Done by using the official php Docker image and installing the required packages.
If you don't know better, just download the example docker-compose file and copy it to whereever you want to use it. In that same folder create a "www" folder where you download all the Ranksystem files to. Use this command to start it up:
sudo docker compose up -d
Follow the rest of the Ranksystem install instructions - In your Browser go to http://--yourip--:8443/install.php and so on.