How can you make the id in the URL be random?

So I am looking for a way to create a randomized id that will link to a lobby that will be shown when the shown method is called in rails. As of right now, the url would look like this: http://localhost:3000/lobby/2. I'm looking to replace that 2 with a randomly generated id so you could send that link to friends if you want them to join your lobby. Any ideas?