auto eth0:0
iface eth0:0 inet static
  address W.X.Y.Z
  netmask 255.255.255.224

Trying W.X.Y.Z ...
* connect to W.X.Y.Z port 443 failed: Connection refused
* Failed to connect to domain.com port 443: Connection refused
* Closing connection 0
curl: (7) Failed to connect to domain.com port 443: Connection refused

The failover IP is W.X.Y.Z and is also the A record of domain.com

The /etc/hosts file for both nodes serverA and serverB looks like:

    127.0.0.1       localhost
    127.0.1.1       luminarhost
    xxx    serverA
    xxx    serverB

The /etc/network/interfaces of serverA

    ### Hetzner Online AG - installimage
    # Loopback device:
    auto lo
    iface lo inet loopback

    # device: eth0
    auto  eth0
    iface eth0 inet static
      address   xxx
      broadcast xxx
      netmask   xxx
      gateway   xxx
      # default route to access subnet
      up route add -net xxx netmask 255.255.255.224 gw xxx eth0

    iface eth0 inet6 static
      address xxx
      netmask xxx
      gateway xxx

    # failover ip
    auto eth0:0
    iface eth0:0 inet static
      address W.X.Y.Z
      netmask 255.255.255.224

and of serverB it is:

    ### Hetzner Online AG - installimage
    # Loopback device:
    auto lo
    iface lo inet loopback

    # device: eth0
    auto  eth0
    iface eth0 inet static
      address   xxx
      broadcast xxx
      netmask   xxx
      gateway   xxx
      # default route to access subnet
      up route add -net xxx netmask 255.255.255.192 gw xxx eth0

    iface eth0 inet6 static
      address xxx
      netmask xxx
      gateway xxx

    # failover ip
    auto eth0:0
    iface eth0:0 inet static
      address W.X.Y.Z
      netmask 255.255.255.224

#!/bin/sh

date >> /var/tmp/failover_after.txt
# this below line makes sure it deletes the floating ip after it successfully switched
set -o xtrace && ssh -o StrictHostKeyChecking=no $2 'ip addr del '"$1"'/32 dev `route | grep "^default" | grep -o "[^ ]*$"`' && set +o xtrace >> /var/tmp/failover_after.text

echo "To: yourmail@gmail.com
From: noreply@dummydomain.in
Subject: Heartbeat notice from `/bin/hostname`
Switched failover ip $1 from $2 to $3" | /usr/sbin/sendmail -t

# use https://github.com/course-hero/slacktee
echo "👍 Switch success for failover ip $1 from $2 to $3"| slacktee.sh

#!/bin/sh

date >> /var/tmp/failover_after.txt
set -o xtrace && ssh -o StrictHostKeyChecking=no $2 'ip addr del '"$1"'/32 dev `route | grep "^default" | grep -o "[^ ]*$"`' && set +o xtrace >> /var/tmp/failover_after.text

echo "To: yourmail@gmail.com
From: noreply@dummydomain.in
Subject: Heartbeat notice from `/bin/hostname`
Switched failover ip $1 from $2 to $3" >> /var/tmp/failover_after.txt

echo "To: nizam.sp@gmail.com
From: noreply@whereismytrain.in
Subject: Heartbeat notice from `/bin/hostname`
Switched failover ip $1 from $2 to $3" | /usr/sbin/sendmail -t

echo "👍 Switch success for failover ip $1 from $2 to $3"| slacktee.sh