Implementation – WAN Redirection
If the IP of the VM changes, we use IP tunneling and Dynamic DNS to prevent dropped network connections.
Just before the source VM is paused, an IP tunnel is created from the source to destination using iproute2.
Once the destination VM is capable of responding to requests at its new IP, Dynamic DNS forwards the requests to the new IP.
Packets that arrive during the final stage of migration are simply dropped.
Once no connections exist that use the old IP, the tunnel is torn down.
Practically, this works because:
The source server only needs to cooperate for a short time, most network connections are short-lived and if nothing else, it’s no worse than what you get if the VM doesn’t even try.