Google Cloud Dynamic DNS - Update if current IP mismatches DNS entry.

dynamic-dns.sh

#!/bin/bash
# Google Cloud Dynamic DNS
# Run this under some kind of cron/timer job.

IP="$(dig +short myip.opendns.com @resolver1.opendns.com)"
ZONE_NAME="com-yourdomain"
DNS_NAME="dynamic-dns-entry.yourdomain.com"

gcloud dns record-sets list -z=$ZONE_NAME --name=$DNS_NAME --type=A --format='value(name,type,ttl,rrdatas)' | while read name type ttl data ; do
	LAST_IP=$data
	echo Last IP was \"$LAST_IP\", current IP is \"$IP\".
	if [ "$LAST_IP" != "$IP" ]
	then
		echo Updating $DNS_NAME dynamic dns entry to \"$IP\".
		gcloud dns record-sets transaction start -z=$ZONE_NAME
		gcloud dns record-sets list -z=$ZONE_NAME --name=$DNS_NAME --type=A --format='value(name,type,ttl,rrdatas)' | while read name type ttl data ; do
			gcloud dns record-sets transaction remove -z=$ZONE_NAME --name=$name --type=$type --ttl=$ttl "$data";
		done
		gcloud dns record-sets transaction add -z=$ZONE_NAME --name=$DNS_NAME --ttl=300 --type=A $IP
		gcloud dns record-sets transaction execute -z=$ZONE_NAME
		rm -f transaction.yaml
	else
		echo No update of the dynamic dns entry is necessary.
	fi
done