We Migrated 200 CI/CD Pipelines. Zero Developers Complained. Zero Downtime.

200 CI/CD pipelines. Legacy platform to modern stack. Zero downtime. Zero developer disruption. Nobody even noticed the migration happened. That's not a failure of communication. That's the definition of success. The starting point: 22+ repositories, each with its own Jenkinsfile, its own quirks, its own tribal knowledge. Bitbucket pipelines that only the person who wrote them could debug - and that person had left six months ago. Every service a special snowflake. Every deployment a prayer. The goal was to replace all of that with a single 634-line universal pipeline template on GitLab CI. One file every service references. Change the template - every service gets the update. And a hard gate: 75% test coverage. Not optional, not negotiable. The migration strategy is what made it work. Eight services migrated in a specific sequence - dependencies first, consumers last. New pipelines ran alongside old ones for weeks before anyone was asked to switch. Automated parity checks compared outputs from old and new. If anything differed even slightly, investigation happened before migrating more. Any team could roll back with a single flag change. The timeline was "migrate when ready,"…