i have been using vnstat for years. even before i wrote this article on vnstat
recently i wanted to see graphs and charts of the collected data. and i found vnstat-dashboard
as you can see its a simple yet beautiful design and automatically identifies all available interfaces.
then you can pck what kind of chart to view
and finally you can choose what kind of data to view
installation is simple. just clone the github repo and drop it into your webserver's public directory
and finally configure the config.php for vnstat location which you can get by running which vnstat