Plotly Backend Frontend working

I have been trying to read about how plotly (ggplotly) backend/frontend inner workings. In particular, I’m interested in how and where data is passed between client and server. I want to design an application that renders millions of points, and I understand there is a WebGL plugin. What I don’t understand is how and what data is passed from the server, even if plots can be rendered, it could be that data transfer is a bottleneck. I tried going through the plotly documentation but haven’t found the pertinent section with this information. Thank you very much!