Running on the virtual machine is an instance of nginx that serves static files and acts as reverse proxy.

When connected to on port 80, using unencrypted HTTP, it serves the files in /var/www/nota-nossl.

When connected to on port 443, using encrypted HTTPS, it serves the files in /var/www/nota and will proxy requests to URLs below https://nota-cloud/api/ to the cloud API server.

This server is configured using the files in /etc/nginx and controlled using $ sudo systemctl restart nginx.

The API server serves the interactive part of the cloud app, it runs with the user id of the tutor user.

It is written in Python 3, using Bottle to perform the request routing and gevents to realize the event streaming. Gunicorn is used to deploy the server.

This server is controlled using $ systemctl --user restart nota_api.

The server expects data to be POSTed to the /api/log/<sensor> endpoints, where <sensor> is replaced by an arbitrary name for the sensor.

The request Body has to be JSON encoded and contain a “value” key with a float value ({ "value" : 10.0 }).

Such a request can be created like this, using HTTPie:

http POST https://nota-cloud/api/log/nota_2 value:=-2.0

The other important endpoint is /api/stream, which sends a history of the most recent sensor values and newly ariving ones as server sent events.

You can watch this stream using the command below:

curl https://nota-cloud/api/stream

The web app subscribes to the /api/stream using EventSource and plots a new point on a line diagram whenever an event is received using Chart.js.