Migrating Instead of Building New

A migration is the work of moving the existing users of one system onto another while both systems keep running, until the old one can be removed. The users may be services, data, or, as at the marketplace, scheduled jobs. A migration is finished only when the old system is gone, not when the new one works.

For the scheduler project, building the new scheduler was the smaller part. The platform team could build it in about two quarters. Moving the 6,000 job definitions that 26 teams own, without a missed run or a double run along the way, was the larger and riskier part