[nderjung]

Hi, [disclaimer, I am a project maintainer].

The key difference between unikernels (and library OSes) vs. other kernels is that each kernel is different with a unikernel. Your application goes through a process of specialization, where you can decide exactly the necessary features (e.g. libraries, syscalls, memory allocation, scheduler, etc.) are necessary or desired for your application. Additionally, other kernels are typically multi-process whereas a unikernel is inherently single-process since it does not support syscalls like fork. (That said, at Unikraft, we are working on supporting fork, eta. late April).

Additionally, before Unikraft, one of the major trade-offs was developer time and effort to get your application into a unikernel. Since Unikraft has been actively developed for several years by ~100+ people, it has become much more stable, feature complete and easier to use; ultimately making unikernels easier to approach.

Today, in-addition to multi-process applications, the trade-off now really depends on your usecase and so selecting whether you wish to deploy your application as a unikernel or on top of a monolithic kernel or microkernel. For example, developer environments which require many subsystems, multiple programs, etc., where you can't know everything ahead-of-time, are still best suited for multi-user, monolithic kernels that can run most workloads.

Another thing to note is that unikernels are designed to be immutable and are often created in a CI/CD context. This means that they are single-purpose and if you wish to change them, you need to re-build (or re-package).