How to install newer PHP versions on our Debian 9 (Stretch) LAMP server in PHP-FPM mode (page 2)
On the first page of the description, we added the deb.sury.org repository to our system package manager, from which we installed all available PHP versions. On this page, we run these versions of PHP on the test server, which run the PHP code of our web pages in parallel but independently of each other.