As with most things, there is more than one way to do it. Push to the application server and hook it to your flask application using [uWSGI](http://flask.pocoo.org/docs/0.12/deploying/uwsgi/), for example.
Personally, I have an AWS instance running a Node.JS server on (blocked) port 8000, a Django uWSGI app on 8001, and a static resume site, all being reverse-proxy served by nginx. So I don't really see the advantages of Nginx Unit yet.
[Here's](https://www.digitalocean.com/community/tutorials/how-to-serv...) an old guide for running Flask with uWSGI and nginx on Ubuntu. There are several more recent, detailed instructions online.
Personally, I have an AWS instance running a Node.JS server on (blocked) port 8000, a Django uWSGI app on 8001, and a static resume site, all being reverse-proxy served by nginx. So I don't really see the advantages of Nginx Unit yet.