update-linode-dns-record

#!/bin/sh

usage(){
	fmt <<EOF
DESCRIPTION
	Check if the IP address of this host matches the DNS records of a remote host.  If it doesn't match, update the DNS records using the Linode API.

USAGE
	update-dns-record -h,--host=HOSTNAME -k,--api-key=LINODEAPIKEY -d,--domain-id=LINODEDOMAINID -r,--resource-id=LINODERESOURCEID
EOF
	exit
}
die(){ printf "Error: %s\n" "${1}" 1>&2; exit 1; }
require(){ command -v "${1}" > /dev/null 2>&1 || { suggestion=""; if [ ! -z "$2" ]; then suggestion=" $2"; fi; die "$1 is not installed.${suggestion}"; } }
if [ $# -eq 1 ]; then if [ "$1" = "--help" ] || [ "$1" = "-h" ]; then usage; fi fi
# End boilerplate

require "curl" "Try: apt-get install curl"

dynamicHost=""
linodeApiKey=""
domainId=""
resourceId=""

for i in "$@"
do
case "${i}" in
	-h=*|--host=*)
		dynamicHost="$(echo ${i} | sed 's/[-a-zA-Z0-9]*=//')"
	;;
	-k=*|--api-key=*)
		linodeApiKey="$(echo ${i} | sed 's/[-a-zA-Z0-9]*=//')"
	;;
	-d=*|--domain-id=*)
		domainId="$(echo ${i} | sed 's/[-a-zA-Z0-9]*=//')"
	;;
	-r=*|--resource-id=*)
		resourceId="$(echo ${i} | sed 's/[-a-zA-Z0-9]*=//')"
	;;
esac
done

if [ "${dynamicHost}" = "" ] || [ "${linodeApiKey}" = "" ] || [ "${domainId}" = "" ] | [ "${resourceId}" = "" ]; then
	usage
fi

# look up the existing dns entry
dnsIp=$(dig +short "${dynamicHost}")

if [ "${dnsIp}" = "" ]; then
	die "Could not resolve ${dynamicHost} while looking up DNS records."
fi

# look up our external ip
localIp=$(curl ifconfig.me 2> /dev/null)

if [ $? -ne 0 ]; then
	die "Could not resolve ifconfig.me while looking up local IP."
fi

if [ "${dnsIp}" != "${localIp}" ]; then
	curl "https://api.linode.com/?api_key=${linodeApiKey}&api_action=domain.resource.update&domainid=${domainId}&resourceid=${resourceId}&target=${localIp}" > /dev/null 2>&1

	if [ $? -ne 0 ]; then
		die "Could not connect to Linode API."
	fi
fi