It's impossible to iterate quickly on a product without a reliable, responsive CI system. At a certain point, traditional CI providers don't cut it. Last summer, Shopify outgrew its CI solution and was plagued by 20 minute build times, flakiness, and waning trust from developers in CI statuses. Now our new CI builds Shopify in under 5 minutes, 700 times a day, spinning up 30,000 docker containers in the process. This talk will cover the architectural decisions we made and the hard lessons we learned so you can design a similar build system to solve your own needs.