さくらのクラウドDNSを使ってダイナミックDNSサービス（DDNS）を自作する。

<?php

////===========================================================================================
//   *さくらのクラウドDNSでDDNSクラス
////===========================================================================================

class SakuraCloudDDNS{

	private $token = '';
	private $secret = '';

	public  $global_ip = '';
	public  $host_name = '';
	public  $ttl = 300;
	public  $dns_resource_id = '';
	public  $zone = 'is1a';
	public  $result_msg = '';
	public  $result_ary = [];

	///=======================================================================
	//   +__construct
	///=======================================================================

	public function __construct($p_token , $p_secret){

		$this->token = $p_token;
		$this->secret = $p_secret;
	}

	///=======================================================================
	//   +DDNS更新処理
	///=======================================================================

	public function DnsUpdate(){

		//---必要パラメータが空なら何もしない
		if($this->dns_resource_id === '' || $this->host_name === '' || $this->global_ip === ''){

			$this->result_msg = "設定不足です（dns_resource_id / host_name / global_ip）";
			return;
		}

		$json = $this->_apiGet("commonserviceitem/{$this->dns_resource_id}");

		$data = json_decode($json , true);

		if(is_array($data) && !empty($data["CommonServiceItem"]["Settings"]["DNS"]["ResourceRecordSets"])){

			$records = &$data["CommonServiceItem"]["Settings"]["DNS"]["ResourceRecordSets"];

			$updated = false;
			$found = false;

			foreach ($records as &$record){

				//---同一のホスト名のAレコードを選択
				if($record["Type"] === "A" && $record["Name"] === $this->host_name){

					$found = true;

					if($record["RData"] !== $this->global_ip){

						$record["RData"] = $this->global_ip;
						$record["TTL"]   = $this->ttl;

						$updated = true;
					}
				}
			}

			unset($record);

			if($found === false){

				$this->result_msg = "対象ホスト名のAレコードがありません（{$this->host_name}）";
				return;
			}

			//---IPアドレスが変わっているので更新する
			if($updated === true){

				$body = [
					"CommonServiceItem" => [
						"Settings" => [
							"DNS" => [
								"ResourceRecordSets" => $records,
							],
						],
					],
				];

				$result = $this->_apiPut("commonserviceitem/{$this->dns_resource_id}" , $body);

				//--- JSONを配列にデコード
				$res_ary = $this->result_ary = json_decode($result , true);

				if(is_array($res_ary) && !empty($res_ary["Success"]) && $res_ary["Success"] === true){

					$this->result_msg = "IP更新成功 ($this->global_ip)";

					file_put_contents("./latest_global_ip.txt" , $this->global_ip);

				} else{

					$this->result_msg = "IP更新失敗";
				}

			} else{

				$this->result_msg = "IP変更なし → 更新スキップ";
			}

		} else{

			$this->result_msg = "API取得失敗";
		}
	}

	///=======================================================================
	//   +_apiGet
	///=======================================================================

	private function _apiGet($p_path){

		$url = "https://secure.sakura.ad.jp/cloud/zone/{$this->zone}/api/cloud/1.1/{$p_path}";

		$ch = curl_init($url);

		curl_setopt($ch , CURLOPT_HTTPAUTH , CURLAUTH_BASIC);
		curl_setopt($ch , CURLOPT_USERPWD , $this->token . ":" . $this->secret);
		curl_setopt($ch , CURLOPT_RETURNTRANSFER , true);

		$result = curl_exec($ch);

		curl_close($ch);

		return $result;
	}

	///=======================================================================
	//   +_apiPut
	///=======================================================================

	private function _apiPut($p_path , $p_body){

		$url = "https://secure.sakura.ad.jp/cloud/zone/{$this->zone}/api/cloud/1.1/{$p_path}";

		$ch = curl_init($url);

		curl_setopt($ch , CURLOPT_HTTPAUTH , CURLAUTH_BASIC);
		curl_setopt($ch , CURLOPT_USERPWD , $this->token . ":" . $this->secret);
		curl_setopt($ch , CURLOPT_RETURNTRANSFER , true);
		curl_setopt($ch , CURLOPT_CUSTOMREQUEST , "PUT");
		curl_setopt($ch , CURLOPT_HTTPHEADER , [ "Content-Type: application/json" ]);
		curl_setopt($ch , CURLOPT_POSTFIELDS , json_encode($p_body));

		$result = curl_exec($ch);

		curl_close($ch);

		return $result;
	}
}

<?php

//---タイムゾーン
date_default_timezone_set('Asia/Tokyo');

//---相対PATHをセットする
chdir(dirname(__FILE__));

require("./_include/sakura_cloud_ddns.class.php");
require("./_include/config.inc.php");

//---------------------------------------------
//   *さくらクラウドDNSでDDNS更新 実行
//---------------------------------------------

$obj = new SakuraCloudDDNS(SAKURA_API_TOKEN , SAKURA_API_SECRET);

// 更新したいレコード名（ddns.xxxxxx.xxx ゾーンの中の "home"）
$obj->host_name = "home";

// さくらクラウドDNSのリソースID
$obj->dns_resource_id = DNS_RESOURCE_ID;

//---------------------------------------------
//   *グローバルIPの取得
//---------------------------------------------

//--- ipify から取得
$obj->global_ip = trim(file_get_contents("https://api.ipify.org"));

// テスト用：固定IPで強制上書きしたいときだけ使う
// $obj->global_ip = "1.1.1.1";

//---------------------------------------------
//   *DDNS更新実行
//---------------------------------------------

$obj->DnsUpdate();

echo $obj->result_msg;

file_put_contents("./latest_log.txt" , date("Y-m-d H:i:s") . "  {$obj->result_msg}");

<?php

echo $_SERVER['REMOTE_ADDR'];