I think there is no simple way to do it today as 'dupliframes' has been removed in 2.8. Or (and I hope) I am missing something...
So I don't see other solution than using hair particles to do it.
First, from your file:
You have at first steps several issues:
- Applying scales for curve and railing
- Removing rotation for the railing
- Place the railing at the origin of the curve
- Place the railing geometry above its origin
But just doing that you'll have:
and probably, you don't want that, but this:
Here you can think: ok, duplicate the rails manually... and maybe it is a good way to go if you have few rails.
However, to do it, you'll need to do the exact same thing but with a small surface, here a square, meaning using an array and a curve modifier.
But from that in order to handle the railing orientation, you'll add the railing as hair particles for the square with the following settings: