How can I use Rails routes to redirect from one domain to another?

My app used to run on foo.tld but now it runs on bar.tld. Requests will still come in for foo.tld, I want to redirect them to bar.tld.

How can I do this in rails routes?

Bit more modern approach:

constraints(host: 'www.mydomain.com') do
  get '/:param' => redirect('https://www.mynewurl.com/%{param}')
end