[dyndns]
aws_access_key_id = your_access_key_here
aws_secret_access_key = your_secret_key_here

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Stmt144999860000",
            "Effect": "Allow",
            "Action": [
                "route53:ChangeResourceRecordSets"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

mkdir dyndns && cd dyndns
composer require aws/aws-sdk-php monolog/monolog
touch index.php

<?php
	header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
	header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
 
	$credentialsPath = '/var/www/yoursite.com/.aws/credentials';
	$zoneId = 'your_zone_id';
	$recordName = 'home.yoursite.com.'; //The dot at the end is required
	$profile = 'dyndns';
	$ip = get_ip();
 
	require_once __DIR__.'/vendor/autoload.php';
 
	use Aws\Credentials\CredentialProvider;
	use Aws\Exception\CredentialsException;
	use Aws\Route53\Route53Client;
	use Aws\Route53\Exception\Route53Exception;
	use Monolog\Logger;
	use Monolog\Handler\StreamHandler;
 
	// Set up the logger - https://github.com/Seldaek/monolog
	$logger = new Logger('flyndns');
	$logger->pushHandler(new StreamHandler(
		__DIR__.'/flyndns.log', Logger::DEBUG
	));
 
	// If your web server runs under a different user to you, it won't
	// be able to read the ~/.aws/credentials file created with aws configure.
	// So specify the file to read manually.
	// https://serverfault.com/a/714220
	$provider = CredentialProvider::ini($profile, $credentialsPath);
	$provider = CredentialProvider::memoize($provider);
 
	// Set up the route 53 client - https://docs.aws.amazon.com/aws-sdk-php/v3/guide/getting-started/basic-usage.html#usage-summary
	$client = new Route53Client([
		'version' => 'latest',
		'region' => 'us-east-1', // route 53 requires this region
		'credentials' => $provider,
	]);
 
	try {
		// Do the DNS updating. Requires
		// - $recordName - e.g 'home.yourdomain.com.' Include the trailing dot character.
		// - $zoneId - the ID of your hosted zone
		// - $ip - Your new IP address. Change 'Type' below to 'AAAA' if using IPv6.
		//
		// https://docs.aws.amazon.com/aws-sdk-php/v3/api/api-route53-2013-04-01.html#changeresourcerecordsets
		// https://docs.aws.amazon.com/Route53/latest/APIReference/API_ChangeResourceRecordSets_Requests.html#API_ChangeResourceRecordSets_RequestBasicSyntax
		$result = $client->changeResourceRecordSets([
			'ChangeBatch' => [
				'Changes' => [
					[
						'Action' => 'UPSERT', // UPSERT will update or insert as required
						'ResourceRecordSet' => [
							'Name' => $recordName,
							'Type' => 'A', // Change to AAAA for ipv6
							'TTL' => 300,
							'ResourceRecords' => [
								[
									'Value' => $ip,
								],
								// ...
							],
						],
					],
				],
				'Comment' => 'DynDNS Home IP',
			],
			'HostedZoneId' => $zoneId,
		]);
	} catch (Route53Exception $e) {
		$logger->addError($e->getAwsErrorCode() . ': ' . $e->getMessage());
		exit("A '".$e->getAwsErrorCode()."' error occurred. Please check the log file for details.");
	} catch (CredentialsException $e) {
		$logger->addError("Invalid AWS credentials provided.");
		exit("Invalid AWS credentials provided: " . $e->getMessage());
	}
 
	$logger->addInfo("IP updated to " . $ip);
	exit("IP updated successfully. New IP: " . $ip);
 
	function get_ip()
	{
		$ip = '';
		if ( !empty($_SERVER['HTTP_X_FORWARDED_FOR']) )
			$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
		elseif ( isset($_SERVER['HTTP_CF_CONNECTING_IP']) )
			$ip = $_SERVER['HTTP_CF_CONNECTING_IP'];
		elseif ( isset($_SERVER['REMOTE_ADDR']) )
			$ip = $_SERVER['REMOTE_ADDR'];
 
		return $ip;
	}

if ( empty($_GET['code']) || $_GET['code'] != 'my_special_code' )
    exit;