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Hi Stefan,

Thanks to bring this to the ML. This is an interesting approach I have
not play with Dracut a lot in the past but it definitely is a good thing
look at.

When we started osbuilder the idea was to show adopters that Kata
was able to boot with any OS as base (as long follow some requirements) 
and probably they adapt as needed or create their own tooling get Kata
working for them. After all this time I see that it is more value to
have just one tool that anyone can use and is flexible for developers
and linux distributions adoption. 

So I think would need more feedback from all the community and also
from linux distributions in general so we can have a solution that 
works better for all.

Here some question related with dracut usage:

1. Is it possible to build a disk image?
I think the answer is not. This is a feature that is still difficult
to be compatible with packaging but helps in memory usage if used with
DAX. So probably a nice feature to keep

2. Is it possible to have a custom rootfs with packages I want?
Today we require system + agent + iptables + chrony. But also
we support not having system but the agent as init. Also, users 
may want to add additional binaries in the future (to be part of the
official image or just for hacking). 



On Tue, May 07, 2019 at 11:41:12AM -0400, Stefan Hajnoczi wrote:
> Hi,
> Paolo Bonzini, Xu Wang, and I discussed using dracut
> (https://dracut.wiki.kernel.org/) to build a distro-friendly initramfs
> at the OpenStack Denver PTG.
> 
> I'm sharing a proof-of-concept for Fedora.  Other distros can probably
> follow a similar approach.
> 
> This process creates an initramfs from the host system using dracut.
> It's fast and produces a relatively small initramfs.  On my Fedora 30
> system the file size is 19 MB including kata-agent and it could probably
> be optimized further.
> 
> osbuilder is replaced with dracut, a tool that distro kernel packagers
> are familiar with.  I hope that this approach will make it easy and
> acceptable to package Kata Containers.

This is the major pro I can find of using this. The adoption will be
easier for linux distributions, we had a workaround Fedora to build the
image at post install but still got errors as for fedora the way to go
is to use the host kernel. For SUSE Marco used a custom feature of OBS
that is called kiwi. For Ubuntu we dont have any effort to get packages
but we  have snaps that have a bit more of freedom that traditional
packaging tools. So I would like to get more feedback from differed
linux distributions.
> 
> The scripts below build a kata-containers-initrd.img with systemd and
> the kernel modules from the host system.  The generic distro kernel is
> used in the sandbox VM, something that distro kernel packagers will be
> happy about since it keeps their test matrix unchanged.
> 
> The proof-of-concept code is available here:
> 
>   https://github.com/stefanha/agent/tree/fedora-dracut
> 
> To build the Kata sandbox VM initramfs:
> 
>   # make
>   # mkdir initramfs-overlay
>   # make DESTDIR=initramfs-overlay install
>   # make initrd
> 
> Edit /etc/kata-containers/configuration.toml so that
> hypervisor.qemu.kernel points to the host's vmlinuz and initrd points to
> the generated kata-containers-initrd.img file.
> hypervisor.qemu.kernel_params must contain
> systemd.unit=kata-containers.target so that kata-agent is launched upon
> sandbox VM boot.  Also set hypervisor.qemu.use_vsock to true.
> 
> Stefan