I am running a server with an old version of Debian, which needs to be upgraded. To do this, I want to replace this server with a new one, run both simultaneously, set up the new one and replace the old.
The old server is running Apache 2 for our forums, website, wiki etc. with PHP 5 and MySQL (and each with one subdomain e.g. forum.XXX.com, wiki.XXX.com etc). PHP 5 is "needed" because we got some legacy stuff that does not work on new versions of php (yet).
I thought about using PHP 5 and PHP 7, because as mentioned we need PHP 5 but we want to use some features for the new stuff, which requires PHP 7. With this in mind and the ability to e.g. update the server and still have the forums available, I thought about virtualization. But as far as i know, we only have 1 IP address.
Is this a "good" idea, or are there alternatives much better? My goal is to get the new server running with PHP 7 if possible. If not, I will stick with PHP 5 (on Debian 9?).
I am open for your suggestions and help for the idea mentioned above.