How does Readup figure in this? So far it's quite responsive, but I have no idea how many people use the platform beyond the frequent commenters.
Glad to hear it's responsive! Way more people read than comment, and likewise more lurk than read but even so the challenges with scale so far have been related to processing the amount of data that we're gathering instead of the amount of people we have to serve it to (this will almost certainly change one day soon!).
In the very early days our database was almost completely normalized and didn't have any non-primary key indexes. Once we hit around 250k articles (we're currently over 500k) the main home screen was taking a few seconds to load. Now we've got some cached columns, strategic indexes and materialized views to help keep things snappy.
We're using AWS and currently only running a single medium EC2 instance each for our web and API servers but they're behind load balancers and we're ready to throw more servers into the mix at a moment's notice if need be. I'm confident that we can scale on our own with the use of AWS and other "big tech" infrastructure.