Which web server is my droplet using ? ubuntu 16.04)

I have a droplet using ubuntu 16.04. The use case is hosting and running some simple web apps.

I can deploy one instance of an app on :8080, working well. Deploying a second app, on another port, it will not work.

In order to trouble shoot this, I am searching for the server software running inside the droplet, which I cannot locate. (traditionally apache2 is used ?)

Am I missing something in the wider picture here ?

My goal is to set up a reverse proxy inside my droplet, and have it serve on a port per application setup.

Thanks for reading.