I have been watching a curious commit this week, which brought something called Metal to Rails. I had no idea what it was; I sort of get what Rack is supposed to do, and Metal builds on that. This post explains clearly though.

Metal is just a way of executing requests super-fast, without the full Rails stack loaded, but still inside your own code. You use it for tiny actions that need to run freaky fast. How fast? Twenty-five times faster than Rails fast. Yup, I get it now. I needed exactly this almost a year ago. Glad it’s here now though!