[nine_k]

Boot time of a server is somehow important when you dynamically spin new instances. If spinning a new instance were a sub-second process, you could allow the number of instances you run (and pay for) to follow the demand much more closely.

But here the boot time is a proxy metric of complexity.

It's great to have software that can do a wide spectrum of things. But your server most often does a narrow spectrum of highly predefined tasks. You often go to great lengths to obviate and disallow any other activity on it, for security reasons.

So it would be great if you took the universal software, somehow cut it to your task set, and could throw away the unused parts (which are 90%+). Unfortunately, this is not really attainable with traditional OSes. Unikernels allow you to do just that—with some quite noticeable limitations, as of now, though.