I've found the idea of unikernels interesting for several years now, is there a tl;dr on why they don't seem to have taken off, like at all? Or is it all happening behind some doors I don't have access to?
They kind of did, that is basically how serverless works.
Managed runtimes on top of hypervisors.
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I think that part of it is that relatively few people use bare-metal servers these days, and nested virtualisation isn't universally supported. I also found this technical critique [0] compelling, but I have no idea if any of it is accurate or not.
[0]: https://www.tritondatacenter.com/blog/unikernels-are-unfit-f...