Xen Project Developer and Design Summit 2021

Unikernels research and development met an increasing interest in recent years because of the promising advantages offered to providers of cloud services. In contrast with mainstream deployments which usually involve a cloud application packaged in a general-purpose OS container, running the same application on top of a unikernel is obviously a much better choice considering the lower instantiation times and memory footprint. However, this approach enables a higher density of instances running on the same host and subsequently raises new challenges regarding efficient resource allocation. While initially unikernels were used for specialized applications, such as NFV or lightweight applications, now a major objective in unikernels development is porting existing applications with as little engineering effort as possible (e.g. Unikraft). One way to achieve this is to provide full POSIX compatibility, but some of the most popular cloud services were designed using fork() or cloning primitives to achieve higher performance or fault tolerance. This presentation proposes a solution based on Xen which addresses the concerns mentioned above by adding cloning support for unikernels. It tries to clarify the semantics of the fork() call for a unikernel and how it can be supported on a Xen environment by reusing as much as possible the available functionality in both hypervisor and toolstack.