Modifying an instance network interface configuration

Here is how you can migrate an instance to a new network or add a secondary interface to an existing instance.

Find the instance name that you want to modify:

nova list

List all interfaces attached to an instance:

nova interface-list <server>

Detach an interface from your instance:

nova interface-detach <server> <port_id> 

Find the netowork ID of where you would like to attach your new interface:

nova net-list

Attach a new network interface to your network ID

nova interface-attach --net-id <net_id> <server>

Voila!