How does Heroku and other managed services perform updates that might contain breaking changes? Or do they only perform minor updates or security updates with no breaking changes?
My biggest fear with managed hosting and managed databases is being given too short of a window before they update.
tl;dr: You get a few choices of Ubuntu LTS releases, which they maintain for a long time (currently they still support 14.04, now nearly 5 years old). Or you can push Docker images, at which point the underlying OS is squarely back in your court — technically they must be applying kernel patches, but Linus is fairly religious about not breaking userland.
My biggest fear with managed hosting and managed databases is being given too short of a window before they update.