Sounds like it doesn't need to be 100% reliable, though -- they have a painful backup system in place. Also, replaying traffic from the old system into the new

Sounds like it doesn't need to be 100% reliable, though -- they have a painful backup system in place. Also, replaying traffic from the old system into the new seems like a viable way to test out this sort of system. Or, they could have run both systems in parallel, and just sent a percentage of the traffic to the new system and slowly ramped up. I wonder why they chose to just cut over rather than doing a full and seemingly irreversible cutover. Not that many startups would have done things that way, since the nature of startups tends towards the green field. But plenty of more-established tech companies would have, I imagine.