How to migrate large volumes of API consumers safely and reliably

There are many reasons why systems are being deprecated. Legacy stack, critical issues that cannot be addressed, outdated API, cognitive and support burden, architectural mistakes, and many more.

I will present the case of migrating a complex API that evolved naturally, yet its legacy features were not deprecated. I will go through the architectural decisions, explaining the system's past and how the migration strategy was designed and implemented.

I’ll cover the following topics:
1. How API evolution can result in infeasibility of migration
2. How can we prepare for future migration right from the start
3. How to perform shadow migration to detect issues early, and
4. How to perform migrations at scale for hundreds of consumers.

Important note: this topic covers migration of internal APIs, not external