Digital Ocean floating IP gateway script (force droplet to use the assigned floating IP for outbound traffic as well as inbound traffic)

floating-ip-gateway.sh

#!/bin/bash
# Force outbound traffic through the attached floating IP
# Script must be run as root

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)

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

PHYS_GATEWAY=$(curl -s --connect-timeout $CURL_TIMEOUT http://169.254.169.254/metadata/v1/interfaces/public/0/ipv4/gateway)

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

# Check we haven't already got the floating IP as a default gateway
if [ ! -z $(ip route ls 0/0|awk '{print $3}'|grep "$GATEWAY_IP") ]; then
	echo "Error: gateway IP already a default route."
	exit 1
fi

# Add the new route with metric 100 before we remove any
ip route add default via $GATEWAY_IP dev $NET_INT metric 100

# Delete any other default gatways for this interface
ip route ls 0/0 dev $NET_INT|awk '{print $3}'|grep -v "$GATEWAY_IP"|xargs -n1 -I{}  ip route del default

# Add the physical gateway route with metric 101
ip route add default via $PHYS_GATEWAY dev $NET_INT metric 101

# Add route to DO metadata server via physical interface
ip route add 169.254.169.0/24 via $PHYS_GATEWAY dev $NET_INT

echo "Done."