How I Built Klarna's Experimentation System, and a LISP
Klarna is "like Paypal, but in Europe, stronger on consumer, (probably) breaks more things, has too many official programming languages to count, and is allowed to be on the cloud. It's a tech jungle.". We had to introduce data driven decisions into an engineering process on a micro-service architecture layout. An experimentation platform that can work on N different languages (Java, Erlang and Haskell just to mention a few), has a <1ms overhead per call, no SPOF, extremely resilient, deployed on backends and frontends, had to be invented and then be built.
By one person.
This is a story about how I built it, and survived.