On-Demand Virtualization for Post-Copy OS Migration in Bare-Metal Cloud

The demand for bare-metal cloud services has increased rapidly because bare-metal cloud is cost-effective for various types of cloud workloads. However, as the bare-metal cloud does not utilize the abstraction of the virtualization layer, it misses the benefits of virtualization. One important benefits absent in the bare-metal cloud is the live migration of guest operating systems. Migrating an OS and applications in the OS as a single unit provides a convenient way to manage cloud services such as load balancing, fault management, and system maintenance. To enable live migration for bare-metal cloud, several approaches have been proposed but they have limitations; they require OS modifications or impose additional overheads for workloads. This paper suggests an on-demand virtualization technique for post-copy OS migration to improve manageability of the bare-metal cloud services. When live migration is requested, a lightweight virtualization layer is enabled in the host on the fly. After completion of the live migration, the virtualization layer is removed from the host. Therefore, the host returns to a bare-metal system for performance. To implement on-demand virtualization, we modify BitVisor to perform the post-copy migration on the x86 architecture. The elapsed time of on-demand virtualization is negligible. It takes only 20 ms to insert the virtualization layer and 30 ms to remove the one. The downtime of migration is reduced because of the post-copy migration.