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Cylc UI Server

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Cylc UI Server

This project contains the Cylc UI Server which serves the Cylc UI and communicates with running Cylc Schedulers. It also bundles the GUI.

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The functionality in this repository is required to run the Cylc web user interface.

This repository provides the following components of the Cylc system.

  • The UI

    This is the Cylc web app that provides control and monitoring functionalities for Cylc workflows.

    The UI is developed in a separate repository

  • The UI Server

    This is a web server which serves the Cylc web UI. It connects to running workflows and workflow databases to provide the information the UI displays. It is a Jupyter Server.

  • The Hub

    In multi-user setups this launches UI Servers, provides a proxy for running server and handles authentication. It is a JupyterHub server.


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For more information on the Cylc components and full-stack Cylc installations see the Cylc documentation.

For Single-User Setups

Via conda (preferred):

conda install cylc-uiserver

Via pip:

pip install cylc-uiserver

For Multi-User Setups

Via conda (preferred):

conda install cylc-uiserver-hub

Via pip (consult jupyterhub documentation):

pip install cylc-uiserver[hub]


The Cylc UIServer is a Jupyter Server extension (like JupyterLab).

For Single-User Setups

Run as a standalone server using a URL token for authentication:

# launch the Cylc GUI and open a browser tab
$ cylc gui

# alternatively the same app can be opened with the jupyter command
$ jupyter cylc

By default, authentication is provided by the URL token. Alternatively, a password can be configured (see Jupyter Server docs).

There is no per-user authorisation, so anyone who has the URL token has full access to the server.

For Multi-User Setups

Run a central JupyterHub server under a user account with the privileges required to spawn cylc processes as other users.

# launch the Cylc Hub
# (the default URL is http://localhost:8000)
$ cylc hub

Users then authenticate with the hub which launches and manages their UI Server.



The Cylc Hub will load the following files in order:

  1. System Config

    These are the Cylc defaults which are hardcoded within the repository.


  2. Site Config

    This file configures the Hub/UIS for all users. The default path can be changed by the CYLC_SITE_CONF_PATH environment variable.


  3. User Config

    This file


Alternatively a single config file can be provided on the command line.

cylc hub --config


If specifying a config file on the command line, the system config containing the hardcoded Cylc default will not be loaded.


The hub can also be run using the jupyterhub command, however, you must source the configuration files manually on the command line.

See the JupyterHub documentation for details on configuration options.

UI Server

See the Cylc documentation for all Cylc-specific configuration options.

The Cylc UI Server is a Jupyter Server extension. Jupyter Server can run multiple extensions. To control the extensions that are run use the ServerApp.jpserver_extensions configuration, see the Jupyter Server configuration documentation.

By default the Cylc part of the UI Server log is written to ~/.cylc/uiserver/uiserver.log.


The UI can be configured via the "Settings" option in the Dashboard.

Currently these configurations are stored in the web browser so won't travel around a network and might not persist.


Contributors Commit activity Last commit

Contributions welcome:

  1. Install from source into your Python environment:

    pip install -e .[all]


    If you want to run with a development copy of Cylc Flow you must install it first else pip will download the latest version from PyPi.

  2. For UI development follow the developer instructions for the cylc-ui project, then set the following configuration so Cylc uses your UI build (rather than the default bundled UI build):

    # ~/.cylc/uiserver/
    c.CylcUIServer.ui_build_dir = '~/cylc-ui/dist'  # path to build

Note about testing: unlike cylc-flow, cylc-uiserver uses the pytest-tornasync plugin instead of pytest-asyncio. This means you should not decorate async test functions with @pytest.mark.asyncio.

Copyright and Terms of Use

Copyright (C) 2019-2023 NIWA & British Crown (Met Office) & Contributors.

Cylc 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.

Cylc 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 Cylc. If not, see GNU licenses.

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