python - Heroku Flask Tutorial Procfile Meaning -

in heroku tutorial, there piece of code

hello.py

import os flask import flask  app = flask(__name__)  @app.route('/') def hello():     return 'hello world!' 

and procfile:

web: gunicorn hello:app --log-file=-

the part that's confusing hello:app part; hello refer hello() function or hello.py script? depending on meaning of that, whole procfile statement mean?

the procfile contains command line starting application on heroku. full documentation can found here: https://devcenter.heroku.com/articles/procfile

in case telling heroku use app variable (your constructed flask app) in hello module gunicorn , start web process (one can handle http requests). there other process types can specify such background workers.

your flask application object wsgi application, , can run using wsgi server. gunicorn 1 of choices on heroku.