Operating system specialization is a well-known approach to optimize a specific application's performance, memory usage, security, or other important metrics. Specializing an OS for an application is typically a manual process that requires great expertise. Specialization through configuration lends itself well to automation; however, it is challenging due to the sheer size of the configuration space of modern OSes, the difficulty to quantify that space, the long time it takes to evaluate a configuration, and the large number of invalid configurations. Hence, existing attempts at specializing OSes automatically are limited to switching features on and off to minimize memory consumption or attack surface, and cannot target metrics such as performance.

At design time, modern operating systems are locked in a specific safety and isolation strategy that mixes one or more hardware/software protection mechanisms (e.g. user/kernel separation); revisiting these choices after deployment requires a major refactoring effort. This rigid approach shows its limits given the wide variety of modern applications' safety/performance requirements, when new hardware isolation mechanisms are rolled out, or when existing ones break.

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.

Increasingly, embedded devices are being equipped with ARM processors. Because of ease-of-use and widespread support for drivers and applications, Linux is often used as the OS of choice, even though it consumes a significant amount of the device's limited resources and its large attack surface presents opportunities for exploits. In this paper we propose Unikraft, a fully librarized operating system and build tool which allows for generating specialized OSes and software stacks targeting specific applications, while removing unneeded functionality. As a proof of concept, we port Unikraft to the Raspberry Pi 3 B+ and to a Xilinx Ultra96-V2. On these boards, Unikraft is able to boot in 88-158 milliseconds, consume only hundreds of KBs of memory when running real-world application such as NGINX, all the while providing visible reductions in power consumption compared to Linux distributions. Unikraft is an open source project and can be found at unikraft.org.