Restric object to move on the surface of an other one

[Draco112358]

Hi all, I was wondering how to force an object (mesh) to move only on the surface of an other main one.
I've seen that they mostly implement a function using raycaster in order to detect collision and set object position.
In my case the main object has a complex geometry, so the manual setting of the position is very difficult.
Is there a component that make this task easyer, or the direct usage of raycast is the only way?
Thanks in advance to anyone who can help me.