Of course it may vary a lot but i would say a hundred of thousands of users (100 000).
To explain the number, I assume a user will spend 1% of it's time on your app (that mean the average user spend around 15min per day (EVERY DAY) on your app, that may not sound impressive but it aldready is) and an nginx server on a powerfull machine could handle around 1k connection at the same time.
If you want to dig about an exemple of number far less abstract I remember stack overflow published their settings :
To explain the number, I assume a user will spend 1% of it's time on your app (that mean the average user spend around 15min per day (EVERY DAY) on your app, that may not sound impressive but it aldready is) and an nginx server on a powerfull machine could handle around 1k connection at the same time.
If you want to dig about an exemple of number far less abstract I remember stack overflow published their settings :
- https://nickcraver.com/blog/2013/11/22/what-it-takes-to-run-...
- https://nickcraver.com/blog/2016/02/17/stack-overflow-the-ar...
The 2013 article state they could handle 148,084,883 page load per day with a single database server (but they did use two) for exemple.