From a technical perspective it's a separate server that communicates with the database through various mechanisms (e.g. federate engine) but it's no different from e.g. multiple instance of mariadb being abstracted by a galera cluster into something that behaves like a single database from a client perspective.
Anyway, I'm seriously going to look into using this on a product for work, thanks for sharing & your work on this! We are in the process of triaging a few different features for a product in education (can chat more about it if your curious!), including some fairly bog-standard predictive text features. We are also trying to avoid strictly depending on any one proprietary PaaS, so this might just fit the bill!
We can chat more about it here or feel free to pick one of the many contact routes scattered around the thread :)
What's the name of the product? What does it do?