set.
> In another discussion, you mentioned using transient DHCP, but would mean
> that we reconfigure one of the NICs before conversion to use DHCP. That
> would alter the original VM.

No I don't think so.  The newly added netkvm NIC seems to come up with
EnableDHCP=1 (although NB I did not test in the end to end case
whether this means the Windows guest will get an address if a DHCP
server is available).

> And in the case of multiple NICs, how do we know which one to reconfigure.

The current patch has the same problem.  In the multiple NIC case for
Windows < 10 we don't know how the NICs were assigned to guest
hardware on the source and it seems hard to know without looking at
PCI address assignments which opens up a whole can of worms.

In Windows >= 10 it looks as if Windows is finally storing the
hardware MAC in the registry associated with each interface, so maybe
this problem will disappear in future.

> That would be quite specific to each customer, meaning customized
> playbook / role.

This is correct.

> And IIRC, there's a good chance that it breaks WinRM configuration with
> regards to certificates, meaning reconfiguring WinRM after DHCP and after
> conversion.

What is “WinRM configuration”?

> But maybe I'm too pessimistic ;)
> 
> 
> > > For two, in a typical cloud setup static IP addresses are configured by
> > > some sort of a cloud-specific management agent, and bypassing it is
> > > likely to cause conflicts.
> >
> 
> In the case of OpenStack, we keep the MAC address by creating the network
> ports with it and the IP address pre-allocated. This allows neutron to have
> working security groups.
> As Richard says, we're looking at the case of a massive migration where
> adapting the VM is out of scope. It's a mainly a 1:1 relationship. Anyway,
> we're still looking at more complex scenarios with tenant networks and
> floating IPs. It promises to be fun :)
> 
> 
> > > For three, network configuration is a notoriously complex thing.  I
> > > think I can recall a dozen of network configuration systems in Linux
> > > that claimed to provide the ultimate solution to all problems and none
> > > that delivered to the promise.  I guess in Windows the situation is
> > > hardly much simpler.  Creating yet another universal solution doesn't
> > > appear to be in scope for v2v (if realistic at all); and I'm not sure
> > > that having a very limited solution for a very basic use case only is
> > > better than explicitly telling the user not to rely on v2v for network
> > > configuration.
> >
> > Rich.

Rich.

-- 
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