Most legacy ETL estates weren’t designed. They grew over years, one urgent job at a time. In this session I share what I learned leading Ab Initio modernization programs at Discover and Capital One on AWS (EMR, Glue, PySpark): how we inventoried hundreds of jobs, decided what to rebuild and what to retire, and proved the new pipelines matched the old ones before turning anything off. These lessons don’t depend on the platform, and I’ll show how they translate to Fabric. You’ll leave with a practical playbook for running a migration without breaking downstream consumers.