You'd be surprised. I know companies paying $2000+ a month for Heroku and are still having performance problems with Rails.
(Then again, they have them with Phoenix as well but to a lesser extent.)
Re:How to Fix Slow Code in Ruby
by jordanthoms on Thursday May 14, 2020 @09:57PM
(#23188016)
Yeah, Heroku performance on shared dynos is really not great. The variability is very high also, so you'll get some requests seemingly randomly timing out. The dedicated performance dynos are better, but even more expensive. We were on Heroku for a long time but as the scale got too much we migrated to Google Kubernetes Engine which has been great.
I've always thought of it as the platform you use for running toy apps with maybe a couple of dozen users at most and a low load. It's incredibly quick and easy to get a Rails app running on Heroku, a couple of hours at most. But you pay (in dollars and performance) for this.