Amazon Route 53 Dynamic DNS (CNAME) Updater Script

route53DynDNS.bash

#!/bin/bash
#
# This script requires xpath to parse part of the dnscurl.pl output
# on CentOS/RedHat/Amazon Linux:
#
# sudo yum install perl-XML-XPath
#
# also, dnscurl.pl (from http://aws.amazon.com/code/Amazon-Route-53/9706686376855511)
# expects your secrets to be in ~/.aws-secrets
# using a file format like this (from http://dmz.us/wp/wp-content/uploads/r53/aws-secrets.txt)
#
# %awsSecretAccessKeys = (
#    "my-aws-account" => {
#        id => "YOUR_ID_GOES_HERE_KEEP_THE_QUOTES",
#        key => "YOUR_SECRET_KEY_GOES_HERE_KEEP_THE_QUOTES",
#    },
# );


### User Settings (things you must set)

## Location of the dnscurl.pl script
DNSCurl="/path/to/route53DynDNS/dnscurl.pl"
## Zone/domain in which host (will) reside(s)
myDomainName="example.com"
## The host name you wish to update/create
myHostName=`hostname -f | sed -e "s/.$myDomainName//"`

##########################################

### Things you may want to set
## set the TTL for the new/updated A record
myTTL="60"
route53API="https://route53.amazonaws.com/2011-05-05"
route53APIDoc="https://route53.amazonaws.com/doc/2011-05-05/"

##########################################

### Thing you shouldn't change

## how long to wait after submitting a change
## before checking to see if it's state is
## INSYNC
sleepDelay=20

XPATH="xpath -e "
XPATH="xpath "

##########################################

### Code... don't change anything below.


## Get the Hosted Zone ID from Route 53
hostedZoneIDSearch="ListHostedZonesResponse/HostedZones/HostedZone[Name=\"$myDomainName.\"]/Id"
route53HostedZoneID=`$DNSCurl --keyname my-aws-account -- -s -H "Content-Type: text/xml; charset=UTF-8" -X GET $route53API/hostedzone 2>/dev/null | $XPATH $hostedZoneIDSearch 2>/dev/null |awk -F'[<|>]' '/Id/{print $3}' | cut -d/ -f3`

if [ -z $route53HostedZoneID ]; then
	echo "Could not find zone '$myDomainName' in route 53"
	exit 1
fi

## Check to see if the A record already exists
currentARecordValueSearch="ListResourceRecordSetsResponse/ResourceRecordSets/ResourceRecordSet[Name=\"$myHostName.$myDomainName.\"]/ResourceRecords/ResourceRecord/Value"

if [[ "$myHostName" == "*" ]]; then
  currentARecordValueSearch="ListResourceRecordSetsResponse/ResourceRecordSets/ResourceRecordSet[Name=\"\\052.$myDomainName.\"]/ResourceRecords/ResourceRecord/Value"
fi

currentARecordValue=`$DNSCurl --keyname my-aws-account -- -s -H "Content-Type: text/xml; charset=UTF-8" -X GET $route53API/hostedzone/$route53HostedZoneID/rrset 2>/dev/null | $XPATH $currentARecordValueSearch 2>/dev/null | awk -F'[<|>]' '/Value/{print $3}' | cut -d/ -f3`

## And if not, set a flag to create the A record
if [ -z $currentARecordValue ]; then
	echo "Could not find CNAME Resource Record for $myHostName.$myDomainName."
	echo "Creating initial record"
	CREATE_INITIAL=true
fi

## Route 53 updates require the A record name, ttl and value for the delete.
## Fetch the TTL
currentARecordTTLSearch="ListResourceRecordSetsResponse/ResourceRecordSets/ResourceRecordSet[Name=\"$myHostName.$myDomainName.\"]/TTL"

if [[ "$myHostName" == "*" ]]; then
  currentARecordTTLSearch="ListResourceRecordSetsResponse/ResourceRecordSets/ResourceRecordSet[Name=\"\\052.$myDomainName.\"]/TTL"
fi

currentARecordTTL=`$DNSCurl --keyname my-aws-account -- -s -H "Content-Type: text/xml; charset=UTF-8" -X GET $route53API/hostedzone/$route53HostedZoneID/rrset 2>/dev/null | $XPATH $currentARecordTTLSearch 2>/dev/null | awk -F'[<|>]' '/TTL/{print $3}' | cut -d/ -f3`

if [ -z $currentARecordTTL ]; then
	CREATE_INITIAL=true
fi

## Get the public Hostname
myPublicHostname=`wget -q -O - http://169.254.169.254/latest/meta-data/public-hostname`

if [ -z $myPublicHostname ]; then
	echo "Failed to look up public hostname"
	exit 1
fi

