Panels appearing in wrong position (end of web page) when serving a jupyter notebook with multiple processes

[olbermann]

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For defects or deficiencies, please provide ALL OF THE FOLLOWING:

ALL software version info (Panel, bokeh, python, notebook, OS, browser, any other relevant packages)

Python 2.7 on ubuntu 18.04,
Chromium and Firefox browsers
bokeh==1.3.4
jupyter==1.0.0
pandas==0.19.2
panel==0.6.2
tornado==5.1.1

Description of expected behavior and the observed behavior

In a notebook I generate a panel template and make it servable.
Then I run 'python -m panel serve sample.ipynb --num-procs 5'.

Now the first time I load the corresponding page the panels are included in the div
where they are supposed to appear. However, in a second browser or second tab
or after CTRL+R the panels are added to the bottom of the page instead of the position
in the expected div tag.

Am I doing something wrong or is this a bug?

Complete, minimal, self-contained example code that reproduces the issue

sample.ipynb:

import pandas as pd
import panel as pn
pn.extension()

dfs={}
panes = {}
for i in range(4):
    dfs[i]=pd.DataFrame(data=[[i,i],[i,i]])
    panes[i]=pn.Pane(dfs[i])

template_string = """
{% extends base %}
<!-- goes in body -->
{% block contents %}
<div class="container">
""" + "\n".join(["""
  <h2>Dataframe """ + str(pane_no) + """</h2>
  <div class="row">
    
    <div class="col-sm">
      {{ embed(roots.""" + "P" + str(pane_no) +
""") }}
    </div>
  </div>
""" for pane_no in panes]) + """
</div>
{% endblock %}
"""
template = pn.Template(template=template_string)
for pane_no in panes:
    template.add_panel("P" + str(pane_no), panes[pane_no])
template.servable()

command line:
python -m panel serve sample.ipynb --num-procs 5

Stack traceback and/or browser JavaScript console output

Screenshots or screencasts of the bug in action

[olbermann]

Same behaviour with
panel==0.6.4
bokeh==1.4.0
notebook==6.0.2
holoviews==1.12.6
pandas==0.25.3
python 3.7.3 on ubuntu 18.04, firefox

[philippjfr]

Thanks for reporting this, certainly quite bizarre.

[MarcSkovMadsen]

I have a similar problem. #897

[MarcSkovMadsen]

I've tried removing --num-procs 0 in my Dockerfile i.e. changing

ENTRYPOINT [ "panel", "serve", "app.py", "--address", "0.0.0.0", "--port", "80", "--num-procs", "0"]

to

ENTRYPOINT [ "panel", "serve", "app.py", "--address", "0.0.0.0", "--port", "80"]

and the problem goes away.

I've got this response on the gitter channel

When you connect to a bokeh server with an HTTP(S) request Bokeh returns a template, and that template immediately turns arounds and makes a websocket connection back to the Bokeh server. But with --num-procs > 1 there is no guarantee that the websocket connection lands on the same original process. That's why e.g. the full HTTP request is not available in the app code— if the websocket lands on a new process, that new process never saw the HTTP request, knows nothing about, can't even in principle provide it.

[philippjfr]

This will be fixed by changes in bokeh 2.0, so I've reassigned to the next major milestone which should coincide with bokeh 2.0.

[philippjfr]

This was fixed as part of Bokeh 2.0 and therefore Panel 0.9.