Hello,

To be on the safe side, before proceeding, make sure to create a Snapshot for your Droplet. After that, as you mentioned you need to install LAMP and then Wordpress. You can follow the steps on how to do that here:

https://www.digitalocean.com/community/tutorials/how-to-install-linux-apache-mysql-php-lamp-stack-ubuntu-18-04

In order to be able to run both services, you need to make sure that they are not running on the same port. For example if you already have your Ruby-on-Rails app running on port 80, Apache would not be able to start. To fix that what you could do is change the port that your Ruby-on-Rails app is running on a different port and then set up apache as a reverse proxy server to proxy the traffic to your rails app. Here’s how to do that:

https://www.digitalocean.com/community/tutorials/how-to-use-apache-as-a-reverse-proxy-with-mod_proxy-on-ubuntu-16-04

Regards,
Bobby