Allow serving Flask apps

[philippjfr]

Allows serving flask app using pn.serve, e.g.:

import panel as pn
from flask import Flask

flask_app = Flask(__name__)

@flask_app.route('/app')
def hello_world():
    return 'Hello, World!'

def panel_app():
    return "# This Panel app runs alongside flask, access the flask app at [here](./flask/app)"

pn.serve({'/flask': flask_app, 'panel': panel_app}, port=5001)

This will serve the panel app on localhost:5001/panel and the flask app on localhost:5001/flask/app.

[codecov]

Codecov Report

Merging #1215 into master will decrease coverage by 0.13%.
The diff coverage is 25.00%.

@@            Coverage Diff             @@
##           master    #1215      +/-   ##
==========================================
- Coverage   87.61%   87.48%   -0.14%     
==========================================
  Files         106      106              
  Lines       12574    12601      +27     
==========================================
+ Hits        11017    11024       +7     
- Misses       1557     1577      +20     

Impacted Files	Coverage Δ
panel/io/server.py	37.65% <25.00%> (-2.35%)	⬇️

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[MarcSkovMadsen]

Wow. As a potential user of this I would like to learn what the best deployment strategi is for different use cases.

Panel on Bokeh server?
Panel on Django server?
Panel on Flask server?
Panel on Voila server?

And can I run Panel, Flask and the tranquilizer api on all those servers? How will they perform? What are the pros and cons?

This raises many questions. Can I use all the Flask functionality? For example can I build advanced rest apis using Flask extensions with open api documentation? Can I serve dynamic files using Flask? Would it be a good idea to mix flask and panel to a large extent? Could I embed Panel apps in the Flask apps I serve? And how? And whats the architecture. Is the flask server running. Or is the flask app running on Tornado?

Running on multiple servers as well as in notebook is a super power. But currently not documented and experiences not shared.

Request: Some kind of documentation and examples. :-)

[philippjfr]

Yes, we have funded work to document deployment options, so it's definitely coming.

[jbednar]

As one specific point among many that need documentation, if you used @flask_app.route('/') above, would the flask app be at localhost:5001/flask? If so, that seems like a more suitable first example to me...

[philippjfr]

if you used @flask_app.route('/') above, would the flask app be at localhost:5001/flask? If so, that seems like a more suitable first example to me...

No that explicitly does not work, flask apps may only be served on a subpath.

[philippjfr]

Well it was certainly beyond my ability to route things, might give that another go.

[jbednar]

Ok, I now see that in the code "Flask apps must be served on a subpath.". Definitely needs explaining, then...

[pgierz]

This looks very very cool....looking forward to seeing some examples!

[nitrocalcite]

This is really cool! However, I also wanted to serve a Tornado app alongside panel; though I figured it was possible, I couldn't find any docs.

So, for future comers to this thread, you can pass extra Tornado RequestHandlers to the Bokeh server underlying Panel using the (undocumented) extra_patterns kwarg in pn.server or pane.show. You should set it to what you'd expect for a Tornado Application - a list of tuples that are (path, handler) or (path: str, handler: RequestHandler, handler_init_kwargs: dict).

[mvirus1996]

@philippjfr
Can you explain how to redirect in this integration.
I tried "redirect()" function of flask but not working.