So we run a bunch of EventMachine at Stripe. I personally hate EventMachine, but it’s what we’ve got, and it’s probably the best answer if you really want async I/O in ruby. One question you inevitably find yourself asking the question: How close is my EventMachine worker process to capacity? How many more requests/second can this worker handle? This is, frustratingly, not a super straightforward question. Because of the asynchronous nature of EM, you might have multiple requests logic...
