OVH VPS Configure failover IP in Ubuntu

On Ubuntu

Default config look like

root@zecurecode:~# cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# Source interfaces
# Please check /etc/network/interfaces.d before changing this file
# as interfaces may have been defined in /etc/network/interfaces.d
# See LP: #1262951
source /etc/network/interfaces.d/*.cfg

root@zecurecode:~#

/etc/network/interfaces.d/50-cloud-init.cfg is used to auto configure network interface with dhcp.

root@zecurecode:~# cat /etc/network/interfaces.d/50-cloud-init.cfg 
# This file is generated from information provided by
# the datasource.  Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
auto lo
iface lo inet loopback

auto ens3
iface ens3 inet dhcp
root@zecurecode:~# 

First find the gateway used by the VPS.

root@zecurecode:~# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         51.254.32.1     0.0.0.0         UG    0      0        0 ens3
51.254.32.1     0.0.0.0         255.255.255.255 UH    0      0        0 ens3
root@zecurecode:~# 

We found the gateway IP 51.254.32.1

The VPS had main IP of the server is 51.254.35.58 and secondary IPS 94.23.153.137, 178.32.52.159, 178.32.49.157

Here is the modified /etc/network/interfaces

root@zecurecode:~# cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# Source interfaces
# Please check /etc/network/interfaces.d before changing this file
# as interfaces may have been defined in /etc/network/interfaces.d
# See LP: #1262951
#source /etc/network/interfaces.d/*.cfg

auto ens3
iface ens3 inet static
    address 51.254.35.58
    netmask 255.255.255.255
    broadcast 51.254.35.58
    post-up route add 51.254.32.1 dev ens3
    post-up route add default gw 51.254.32.1
    post-down route del default gw 51.254.32.1
    post-down route del 51.254.32.1 dev ens3

auto ens3:1
iface ens3:1 inet static
    address 94.23.153.137
    netmask 255.255.255.255
    broadcast 94.23.153.137

auto ens3:2
iface ens3:2 inet static
    address 178.32.52.159
    netmask 255.255.255.255
    broadcast 178.32.52.159

auto ens3:3
iface ens3:3 inet static
    address 178.32.49.157
    netmask 255.255.255.255
    broadcast 178.32.49.157


root@zecurecode:~# 

Here is a PHP script to create OVH failover IP config for Ubuntu/Debian.

https://gist.github.com/serverok/991f7ccd1be36cbc579e8d55caf39715