# Using Voila to convert Jupyter notebooks into web application¶

## 1. Introduction to Voila¶

Volia is a program used to convert Jupyter notebooks into standalone web applications which can be shared with others. Voila supports interactive widgets provided by the ipywidgets package, which is largely used in the OSSCAR project.

The purpose of the Voila program is to render the selected notebook and enable real-time interaction with the included widgets.

## 2. Run Voila and Deploy a Web Application¶

### a. Run Voila locally¶

Voila can be deployed via a variety of platforms. Primarily, one can access the web pages locally by connecting to a “port” provided by all computers which allows such local hosting of web pages. The default port number is 8866. One can specify the port number with “–port”. There are two ways to use Voila locally.

• Run Voila as a Jupyter server extension:

One can access the web apps through the Jupyter server extension by inserting “/voila/render/” after the Jupyter base URL and before the notebook path:

localhost:8888/voila/render/your_notebook.ipynb

• Run Voila as standalone application:

One can also run Voila as a standalone application through the terminal:

voila --template=osscar --enable_nbextensions=True your_notebook.ipynb


### b. Deploying with Binder (mybinder.org)¶

Binder (mybinder.org) offers free cloud computing services to deploy Jupyter applications. We can deploy the web applications with Voila by calling the Voila server extension. One can follow the steps as listed below:

• In order to use Voila, one needs to first install the Voila python package. For the binder cloud deployment path, put the package name “voila” in the requirements.txt file.

• The voila Jupyter server extension is specified by prepending “voila/render” to the path of your Jupyter notebook.

Provide the URL to mybinder.org as shown below:

### c. Deploying on a dokku server¶

The disadvantage of using Binder is that the allocated cloud computing power is very limited and loading can take long time. Alternatively, we can deploy the apps on dokku servers. Dokku is a open source platform as a service, which supports voila deployment as web applications. One can set up their own dokku servers. Otherwise, there is a dokku server maintained by the Materials Cloud team. Here is the link for instructions on how to deploy a new tool at Materials Cloud.

https://github.com/materialscloud-org/issues/wiki/Contributing-a-new-tool

For deploying apps with Voila for a single notebook, we need set the Procfile file as:

web: voila —-port=$PORT —-no-browser your_notebook.ipynb  For multiple notebooks, one can put them in a folder and use Voila to host the whole folder as: web: voila —-port=$PORT —-no-browser your_folder/


In order to save the computing resources and prevent idling kernels, one can set the timeout to kill idle kernels as:

web: voila —-port=$PORT —-no-browser your_notebook.ipynb --MappingKernelManager.cull_interval=60 --MappingKernelManager.cull_idle_timeout=120  ## 3. Use the OSSCAR Voila template¶ We developed a Voila template (voila-osscar-template) for the OSSCAR project. The template has been released with PyPi. One can install it locally with pip: pip install voila-osscar-template  For delopying with Binder and Dokku platforms, One needs to put the “voila-osscar-template” into the requriments.txt file. For Binder, one also needs to specify the jupyter_config.json file in the GitHub repository. The content of this file is shown below: { "VoilaConfiguration": { "enable_nbextensions": true, "theme": "light", "template": "osscar" } }  Normally, we need to set the enable_nbextenions: true for using custom widgets like the “widget-periodictable”. The theme has two options, light and dark. For dokku, we can modify the Procfile file as: web: voila --template=osscar --VoilaConfiguration.enable_nbextensions=True --port=$PORT --no-browser your_notebook.ipynb


For multiple notebooks, this template (special feature) will redirect the starting page from “index.ipynb”. One can create the “index.ipynb” file to link all other notebooks. The relevant input to the dokku Procfile is shown below:

web: voila --template=osscar --VoilaConfiguration.enable_nbextensions=True --port=\$PORT --no-browser your_folder/