With one big limitation: they must all run the same os kernel (so you cannot run say a Windows or FreeBSD container on a Linux host).

In fact, nobody guarantees that say Fedora will run on an Ubuntu-built kernel. Or even on a kernel from a different version of Fedora. So, IMO, anything other than running the exact same OS on host and in container is a hack.

> In fact, nobody guarantees that say Fedora will run on an Ubuntu-built kernel.

"nobody guarantees" just means that you can't externalize the work of trying it and seeing if it works. I don't think that's a huge loss, considering the space of all possible kernels, configuration switches, patches and distro packages is huge.

It's like refusing to use a hammer because nobody can assure you that hammer A was thoroughly tested with nail type B.

No, its like using a nailgun A with nails Y when it's only guaranteed to work with nails X. Or like using a chainsaw A with chain Y when it says you should use X. But hey, at least you are not trying to use nails on a chainsaw... ;-)

No. It's like shooting yourself in the face because your friend survived it.

> nobody guarantees

As long as the ABI is stable and you don't reach out to something that would have moved within /{proc,sys,whatevs}, you're good. [0]

[0]: https://en.wikipedia.org/wiki/Linux_kernel_interfaces

Measure the "much higher" before deciding. Especially after you apply solutions to reduce the memory and disk cost.

I'd say the "much higher" is nowadays a relic of the past.