Due to the small memory footprint and fast startup times offerred by container virtualization, made ever more popular by the Docker platform, containers are seeing rapid adoption as a foundational capability to build PaaS and SaaS clouds. For such container clouds, which are fundamentally different from VM clouds, various cloud management services need to be revisited. In this paper, we present our Voyager-just-in-time live container migration service, designed in accordance with the Open Container Initiative (OCI) principles. Voyager is a novel filesystem-agnostic and vendor-agnostic migration service that provides consistent full-system migration. Voyager combines CRIU-based memory migration together with the data federation capabilities of union mounts to minimize migration downtime. With a union view of data between the source and target hosts, Voyager containers can resume operation instantly on the target host, while performing disk state transfer lazily in the background.