The infrastructure at Airbnb is not anywhere approaching that scale, but it is still large and growing fast. Curtis tells The Platform that Airbnb has around 5,000 EC2 instances running on AWS, most of them being reserved instances just to keep things simple. About 1,500 of those EC2 instances are deployed for the web-facing parts of its applications and the remaining 3,500 being used for various kinds of analytics and machine learning algorithms that drive the business. That ratio is interesting in and of itself, and it would not be surprising that as Airbnb grows, the amount of compute capacity dedicated to analytics and machine learning grows relative to the transaction processing portion of the business. The reason is simple: as more places become available on Airbnb and more people start using it, the challenge is not finding a place to rent, but finding the right place, one that satisfies both the renter and the host.