https://devcenter.heroku.com/articles/stack https://devcenter.heroku.com/articles/stack tl;dr: You get a few choices of Ubuntu LTS releases, which they maintai

https://devcenter.heroku.com/articles/stack https://devcenter.heroku.com/articles/stack 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.