Unikernels gained an increasing interest in the recent years because they provide efficient resource allocation and high performance for cloud services by bundling the application with a minimal set of OS services in a guest VM. Although a unikernel is by design small and lightweight, fleets of unikernels based on the same image are not necessarily more efficient than containers because the latter can rely upon OS primitives for sharing memory. Futhermore, porting POSIX applications on top of unikernels brings a new challenge: what does fork() mean in the world of unikernels where there is memory isolation within a VM? Lacking fork() support significantly reduces the applicability of unikernels in popular cloud applications.

Unikernels are famous for providing excellent performance in terms of boot times, throughput and memory consumption, to name a few metrics. However, they are infamous for making it hard and extremely time consuming to extract such performance, and for needing significant engineering effort in order to port applications to them. We introduce Unikraft, a novel micro-library OS that (1) fully modularizes OS primitives so that it is easy to customize the unikernel and include only relevant components and (2) exposes a set of composable, performance-oriented APIs in order to make it easy for developers to obtain high performance.

Recent research has shown that unikernels, lightweight virtual machines tailored to specific applications, have great potential in terms of performance, tiny boot times, small memory consumption, and a reduced trusted compute base. Creating and optimizing them, however, is currently a painful, time-consuming process that often needs redoing for every application. With Unikraft, we introduce a system for automatically building unikernels that drastically reduces this time without negatively impacting performance.

Containers are in great demand because they are lightweight when compared to virtual machines. On the downside, containers offer weaker isolation than VMs, to the point where people run containers in virtual machines to achieve proper isolation. In this paper, we examine whether there is indeed a strict tradeoff between isolation (VMs) and efficiency (containers). We find that VMs can be as nimble as containers, as long as they are small and the toolstack is fast enough.