Hybrid cloud computing, where private and public cloud resources are combined and applications can migrate freely, ushers in unprecedented flexibility for businesses. To unleash the benefits, commercial products already enable the live migration of full virtual machines (CPU, memory, disk, network) between distant cloud datacenters. Unfortunately, no live migration progress management system exists, leading to (1) guesswork over how long a migration might take and the inability to schedule dependent tasks accordingly; (2) unacceptable application degradations – application components could become split over distant cloud datacenters for an arbitrary period during migration; (3) inability to balance application performance and migration time – e.g. to finish migration later for less performance interference. Pacer is the first migration progress management system. Pacer’s techniques are based on robust and lightweight run-time measurements of system and workload characteristics, novel efficient and accurate analytic models for progress predictions, and online adaptation to maintain user-defined migration objectives for coordinated and timely migrations.