How to implement a landing page while maintaining the structure of an existing site?

Question

PHP

There is an old site on self-written cms. A new one is being developed. We designed and made up the landing page to put it on the old site instead of the main one. The main task is to preserve the structure of the old site.
It turns out that if the landing page is index.html, and the main page of the old site is index.php, I tell Apache to open it on request to the index.html domain. The link from the landing page to the old site leads to example.com/index.php. The old site, of course, opens, but the inside, of course, is completely collapsing.
Question. How to do it right? Is it possible to destroy Apache or Enginx?

Answer 1

<?php
if (!$_SERVER['REQUEST_URI'] or ($_SERVER['REQUEST_URI']=='/')) {
echo file_get_contents("./index.html");
exit();
}
Something like this, at the very beginning of your index.php add - then if only the main page opens, then the index.html file will be given (in the same folder with index.php or write your path), if this is not the main one, then it will be work out the old cms

Answer 2

look towards cms Status-X
any design can be embedded in 30 minutes ^ ^
..by the way, there will be a fork of this cms from me soon