[libvirt] "migration_address must not be the address of the local machine: 127.0.0.1"

[Daniel P. Berrange]

On Wed, Nov 25, 2015 at 11:52:21AM +0100, Laszlo Ersek wrote:
> I recently upgraded my laptop from RHEL-7.1 to RHEL-7.2.
> 
> I always pay attention to *.rpmnew config files, and I manually diff and
> merge them with the ones I have in place.
> 
> I did the same with "/etc/libvirt/qemu.conf" this time.
> 
> Now libvirtd doesn't start for me. Systemd doesn't actually notice the
> startup failure (insert bitter joke about systemd being so much better
> than startup scripts); it only reports the service inactive/dead (=
> unstarted), rather than failed.
> 
> But, the libvirtd log file gives the reason:
> 
>     migration_address must not be the address of the local machine:
>     127.0.0.1
> 
> The error is easy to fix up in the config file, but my question is:
> 
> Why must migration_address not be the address of the local machine?

The migration address for incoming migration over TCP needs to be
a public facing IP address, otherwise the remote machine won't be
able to connect to it. If you configure migration_address on the
target machine to be 127.0.0.1, then obviously no migration client
connection will ever succeed, hence we consider 127.0.0.1 as an
invalid configuration.

> BTW, my purpose is not in-host migration (perhaps that's indeed
> unsupported, I don't know); I just want to lock down the incoming
> migration port (and not just with firewall rules).

What's wrong with using firewall rules ? IMHO you are describing
exactly the scenario that are intended to deal with.

> If there's a way to disable incoming migration in libvirtd, I'd be
> interested in that.

You could setup libvirt's API access control rules to deny the
"migrate" privilege to all users.  Using firewall rules is a
more secure solution though IMHO

Regards,
Daniel
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