A patch proposal for multi-app setups

[Volodymyrk]

This patch address my question on SO
https://stackoverflow.com/questions/44744709/how-to-organise-a-plotly-dash-project

In order to serve multiple apps with one interpreter, I am using a DispatcherMiddleware from werkzeug.wsgi:
http://flask.pocoo.org/docs/0.12/patterns/appdispatch/

I'd like to avoid running multiple gunicorns on different ports, as this will complicate the setup unnecessary, IMO.

So my structure is as follows:

run.py

from werkzeug.serving import run_simple
from werkzeug.wsgi import DispatcherMiddleware

# importing apps
from index_app import app as app_ix
from app1 import app as app1
from app2 import app as app2
from app3 import app as app3

application = DispatcherMiddleware(app_ix, {
    '/app1': app1.server,
    '/app2': app2.server,
    '/app3': app3.server
})

# local debug
if __name__ == '__main__':
    run_simple('localhost', 5001, application)

and app1.py

import dash
import dash_core_components as dcc
import dash_html_components as html

from dash.dependencies import Input, Output
app = dash.Dash(app_path='/{}'.format(__name__))
...

Without my changes, however, individual apps don't know that they are served on a separate URL path and couldn't find resources, such as layout, etc.

Let me know if there is a better way to build a multi-page dash apps.

[Volodymyrk]

I believe that rc1405 solution in #70 is better .
However, if we want to allow the use of DispatcherMiddleware(), #70 alone is not enough.
Overall, feel free to Close this one - I wanted to start the conversation, hence proposed a dirty hack.