Setup Flask on Ubuntu using Docker

I have created a flask app which works fine in development. However, when I launch this in production environment (using Gunicorn), I do not see updated code changes. For example, my index route returns Hello World when I first launch the server. Now if I change this to Hello World, How are you, and revisit the route, I still get Hello World.
I am confused as to why this might be happening. I need someone to set this up for me ASAP.