Update Route53 CNAME for an ec2 instance, from that instance

ec2_route53_update.sh

#!/bin/bash

# Ubuntu: Place this script in /var/lib/cloud/scripts/per-boot

HOST_CNAME=<CNAME to Update>
HOSTED_ZONE_ID=<Route53 Zone ID>

INSTANCE_ID=$(ec2metadata | grep 'instance-id:' | cut -d ' ' -f 2)
PUBLIC_HOSTNAME=$(ec2metadata | grep 'public-hostname:' | cut -d ' ' -f 2)

read -d '' DNS_CHANGE_JSON <<-_EOF_
{
  "Comment": "Update host",
  "Changes": [
    {
      "Action": "UPSERT",
      "ResourceRecordSet": {
        "Name": "$HOST_CNAME",
        "Type": "CNAME",
        "TTL": 60,
        "ResourceRecords": [
          {
            "Value": "$PUBLIC_HOSTNAME"
          }
        ]
      }
    }
  ]
}
_EOF_

aws route53 change-resource-record-sets --hosted-zone-id "$HOSTED_ZONE_ID" --change-batch "$DNS_CHANGE_JSON"