update-route53-A.json

{
  "Comment": "Update the A record set",
  "Changes": [
    {
      "Action": "UPSERT",
      "ResourceRecordSet": {
        "Name": "MY_DNS_RECORD_NAME",
        "Type": "A",
        "TTL": 60,
        "ResourceRecords": [
          {
            "Value": "127.0.0.1"
          }
        ]
      }
    }
  ]
}

update53-EC2Pub.sh

#!/bin/sh

if [ -z "$1" ]; then 
    echo "IP not given...trying EC2 metadata...";
    IP=$( curl -s http://169.254.169.254/latest/meta-data/public-ipv4 )  
else 
    IP="$1" 
fi 
echo "IP to update: $IP"

HOSTED_ZONE_ID=$( aws route53 list-hosted-zones-by-name | grep -B 1 -e "YOUR_PARENT_DOMAIN_NAME" | sed 's/.*hostedzone\/\([A-Za-z0-9]*\)\".*/\1/' | head -n 1 )
echo "Hosted zone being modified: $HOSTED_ZONE_ID"

INPUT_JSON=$( cat /home/ec2-user/update53/update-route53-A.json | sed "s/127\.0\.0\.1/$IP/" )

# http://docs.aws.amazon.com/cli/latest/reference/route53/change-resource-record-sets.html
# We want to use the string variable command so put the file contents (batch-changes file) in the following JSON
INPUT_JSON="{ \"ChangeBatch\": $INPUT_JSON }"

aws route53 change-resource-record-sets --hosted-zone-id "$HOSTED_ZONE_ID" --cli-input-json "$INPUT_JSON"