Uber had a monolith endearingly named "API" - which at the time comprised of the bulk of Uber's backend processing code. As this service was getting unwieldy to maintain - for scalability and a variety of reason - we launched on a journey to break this up into Microservices. Thus began "Project Darwin". Little did we realize what we were in for. Turns out that migrations are not easy, and take a long, long time. At Uber, the physical world depends on our service, and as such, we hold ourselves to a high standard for availability. That means when we build new systems, there are many phases of validating the new system before production traffic can be rerouted to it. With this talk, we hope to share our learning with you to help you when you undergo a large migration of your own!