OVH OpenStack server secondary interface is sometimes ens4

It is usually ens7 but can sometime be ens4. It is possible to force the name to ens7 by adding the following:

$ echo 'SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="fa:16:3e:37:9b:29", NAME="ens7"' >> /etc/udev/rules.d/70-persistent-net.rules

Where the mac is the address associated with ens4. After rebooting the interface will be named ens7.