How to use subdomains to represent sections?

I have a website that has 3 main sections:

1. Tickets
2. Company (About Us)
3. Admin

I would prefer to use subdomains for these sections:
tickets.whatever.com, company.whatever.com

This should be done with routes. You have to rewrite routes and
url_for a bit. And don't forget to set
ActionController::Base.session_options[:session_domain] to
".whatever.com"
I don't think in your case you'll benefit much from using subdomains,
but it's only up to to decide whether to spend decent amount of time
hacking ActionController::Routing to and
ActionView::Helpers::UrlHelper to map things back and forth, or rest
happy with default routing.

The problem though is that I need a specific set of controllers for each
section. I dont want to do tickets.whatever.com/tickets/some_controller.

Does it means 'tickets' is module in your setup, like in
Tickets::SomeTicketsController#action_on_ticket?
You don't need it anyway, TicketsController filled with tickets
related actions is enough.