Running Flask apps inside ShinyProxy

In order to run Flask apps using ShinyProxy you have to consider two things:

• use a WSGI web server to run the Flask app (e.g., gunicorn, uWSGI). This means you cannot use the built-in server provided by Flask. Note that the developers of Flask advice to not use their built-in server for production usages. The Dockerfile in this repository illustrates how you can setup gunicorn for a very simple Flask application.

• ensure to use the url_for helper when referencing other pages and static files. The HTML files in the app/templates directory show the proper usage of the url_for helper. For example:

  <link rel="stylesheet" href="{{ url_for('static', filename='style.css') }}">
  <a href="{{ url_for('about') }}">About</a>
  <img width="400px" src="{{ url_for('static', filename='logo.png') }}">
  <script src="{{ url_for('static', filename='script.js') }}"></script>

Building the Docker image

To pull the image made in this repository from Docker Hub, use

sudo docker pull openanalytics/shinyproxy-flask-demo

The relevant Docker Hub repository can be found at https://hub.docker.com/r/openanalytics/shinyproxy-flask-demo.

To build the image from the Dockerfile, navigate into the root directory of this repository and run

sudo docker build -t openanalytics/shinyproxy-flask-demo .

ShinyProxy Configuration

Note: ShinyProxy 2.6.0 or later is required for running Flask apps.

Create a ShinyProxy configuration file (see application.yml for a complete file), containing:

proxy:
  specs:
    - id: flask-demo
      container-image: openanalytics/shinyproxy-flask-demo
      port: 8080
      container-env:
        SCRIPT_NAME: "#{proxy.getRuntimeValue('SHINYPROXY_PUBLIC_PATH').replaceFirst('/$','')}"
      target-path: "#{proxy.getRuntimeValue('SHINYPROXY_PUBLIC_PATH')}"

Note that the SCRIPT_NAME environment variable may not end with /, therefore we have to strip it from the variable.

References

• https://dlukes.github.io/flask-wsgi-url-prefix.html
• https://flask.palletsprojects.com/en/2.0.x/quickstart/#url-building
• https://gunicorn.org/
• Running FastAPI app in ShinyProxy

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