Why do websites tend to slow down day by day? Why do people say "Ruby on Rails is slow"? This presentation is the story that we Cookpad are fighting against the problems. We rewrote whole codes of Cookpad.com by Ruby on Rails in 2008. Since then we've been had an aim that we keep the average response time be under 200 ms. In this presentation, I'll introduce ways to make websites fast using Rails based on our experiences. And I'll talk about how engineers who are responsible for site's performance should work in their company.