On Wed, Aug 26, 2015, at 05:09 PM, Josh Boyer wrote:
> Hi All,
> 
> I'm emailing my questions on the topic here as it seems to be the best
> Fedora focused place to discuss Atomic Host and kernel interaction.
> If that isn't the case, please point me to where you believe that is.

As jbrooks pointed out, there is also [email protected].

Regarding interaction, one thing I'd ask the Fedora kernel packaging
team to keep in mind whenever making any changes to the kernel.spec
is that ostree takes over kernel installation - we don't use the stuff in %post.
The atomic swap of the bootloader configuration is at the heart of the model.

Things work OK now, but just something to keep in mind.  

> I have two basic questions around the interaction of Atomic Host and
> the kernel.  The first is fairly straightforward: is there anything
> Atomic Host or the atomic toolset needs that the kernel does not
> provide today?  

So the ostree side is one thing, but beyond that for Docker, storage
and networking are big items.  I think conversations on storage for
containers are going on elsewhere, but just noting that.

> The second question is a bit more involved.  Atomic provides the nice
> ability for rollback across the entire OS tree.  However, that
> requires an atomic image to be spun for every instance of that tree.

I'd say:

"requires an new tree composed to be spun for updated kernels".

I use "image" for qcow2, installer ISO, PXE-to-Live etc.  The first
two support in place upgrades.

> That, naturally, means that whenever a new Atomic Host instance is
> spun it will use whatever kernel happens to be the latest in the
> Fedora release it is built from.  This means that one cannot leverage
> the nice side effect of being able to update the kernel independently
> of userspace.  (Which is also nice from a testing perspective when it
> comes to kernels and regressions.)

Yes, currently, but most limitations around that kind of thing go
away with https://github.com/projectatomic/rpm-ostree/pull/107/commits

> To my understanding, the only way to provide such testing would be to
> create Atomic Host images that only deviate from the official images
> in that they provide a new kernel. 

There's also support for updates-testing:
https://fedoraproject.org/wiki/QA:Updates_Testing#Using_it_with_Fedora_Atomic_22

> With a two week image release timeframe though, being able to use
> different kernels might be a good idea.  Does anyone have any thoughts
> around this topic and how to possibly accomplish such testing?  The
> only other idea I had was to spin the Atomic Host images containing
> the last 3 kernels in them, but I am not sure if choosing between them
> at boot is currently possible with multiple kernels installed.

Having multiple trees that differ only by kernel by default in a single image
is indeed possible.  It might be interesting to have updates-testing cloud
images generated that also have the non-updates-testing content or something
like that.

Finally of course, don't forget that composing trees is something one can
do locally too, it doesn't require magical rel-eng powers.  It is an investment
to set up, but for those with multiple machines where you want to synchronize
state, it could be worth the investment.
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