RouteS

cat etc network interfaces

source /etc/network/interfaces.d/*

auto lo
iface lo inet loopback

allow-hotplug ens4
iface ens4 inet dhcp

# "Failover"
auto ens3:0
allow-hotplug ens3:0
iface ens3:0 inet static
address 54.39.247.238
netmask 255.255.255.255
broadcast 54.39.247.238

ip a

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether fa:16:3e:d6:b1:f2 brd ff:ff:ff:ff:ff:ff
    inet 54.39.183.154/32 brd 54.39.183.154 scope global ens3
       valid_lft forever preferred_lft forever
    inet 54.39.247.238/32 brd 54.39.247.238 scope global ens3:0
       valid_lft forever preferred_lft forever
    inet6 fe80::f816:3eff:fed6:b1f2/64 scope link
       valid_lft forever preferred_lft forever
3: br-c078fd29c59d: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default
    link/ether 02:42:14:43:15:ef brd ff:ff:ff:ff:ff:ff
    inet 172.31.0.1/16 brd 172.31.255.255 scope global br-c078fd29c59d
       valid_lft forever preferred_lft forever
    inet6 fe80::42:14ff:fe43:15ef/64 scope link
       valid_lft forever preferred_lft forever
22: veth4a8125d@if21: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master br-70598df85260 state UP group default
    link/ether 66:13:e1:d6:2c:0b brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet6 fe80::6413:e1ff:fed6:2c0b/64 scope link
       valid_lft forever preferred_lft forever

...

ip route

default via 54.39.176.1 dev ens3
54.39.176.1 dev ens3 scope link
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown
172.19.0.0/16 dev br-bd39d7b126c2 proto kernel scope link src 172.19.0.1 linkdown

...

sbin route -n

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         54.39.176.1     0.0.0.0         UG    0      0        0 ens3
54.39.176.1     0.0.0.0         255.255.255.255 UH    0      0        0 ens3
172.17.0.0      0.0.0.0         255.255.0.0     U     0      0        0 docker0

...