datica_rails_app.rb

# routes.rb (checks if subdomains is present in the request object then sends it off to the correct location)
Rails.application.routes.draw do
  constraints MicrositeConstraint do
    root to: 'microsites#index', as: 'microsite_root'
  end
end

class MicrositeConstraint
  def self.matches?(request)
    taken = %w(
      api
      assets
      images
      www
    )

    request.subdomain.present? && !request.subdomain.in?(taken)
  end
end

# application_controller.rb (used in application to load the correct model based on the subdomain)
def current_microsite
  return unless request.subdomain.present? && request.subdomain != 'www'
  @microsite ||= Microsite.active.find_by!(host: request.subdomain)
end