DNS check - Check DNS entry matches your public ip

dns_check.sh

#!/bin/sh
set -e

export DNS_NAME=$1

IP="NOTSET"
DNS_IP=$(nslookup $DNS_NAME 8.8.8.8 | awk -F': ' 'NR==5 { print $2 } ')
echo "Checking DNS - IP: $IP DNS_IP: $DNS_IP DNS_NAME: $DNS_NAME"
ATTEMPTS=25
I=0
while [ "$IP" != "$DNS_IP" ] && [ $I -lt $ATTEMPTS ]
do
    DNS_IP=$(nslookup $DNS_NAME 8.8.8.8 | awk -F': ' 'NR==5 { print $2 } ')
    IP=$(curl -s whatismyip.akamai.com)
    echo "DNS_IP: $DNS_IP"
    echo "EXTERNAL_IP: $IP"
    sleep 10

    I=$(( $I + 1 ))
done

if [ "$IP" != "$DNS_IP" ]
then 
    echo "DNS not pointing to our location: FAILED!"
    sleep 10
    exit 1
fi