## Generate a timestamp for the update
timestamp=`date`

## Give some status
echo "Public hostname is: $myPublicHostname"

## If the DNS A Resource Record matched the public hostname, exit
if [[ "$myPublicHostname" == "$currentARecordValue" ]]; then
	echo "Current CNAME Resource Record address is: $currentARecordValue"
	echo "No need to update CNAME record."
	exit 0
fi

## Get a temp file
tmpxml=`mktemp`
#CREATE_INITIAL=false
## Determine if the A Resource Record is to be created or updated (deleted/created)
if [ $CREATE_INITIAL ]; then
echo "Creating CNAME record for $myHostName.$myDomainName. to be $myPublicHostname"
cat <<UPDATE-XML > $tmpxml
<?xml version="1.0" encoding="UTF-8"?>
<ChangeResourceRecordSetsRequest xmlns="$route53APIDoc">
	<ChangeBatch>
		<Comment>Create Record for $myHostName.$myDomainName at $timestamp</Comment>
		<Changes>
			<Change>
				<Action>CREATE</Action>
				<ResourceRecordSet>
					<Name>$myHostName.$myDomainName.</Name>
					<Type>CNAME</Type>
					<TTL>$myTTL</TTL>
					<ResourceRecords>
						<ResourceRecord>
							<Value>$myPublicHostname</Value>
						</ResourceRecord>
					</ResourceRecords>
				</ResourceRecordSet>
			</Change>
		</Changes>
	</ChangeBatch>
</ChangeResourceRecordSetsRequest>
UPDATE-XML

else
echo "A Record for $myHostName.$myDomainName. is $currentARecordValue with ttl: $currentARecordTTL"
echo "Updating CNAME record for $myHostName.$myDomainName. to be $myPublicHostname with ttl $myTTL"
cat <<UPDATE-XML > $tmpxml
<?xml version="1.0" encoding="UTF-8"?>
<ChangeResourceRecordSetsRequest xmlns="$route53APIDoc">
	<ChangeBatch>
		<Comment>Update Record for $myHostName.$myDomainName at $timestamp</Comment>
		<Changes>
			<Change>
				<Action>DELETE</Action>
				<ResourceRecordSet>
					<Name>$myHostName.$myDomainName.</Name>
					<Type>CNAME</Type>
					<TTL>$currentARecordTTL</TTL>
					<ResourceRecords>
						<ResourceRecord>
							<Value>$currentARecordValue</Value>
						</ResourceRecord>
					</ResourceRecords>
				</ResourceRecordSet>
			</Change>
			<Change>
				<Action>CREATE</Action>
				<ResourceRecordSet>
					<Name>$myHostName.$myDomainName.</Name>
					<Type>A</Type>
					<TTL>$myTTL</TTL>
					<ResourceRecords>
						<ResourceRecord>
							<Value>$myPublicHostname</Value>
						</ResourceRecord>
					</ResourceRecords>
				</ResourceRecordSet>
			</Change>
		</Changes>
	</ChangeBatch>
</ChangeResourceRecordSetsRequest>
UPDATE-XML
fi

## Do the actual create/update
updateResponse=`$DNSCurl --keyname my-aws-account -- -s -H "Content-Type: text/xml; charset=UTF-8" -X POST --upload-file $tmpxml $route53API/hostedzone/$route53HostedZoneID/rrset 2>/dev/null`
## And record the response
updateResponseStatus=`echo $updateResponse | $XPATH 'ChangeResourceRecordSetsResponse/ChangeInfo/Status' 2>/dev/null |awk -F'[<|>]' '/Status/{print $3}' | cut -d/ -f3`

## Make sure the response is "PENDING"
## Otherwise, error
if [[ "$updateResponseStatus" != "PENDING" ]]; then
	echo "Update is not in PENDING status"
	echo $updateResponse
	rm -f $tmpxml
	exit 1
fi

## Get the transaction ID
updateResponseID=`echo $updateResponse | $XPATH 'ChangeResourceRecordSetsResponse/ChangeInfo/Id' 2>/dev/null | awk -F'[<|>]' '/Id/{print $3}' | cut -d/ -f3`

echo "Got update status ID $updateResponseID with status $updateResponseStatus"
echo "Pausing $sleepDelay seconds to allow for sync"
sleep $sleepDelay

## Check for status
statusCheckResponse=`$DNSCurl --keyname my-aws-account -- -s -H "Content-Type: text/xml; charset=UTF-8" -X GET  $route53API/change/$updateResponseID 2>/dev/null`

statusCheckResponseStatus=`echo $statusCheckResponse | $XPATH 'GetChangeResponse/ChangeInfo/Status' 2>/dev/null | awk -F'[<|>]' '/Status/{print $3}' | cut -d/ -f3`

if [[ "$statusCheckResponseStatus" != "INSYNC" ]]; then
	echo "update failed!"
	echo "Status is $statusCheckResponseStatus"
	rm -f $tmpxml
	exit 1
fi

## Success, clean up
echo "Success!"
rm -f $tmpxml
exit 0