function slack($message, $channel)
{
    $token = $_SERVER['TOKEN'];
    $ch = curl_init("https://slack.com/api/chat.postMessage");
    $data = http_build_query([
        "token" => $token,
        "channel" => $channel, //"#mychannel",
        "text" => $message, //"Hello, Foo-Bar channel message.",
        "username" => "ExternalHealthCheckBot",
    ]);
    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'POST');
    curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    $result = curl_exec($ch);
    curl_close($ch);

    return $result;
}

function healthCheck() {
    $url = $_SERVER['CHECK_URL'];
    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "GET");
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_HTTPHEADER,
            ['Content-Type: application/json']
    );
    $result =  curl_exec($ch);

    if (!curl_errno($ch)) {
        switch ($http_code = curl_getinfo($ch, CURLINFO_HTTP_CODE)) {
            case 200: #OK
                break;
            default:
                $str = json_encode(['code' => $http_code, 'response' => $result]);
                slack($str, 'check');
        }
    } else {
        slack(curl_error($ch), 'check');
    }

    curl_close($ch);
}

healthCheck();