config.ru

$LOAD_PATH.unshift(File.dirname(__FILE__))
require 'foo'

run Foo

foo.rb

require 'sinatra/base'
require 'redis'

class Foo < Sinatra::Base
  configure do
    set :redis, Redis.new
  end

  get '/' do
    settings.redis.incr 'counter'
    'foo'
  end

  get '/visits' do
    "#{settings.redis.get 'counter'} visits"
  end
end