Re: Adopting CoreOS Ignition into Fedora+derivatives ecosystem

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----- Original Message -----
> From: "Colin Walters" <walters@xxxxxxxxxx>
> To: anaconda-devel-list@xxxxxxxxxx
> Sent: Friday, April 20, 2018 4:40:16 PM
> Subject: Re: Adopting CoreOS Ignition into Fedora+derivatives ecosystem
> A basic thing to keep in mind here is that the existing CoreOS didn't have
> kickstart
> and *only* has the PXE-to-Live model for bare metal (with optional persistent
> install), so there's
> a lot of overlap going on here.  But some of the technology makes sense and
> is obviously in use by the existing CoreOS community.  We're hoping to have
> a "best of both" message.
Yep, that definitely sounds like a good plan. :)

> We don't need to make any hard decisions here right away; the existing
> Fedora/Atomic and CoreOS will be maintained for a while, but we do
> hope to unify.
> On Tue, Apr 17, 2018, at 10:31 AM, Martin Kolman wrote:
> >
> > Yeah, Ignittion also seems to me like more like an enhanced Cloudinit
> > with some
> > installer bits bolted on & it indeed seems like it could work like a
> > good cloudinit replacement.
> One thing that only became a bit clearer to me recently is we actually
> still need:
> which handles the "processed every boot" aspect that one needs in
> many cloud environments; however the ignition ~= kickstart still remains,
> as well as the ssh-key/useradd type overlap between both of them
> and cloud-init/coreos-metadat.
> > Yeah, PXE-to-Live is pretty different to how Anaconda does,
> > we generally differentiate the installation environment and
> > the target system quite clearly and in this case they are basically
> > combined together. So if Ignition can do it it makes sense to
> > me to continu using it for this usecase, at least for the time being.
> Yeah, given that we don't have tooling that processes a kickstart
> at boot time.
Technically speaking, Initial Setup[0] does that - it reads the kickstart Anaconda generated
during installation and proceeds accordingly.

There are a couple expectations though:
- IS is run on the first boot of a system after installation (or on arm from pre-prepared image)
- the run is generally one-off and IS is disabled once it has done it's thing
- IS runs on the system after switchroot (eq. not in initrd)

I don't think there was ever a use-case considered where IS would run on every boot and act as a
system configuration agent.


> > I think that would work - would Anaconda be expected to parse the
> > content
> > of the section or would just writing the content to a file on the target
> > system
> > where Ignition will pick it up be enough ?
> This is a key question.  One thing that we're still discussing in the
> background
> is whether or not we *really* need ignition to be run in the initramfs or
> not for our primary use cases.  If we don't, a whole lot of things get
> simpler,
> it's much more like a better cloud-init that would still run earlier in the
> boot
> process (before /var is mounted ideally so you could dynamically configure
> local OS state, or potentially even replace /).
> I think for a lot of use cases just writing the file to the target system
> will be
> enough, so we don't need Anaconda integration immediately.  That said
> I haven't actually tried this yet.
BTW, we do regenerate initrd during installation so if you had Ignition as
a Dracut module, it could pick up the configuration file from the rootfs
when the initrd is regenerated.
(That's why we regenerate the initrd during installation - so that all packages 
and any configuration changes done by Anaconda are in place when Dracut generates
the initrd image.)

> > The git-like aproach rpm-ostree provides seems to me as a much more
> > advanced & flexible than just using the
> > relatively primitive and not very flexibile "you have two and exactly
> > two copies of everything" approach.
> Yeah; this is still being discussed because it has much higher level
> ramifications up the stack - the existing CoreOS updater has some
> sophisticated
> bits around the protocol for example.
Interesting! That's indeed more sophisticated than just a plain A/B system.

> But we're definitely aiming for "best of both" again.
Yet again sounds like a good plan. :)

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