Configure Failover IP in Ubuntu 18.04 OVH VPS

Default /etc/network/interfaces in Ubuntu 18.04 in OVH VPS look like following. Click here for Ubuntu 20.04 instructions.

root@vps624512:~# cat /etc/network/interfaces 
# ifupdown has been replaced by netplan(5) on this system.  See
# /etc/netplan for current configuration.
# To re-enable ifupdown on this system, you can run:
#    sudo apt install ifupdown
root@vps624512:~# 

First install

sudo apt install ifupdown -y

Configure Main IP

use “ip a” command to find out interface name and IP of the VPS

root@vps624512:~# ip a
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    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:  mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether fa:16:3e:f4:1e:fd brd ff:ff:ff:ff:ff:ff
    inet 51.77.149.182/32 scope global dynamic ens3
       valid_lft 49349sec preferred_lft 49349sec
    inet6 fe80::f816:3eff:fef4:1efd/64 scope link 
       valid_lft forever preferred_lft forever
root@vps624512:~#

In this case,

IP = 51.77.149.182
Interface Name = ens3

Use “route -n” command to find out gateway.

root@vps624512:~# route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         51.77.148.1     0.0.0.0         UG    100    0        0 ens3
51.77.148.1     0.0.0.0         255.255.255.255 UH    100    0        0 ens3
root@vps624512:~# 

GATEWAY = 51.77.148.1

Edit /etc/network/interfaces

vi /etc/network/interfaces

Add following

auto INTERFACE_NAME
iface INTERFACE_NAME inet static
    address SEVER_MAIN_IP
    netmask 255.255.255.255
    broadcast SEVER_MAIN_IP
    dns-nameservers 8.8.8.8 1.1.1.1
    post-up route add GATEWAY_IP dev INTERFACE_NAME
    post-up route add default gw GATEWAY_IP
    post-down route del default gw GATEWAY_IP
    post-down route del GATEWAY_IP dev INTERFACE_NAME

In the above, replace INTERFACE_NAME, SEVER_MAIN_IP and GATEWAY_IP.

For this server, i added.

auto ens3
iface ens3 inet static
    address 51.77.149.182
    netmask 255.255.255.255
    broadcast 51.77.149.182
    post-up route add 51.77.148.1 dev ens3
    post-up route add default gw 51.77.148.1
    post-down route del default gw 51.77.148.1
    post-down route del 51.77.148.1 dev ens3

Now reboot the server.

Once server is back online, you can configure failover IPS.

Configure Failover IP

Use following script to generate your config, add in end of /etc/network/inferfaces file

php script to generate ip config

Once configured, you need to reboot the servr.

Verify IP is up with fping command.

fping
/etc/inetnet/interfaces