Cloud DNS record set configuration during instance startup.

clouddns-update

#!/bin/bash

#
# Helper script to auto-configure a Cloud DNS record during
# compute engine instance startup.
#
# Setup:
# 1. Download and install the script in the instance:
#      curl -L https://gist.github.com/ronoaldo/6d6f97bc20a5a40c4aac5e4fa6c09dd5/raw/ > /etc/init.d/clouddns-update
# 2. Give this script permissions and setup as startup daemon
#      chmod +x /etc/init.d/clouddns-update
#      update-rc.d -f clouddns-update defaults
# 3. Add instance metadata:
#      clouddns-zone: the hosted zone name (e.g. my-hosted-zone)
#      clouddns-name: the record name (e.g. sub.domain.com)
#      clouddns-project: (optional) if the VM project does not contains the hosted zone
# 4. Profit!
#

### BEGIN INIT INFO
# Provides:          boxdns
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Updates the DNS dynamically
# Description:       Updates the DNS of the box dynamically
### END INIT INFO

metadata() {
	curl --fail -s -H Metadata-Flavor:Google "http://metadata/computeMetadata/v1/$1"
}

# Use Cloud DNS to update hostname
export DNS_ZONE="$(metadata 'instance/attributes/clouddns-zone')"
export DNS_NAME="$(metadata 'instance/attributes/clouddns-name')"
export DNS_PROJECT="$(metadata 'instance/attributes/clouddns-project')"
export PUBLIC_IP=$(metadata 'instance/network-interfaces/0/access-configs/0/external-ip')

replace_dns() {
	TYPE="$1"
	DATA="$2"
	dns="gcloud dns --project=$DNS_PROJECT record-sets"
	echo "Configuring cloud DNS with 60s TTL"
	$dns transaction start -z $DNS_ZONE
	$dns list -z $DNS_ZONE --name $DNS_NAME --format='value(name,type,ttl,rrdatas)' | while read name type ttl data ; do
		$dns transaction remove -z $DNS_ZONE --name=$name --type=$type --ttl=$ttl "$data";
	done
	$dns transaction add -z $DNS_ZONE --name="$DNS_NAME" --ttl=60 --type "$TYPE" "$DATA"
	$dns transaction execute -z $DNS_ZONE
}

if [ x"$DNS_ZONE" == x"" ] ; then
	echo "Skipping dns setup: missing metadata."
	exit 1
fi

if [ x"$DNS_PROJECT" == x"" ] ; then
	export DNS_PROJECT="$(metadata 'project/project-id')"
fi
echo "Using project id: $DNS_PROJECT"

case $1 in
	start)	 replace_dns A     $PUBLIC_IP ;;
	restart) replace_dns A     $PUBLIC_IP ;;
	stop)	 replace_dns CNAME ghs.googlehosted.com. ;;
esac