Got asked to design a rate limiter and blanked on where the state should even live

Sailed through the first two minutes, token bucket, fine, easy. Then they asked what happens with three instances behind a load balancer and I just... stopped. Redis felt like the obvious answer but I couldn't explain why in the moment, just said "shared state somewhere" like that meant anything. Looked it up after, it's not even that complicated, I just froze on air instead of thinking. Going to drill distributed-systems edge cases specifically now instead of assuming the core algorithm is the hard part.