Digital Ocean show how to use two IP addresses

twoip.sh

#!/bin/bash

NET_INT="eth0"
CURL_TIMEOUT=3

echo -n "Setting floating IP as the default gateway: "

# Check there's a floating IP attached to this droplet
if [ "$(curl -s --connect-timeout $CURL_TIMEOUT http://169.254.169.254/metadata/v1/floating_ip/ipv4/active)" != "true" ]; then
        echo "Error: this droplet doesn't have a floating IP assigned to it."
        exit 1
fi

# Get the gateway IP for the floating IP
GATEWAY_IP=$(curl -s --connect-timeout $CURL_TIMEOUT http://169.254.169.254/metadata/v1/interfaces/public/0/anchor_ipv4/gateway)
PUB_IP=$(curl -s --connect-timeout $CURL_TIMEOUT http://169.254.169.254/metadata/v1/interfaces/public/0/ipv4/address)

if [ -z "$GATEWAY_IP" ]; then
        echo "Error: failed getting gateway IP for this droplet."
        exit 1
fi

ip route replace default via $GATEWAY_IP dev $NET_INT

echo my default IP
curl -4 https://icanhazip.com/

echo my IP when done via pub IP
curl --interface $PUB_IP -4 https://icanhazip.com/