Cylc hub not loading cylc ui

gturek · December 2, 2024, 5:10pm

Hi there! I am trying to set up a cylc hub. I managed to get to the point of users being able to login but the cylc UI does not show, only a page that says “A Jupyter Server is running”. I am at a bit of a loss. There are no errors in the logs.
I am running version 5.2.1 of jupyterhub with “out of the box” configuration, using sudospawner.
Some pointers would be highly appreciated.
Cheers!
Gaby

hilary.j.oliver · December 3, 2024, 12:18am

Hi Gaby,

Are you starting it as cylc hub?

Have you read the Jupyter docs on how to do that?
Run JupyterHub without root privileges using sudo — JupyterHub documentation

Notably:

Note: Setting up sudo permissions involves many pieces of system configuration. It is quite easy to get wrong and very difficult to debug. Only do this if you are very sure you must.
…
Since JupyterHub needs to spawn processes as other users, the simplest way is to run it as root, spawning user servers with setuid. But this isn’t especially safe, because you have a process running on the public web as root.
…
A more prudent way to run the server while preserving functionality is to create a dedicated user with sudo access restricted to launching and monitoring single-user servers.

It might be worth back-tracking to try running the hub as root on (e.g.) your own Linux box, to see how it should work.

If I do that, “out of the box” the server starts, and I can’t log in to it, but it prints a warning for the default PAM authenticator,

No allow config found, it’s possible that nobody can login to your Hub!
You can set c.Authenticator.allow_all = True to allow any user who can login to access the Hub,
or e.g. allowed_users to a set of users who should have access.

If then add the c.Authenticator.allow_all = True to $HOME/.cylc/uiserver/jupyter_config.py, I can log in with my system username and password, and everything works like a charm.

On logging in to the hub, it takes me straight to my Cylc UI, but I can get back to the Hub via the Cylc UI dashboard. The Hub Home page looks like this (clicking on My Server take me back to my Cylc UI):

The Hub Admin page looks like this:

I take it that page does not look like my screenshots above?

gturek · December 3, 2024, 9:06am

I was able to run as root without any issues. But this is not an acceptable solution on the server that will eventually host cylc_hub (mind you, using sudospawner is not a given either )
What I am getting when I login is a “plain” page:

Once I am there I am “stuck”, no way to log out even.
I am thinking that I am now missing some settings on the user side.
It’s not clear to me exactly what settings are required at the site and user level as described in UI Server Configuration — Cylc 8.3.4 documentation. I have a feeling that it is not working because (some of) those settings are missing.
As the test user, I have installed cylc-flow and cylc-uiserver.

oliver.sanders · December 3, 2024, 9:48am

Hi,

You appear to be running a vanilla Juypyter setup (this provides the hub and server model), however, you have not configured any apps for Jupyter to run. The hub and server are working, but with no apps to run, it will just show you the “A Jupyter Server is running” message.

We provide a Jupyter config for running the Cylc app which is activated automatically when you start the hub using the cylc hub command (this launches Jupyter Hub with the Cylc configuration). This is the recommended way to run the Cylc UI Server.

Alternatively, you can configure a vanilla Jupyter setup to run the Cylc app. This is how sites can add Cylc to pre-existing Jupyter Hub deployments. The config that the cylc hub command is defined in the file linked below, copy the relevant bits to your own Jupyter config and restart the service:

github.com

cylc/cylc-uiserver/blob/master/cylc/uiserver/jupyter_config.py

# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

# Configuration file for jupyterhub.

from pathlib import Path
import pkg_resources

This file has been truncated. show original

gturek · December 3, 2024, 9:57am

Aha, it may be a path issue maybe? Because the file is definitively there, in the python environment installation folder /home/cylc/.conda/envs/cylc/lib/python3.9/site-packages/cylc/uiserver
I added two lines to it:
c.Authenticator.delete_invalid_users = True
c.JupyterHub.spawner_class = ‘sudospawner.SudoSpawner’ (replacement)

Mind you, it must see that file, because it knows to use sudospawner

oliver.sanders · December 3, 2024, 10:26am

If you’re using sudospawner, then I think you either need to:

Modify the command sudospawner runs (what we do)

Get the sudospawne to run the cylc hubapp command (i.e. launch a Cylc server rather than a vanilla Jupyter server with no apps installed).

We use:
```
#!/bin/bash -l
exec ${0%/*}/path/to/env cylc hubapp
```
GitHub - jupyterhub/sudospawner: Spawn JupyterHub single-user servers with sudo
Configure jupyter server to use any required Cylc config.

cylc/cylc-uiserver/blob/master/cylc/uiserver/jupyter_config.py

gturek · December 3, 2024, 12:09pm

Yes!!! That did it. Thank you soo much Oliver.

gturek · December 3, 2024, 3:52pm

Now I have another problem as a user. I can log in, and I see all my workflows, but I cannot play them. The error is:
Command failed: play - [Errno 2] No such file or directory: ‘cylc’

MetRonnie · December 3, 2024, 4:01pm

Are you using a wrapper script for Cylc? Installation — Cylc 8.3.4 documentation

gturek · December 4, 2024, 1:56pm

Wrapper worked! Thanx a bunch

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Cylc hub not loading cylc ui

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