Comment 27 for bug 1899487

I guess the third option that could trigger network re-write across migration or MTU changes would be that OpenStack updates the instance-id at http://169.254.169.254/latest/meta-data/instance-id whenever the MTU value changes. By default, cloud-init re-provisions an OpenStack machine with any user-data, vendor-data and network_data.json anytime the instance-id changes.

 It's a pretty big hammer, and no additional configuration would be needed for default cloud-init behavior. Upon, if cloud-init detects a change in http://169.254.169.254/latest/meta-data/instance-id it would re-provision the system based current network_data.json and user_data provided from openstack at that time. I'd be wary of this full reprovision scenario as it will also involve cloud-init re-running ssh host key generation so SSH automation, and any user creation, password setting based on userdata which may introduce obstacles due to unrecognized SSH host keys when trying to connect to the migrated instance. Or resetting initial user passwords which could have changed over the life of the VM.