“Embrace Change”, says eXtreme Programming. Avoid big upfront design they said. What it means is to start experimenting with the knowledge we have at the time. Choose a potential solution (to a specific opportunity), and running experiments towards it.

When we do this, we very likely will learn that our assumptions were not 100% accurate - that is the whole point of the experiments. What if this means that some of the code is suboptimal, database structure is not supporting us the way we would wish they would. We send wrong kind of messages.

In the end, we need to live in the changing world. With changing codebase. If we live this assumption, we better learn how to evolve the codebase without breaking changes in prod. How to change the internal structure bit by bit in a way that every change is deployable to production with no breaking changes and that do not introduce bugs.

In this talk, Aki will introduce one possible strategy for such changes. Strategy he has used successfully in many projects and situations. The talk will explain how pattern of ‘expand-migrate-contract’ can be used in small scale (a function), in database migrations and all the way to behavior changes of event-driven microservices.