On-demand Virtualization for Post-copy OS Migration in Bare-metal Cloud

Abstract

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.