Welcome to your interview.
The question is on your right: Real-Time Experimentation Engine. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
How would you design a highly scalable, real-time experimentation engine for Optimizely that processes millions of events per second with minimal latency?