#!/usr/bin/php
<?php
/**
 * ELB Internal Route53 Updater
 * @author Cyril Aknine https://github.com/darylounet
 */

$vpcId = 'your-vpc-id';
$elbNetworkDescription = 'Your ELB network interface description (generated like "ELB your-elb-name")';
$route53InternalHostedZoneId = 'Your Route53 Internal hosted zone ID';
$route53InternalRecordName = 'your-route53-record.internal.'; // Ending with dot

$config = array(
    'credentials' => [
        'key'    => 'Your IAM Key',
        'secret' => 'Your IAM Secret',
    ]
    'region' => 'us-west-1'
);

/*
 * IAM Policy Requirements
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Stmt1462092886000",
            "Effect": "Allow",
            "Action": [
                "ec2:DescribeNetworkInterfaces"
            ],
            "Resource": [
                "*"
            ]
        },
        {
            "Sid": "Stmt1462092981000",
            "Effect": "Allow",
            "Action": [
                "route53:ChangeResourceRecordSets",
                "route53:ListResourceRecordSets"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}
*/

// http://docs.aws.amazon.com/aws-sdk-php/v3/download/aws.phar
require dirname(__FILE__) . '/aws.phar';

use Aws\Ec2\Ec2Client;
use Aws\Route53\Route53Client;

$ec2Client = new Ec2Client(array_merge($config, [ 'version' => '2015-10-01' ]));
$elbInterfaces = $ec2Client->describeNetworkInterfaces(array(
    'Filters' => array(
        array(
            'Name' => 'description',
            'Values' => [ $elbNetworkDescription ]
        ),
        array(
            'Name' => 'vpc-id',
            'Values' => [ $vpcId ]
        )
    )
));

$elbIps = array();
foreach ($elbInterfaces['NetworkInterfaces'] as $elbInterface) {
    $elbIps[] = $elbInterface['PrivateIpAddress'];
}
sort($elbIps);

$route53Client = new Route53Client(array_merge($config, [ 'version' => '2013-04-01', 'region' => 'us-east-1' ]));
$records = $route53Client->listResourceRecordSets(array(
    'HostedZoneId' => $route53InternalHostedZoneId,
    'StartRecordName' => $route53InternalRecordName
));

$route53elbIps = array();
foreach ($records['ResourceRecordSets'][0]['ResourceRecords'] as $record) {
    $route53elbIps[] = $record['Value'];
}
sort($route53elbIps);

// Check if Route53 update is needed
if ($elbIps === $route53elbIps) {
    die('Same Ips detected - no update needed'. PHP_EOL);
}

$route53ResourceRecords = array();
foreach ($elbIps as $ip) {
    $route53ResourceRecords[] = array('Value' => $ip);
}

$route53Client->changeResourceRecordSets(array(
    'HostedZoneId' => $route53InternalHostedZoneId,
    'ChangeBatch' => array(
        'Comment' => 'ELB Private IPs update',
        'Changes' => array(
            array(
                'Action' => 'UPSERT',
                'ResourceRecordSet' => array(
                    'Name' => $route53InternalRecordName,
                    'TTL' => 60,
                    'Type' => 'A',
                    'ResourceRecords' => $route53ResourceRecords
                )
            )
        )
    )
));