Probably a little late to be second-guessing exactly what happened there, but a few comments anyways: It's almost always worth doing some concurrency/scaling s

Probably a little late to be second-guessing exactly what happened there, but a few comments anyways: It's almost always worth doing some concurrency/scaling sanity checks on anything you're preparing to demo IME. There's plenty of ways any particular app, no matter what language or framework, could unexpectedly fall down when facing 20x traffic. If not from the language itself, perhaps from various external dependencies. It may be true, particularly at some previous times, that doing the most naive thing in Rails hosting was significantly worse than doing the most naive thing in Java hosting, but still, always worth checking. The 50ms DB round-trip 10x per request smells funny. Most queries to a closely located DB with demo app data should be more like 5ms or faster. Maybe there's good reason for it to take so long, I'm not sure. Perhaps the DB also had some slowdown from so many of those queries being executed concurrently, or maybe it would have if you had had a faster Rails setup or used Java instead. All the more reason to always test it and not just assume it'll be fine because Java should be fast. Each individual web request is still gonna be rather slow if it's gotta do multiple 50ms DB round trips. I don't know Java that well, but C# and Ruby both have pretty decent tools for making that IO concurrent in the scope of an individual request. You have to deliberately use it though, since only you know which queries actually depend on data from other queries. I've been working professionally with Rails for several years. If I was deploying such an app now, it'd be simple and fast to say, I suppose I'll serve it with Puma. 2 cores, so 2 processes. 5-10 threads per process is pretty normal, maybe make it 20 here since I expect a lot of time waiting on DB IO. Now we've got 40 workers and it ought to serve traffic from 20 users fine. Assuming some other part doesn't fall down first.