Steering the evolution of a “legacy” software system is a difficult problem to solve. The size of the codebase, the high degree of coupling between components and the technical debt accumulated over the years can be overwhelming. Often, the lack of automated tests makes every technical change risky and potentially disruptive to the business. Think about customers not being able to place orders because of a library update.
How do teams approach this uncomfortable situation? When they are tasked with a major refactoring or migration exercise, how do they design a safe transition plan? How do they get started and measure progress?
In this post, we present a case study to show that a data-driven process, based on the Goal-Question-Metric method, can give clarity and confidence to the team. After introducing the approach, we describe some of the tools used to collect the data throughout the process (before and during the migration).