gunicorn v20 : issue since the upgrade : Flask/Dash app Failed to find application object 'app.server' in 'index'

[Abdelkrim]

My app, based on Dash (https://plot.ly/dash/), stopped working after I updated my libraries by using https://pypi.org/project/pur

I didn't pay attention and gunicorn upgraded from v19.9.0 to v20.0.0.

There is clearly a breaking change but I don't know how to address it. Any thought?

PS: I have read this post but it didn't help me : https://github.com/benoitc/gunicorn/issues/2159

thank in advance for your help

The Error

Failed to find application object 'app.server' in 'index'
[INFO] Shutting down: Master
[INFO] Reason: App failed to load.

gunicorn command : working version if v19.9.0 but fails with v20.0.0

gunicorn --bind=0.0.0.0 --timeout 600 index:app.server

index.py

# -*- coding: utf-8 -*-
from dash.dependencies import Input, Output
from webapp import app
import dash_core_components as dcc
import dash_html_components as html
import logging
import os
import sys
from pages import (
    overview,
)

try:
    app.index_string = open(os.path.join("html", "index.html")).read()
except OSError:
    logging.exception("load (%d): index.html not found" %
                      sys.exc_info()[-1].tb_lineno)
    sys.exit()

# Describe the layout/ UI of the app
app.layout = html.Div([
    dcc.Location(id="url", refresh=False),
    html.Div(id="page-content")
])


# Update page
@app.callback(Output("page-content", "children"),
              [Input("url", "pathname")])
def display_page(pathname):
    if pathname == "/a-service/overview":
        return overview.layout
    else:
        return overview.layout


if __name__ == "__main__":
    app.run_server(debug=True, port=8051)

webapp.py

# -*- coding: utf-8 -*-
import dash

description = "a description"
title = "a title"
creator = "@altf1be"
app = dash.Dash(
    __name__,

    meta_tags=[
        {"name": "viewport", "content": "width=device-width, initial-scale=1"},
        {"name": "description", "content": description},
        {"name": "twitter:description", "content": description},
        {"property": "og:title", "content": description},
        {"name": "twitter:creator", "content": creator}
    ]
)
server = app.server
app.config.suppress_callback_exceptions = True

[benoitc]

can you start gunicorn with the debug level to see where the application is failing?

[r-chris]

Exact same issue here - I'll take a closer look soon

[Junnplus]

I think it related to this change: https://github.com/benoitc/gunicorn/commit/3701ad9f26a7a4c0a081dfd0f6e97ecb272de515#diff-0b90f794c3e9742c45bf484505e3db8dR377
same issue as: https://github.com/benoitc/gunicorn/issues/2159

[jamadden]

Try using a simple name instead of expecting gunicorn to traverse into objects. For example, webapp:server.

[mjclawar]

Try using a simple name instead of expecting gunicorn to traverse into objects. For example, webapp:server.

This also worked as a fix for me (changed gunicorn app:app.server to gunicorn app:server after adding a line to app.py that declared server = app.server)

[jakegt1]

I assume from now on this kind of thing will also never work:

gunicorn module.app:create_app()

[Abdelkrim]

Hi folks, here are the results of diverse attempts:

• index:app.server - module 'index' has no attribute 'app.server'
• index:app - Application object must be callable.
• index:app.layout - crashes
• index - AttributeError: module 'index' has no attribute 'application'

Still need to test those combinations:

• webapp:server
• index:server
• index.app:server

[benoitc]

@Abdelkrim with latest master?

[Abdelkrim]

@benoitc, I am running the v20.0.0 and not your latest update I am afraid

when will the latest update be available by using pip?

I do use Azure pipeline to deploy the web app and I don't know how to force the usage of the latest version of the code hosted on gituhub instead of using the regular requirements.txt

QUESTION: should I just wait a new version number? ... I'll deploy a new version of the code and give you my feedback (it requires ~1 hour => around 1:00am Brussels time)

[benoitc]

if you can test with the latest master that would help :) i will see if i reproduce it later this morning otherwise

[Abdelkrim]

@benoitc I can't access to the machine using ssh and force the usage of the latest version of gunicorn.

QUESTION : do you know how/when the latest release will be available on PyPi? I see this : Last released: Nov 9, 2019 on https://pypi.org/project/gunicorn

this will greatly facilitate my testing as I don't have access to any linux machine besides the Linux web apps on Azure :-(

Kind regards & thank you all for the time you have invested in this case

[benoitc]

@Abdelkrim the following commandline works:

gunicorn -w3 --pythonpath="/path/to/gunicorn/examples" deep.test:app

with the following example: https://github.com/benoitc/gunicorn/tree/master/examples/deep . I'm closing the issue then. The release will land today hopefully.

[Abdelkrim]

@benoitc thank you, I'm waiting for the latest release and I'll give you my feedback.

many thanks for your help

A.

[vytas7]

Confirmed fixed with the latest master, thanks!
(Although it wouldn't have been a big deal to adapt in our case if it was an architectural decision)

Edit: A fun fact, I happened to test with Git master just a couple of minutes before 20.0.1 hit PyPi :slightly_smiling_face:

[Abdelkrim]

@benoitc @davidism I wanted to thank you for the support. the app works using gunicorn v20