[ovirt-devel] [kubevirt-dev] Re: [virt-tools-list] Project for profiles and defaults for libvirt domains

Sun Apr 8 12:35:12 UTC 2018

[resending to include OSP devs ]

YANIV LAVI

SENIOR TECHNICAL PRODUCT MANAGER

Red Hat Israel Ltd. <https://www.redhat.com/>

34 Jerusalem Road, Building A, 1st floor

Ra'anana, Israel 4350109

ylavi at redhat.com    T: +972-9-7692306/8272306     F: +972-9-7692223    IM: ylavi
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On Wed, Apr 4, 2018 at 7:23 PM, Yaniv Lavi <ylavi at redhat.com> wrote:

> [resending to include KubeVirt devs ]
>
> YANIV LAVI
>
> SENIOR TECHNICAL PRODUCT MANAGER
>
> Red Hat Israel Ltd. <https://www.redhat.com/>
>
> 34 Jerusalem Road, Building A, 1st floor
>
> Ra'anana, Israel 4350109
>
> ylavi at redhat.com    T: +972-9-7692306/8272306     F: +972-9-7692223    IM: ylavi
>  <https://red.ht/sig> TRIED. TESTED. TRUSTED. <https://redhat.com/trusted>
> @redhatnews <https://twitter.com/redhatnews>   Red Hat <https://www.linkedin.com/company/red-hat>   Red Hat <https://www.facebook.com/RedHatInc>
>
>
> On Wed, Apr 4, 2018 at 7:07 PM, Yaniv Lavi <ylavi at redhat.com> wrote:
>
>> Hi,
>> I'd like to go one step back and discuss why we should try to do this on
>> the high level.
>>
>> For the last 5-10 years of KVM development, we are pragmatically
>> providing the Linux host level APIs via project specific host
>> agents/integration code (Nova agent, oVirt host agent, virt-manager).
>> In recent time we see new projects that have similar requirements
>> (Cockpit, different automation tool, KubeVirt), this means that all of the
>> Linux virt stack consumers are reinventing the wheel and using very
>> different paths to consume the partial solutions that are provided today.
>>
>> The use of the Linux virt stack is well defined by the existing projects
>> scope and it makes a lot of sense to try to provide the common patterns via
>> the virt stack directly as a host level API that different client or
>> management consume.
>> The main goal is to improve the developer experience for virtualization
>> management applications with an API set that is useful to the entire set of
>> tools (OSP, oVirt, KubeVirt, Cockpit and so on).
>>
>> The Linux virt developer community currently is not able to provide best
>> practices and optimizations from single node knowledge. This means that all
>> of that smarts is locked to the specific project integration in the good
>> case or not provided at all and the projects as a whole lose from that.
>> When testing the Linux virt stack itself and since each project has
>> different usage pattern, we lose the ability to test abilities on the lower
>> level making the entire stack less stable and complete for new features.
>>
>> This also limits the different projects ability to contribute back to the
>> Linux stack based on their user and market experience for others in open
>> source to gain.
>>
>> I understand this shift is technically challenging for existing projects,
>> but I do see value in doing this even for new implementation like Cockpit
>> and KubeVirt.
>> I also believe that the end result could be appealing enough to cause
>> project like OSP, virt-manager and oVirt to consider to reduce the existing
>> capabilities of their host side integrations/agents to shims on the host
>> level and reuse the common/better-tested pattern as clients that was
>> developed against the experience of the different projects.
>>
>> I call us all to collaborate and try to converge on a solution that will
>> help all in the long term in the value you get from the common base.
>>
>>
>> Thanks,
>>
>> YANIV LAVI
>>
>> SENIOR TECHNICAL PRODUCT MANAGER
>>
>> Red Hat Israel Ltd. <https://www.redhat.com/>
>>
>> 34 Jerusalem Road, Building A, 1st floor
>>
>> Ra'anana, Israel 4350109
>>
>> ylavi at redhat.com    T: +972-9-7692306/8272306     F: +972-9-7692223    IM: ylavi
>>  <https://red.ht/sig> TRIED. TESTED. TRUSTED. <https://redhat.com/trusted>
>> @redhatnews <https://twitter.com/redhatnews>   Red Hat <https://www.linkedin.com/company/red-hat>   Red Hat <https://www.facebook.com/RedHatInc>
>>
>>
>> On Thu, Mar 22, 2018 at 7:18 PM, Daniel P. Berrangé <berrange at redhat.com>
>> wrote:
>>
>>> On Thu, Mar 22, 2018 at 03:54:01PM +0100, Martin Kletzander wrote:
>>> > >
>>> > > > One more thing could be automatically figuring out best values
>>> based on
>>> > > > libosinfo-provided data.
>>> > > >
>>> > > > 2) Policies
>>> > > >
>>> > > > Lot of the time there are parts of the domain definition that need
>>> to be
>>> > > > added, but nobody really cares about them.  Sometimes it's enough
>>> to
>>> > > > have few templates, another time you might want to have a policy
>>> > > > per-scenario and want to combine them in various ways.  For
>>> example with
>>> > > > the data provided by point 1).
>>> > > >
>>> > > > For example if you want PCI-Express, you need the q35 machine
>>> type, but
>>> > > > you don't really want to care about the machine type.  Or you want
>>> to
>>> > > > use SPICE, but you don't want to care about adding QXL.
>>> > > >
>>> > > > What if some of these policies could be specified once (using some
>>> DSL
>>> > > > for example), and used by virtuned to merge them in a unified and
>>> > > > predictable way?
>>> > > >
>>> > > > 3) Abstracting the XML
>>> > > >
>>> > > > This is probably just usable for stateless apps, but it might
>>> happen
>>> > > > that some apps don't really want to care about the XML at all.
>>> They
>>> > > > just want an abstract view of the domain, possibly add/remove a
>>> device
>>> > > > and that's it.  We could do that as well.  I can't really tell how
>>> much
>>> > > > of a demand there is for it, though.
>>> > >
>>> > > It is safe to say that applications do not want to touch XML at all.
>>> > > Any non-trivial application has created an abstraction around XML,
>>> > > so that they have an API to express what they want, rather than
>>> > > manipulating of strings to format/parse XML.
>>> > >
>>> >
>>> > Sure, this was just meant to be a question as to whether it's worth
>>> > pursuing or not.  You make a good point on why it is not (at least for
>>> > existing apps).
>>> >
>>> > However, since this was optional, the way this would look without the
>>> > XML abstraction is that both input and output would be valid domain
>>> > definitions, ultimately resulting in something similar to virt-xml with
>>> > the added benefit of applying a policy from a file/string either
>>> > supplied by the application itself.  Whether that policy was taken from
>>> > a common repository of such knowledge is orthogonal to this idea.
>>> Since
>>> > you would work with the same data, the upgrade could be incremental as
>>> > you'd only let virtuned fill in values for new options and could slowly
>>> > move on to using it for some pre-existing ones.  None of the previous
>>> > approaches did this, if I'm not mistaken.  Of course it gets more
>>> > difficult when you need to expose all the bits libvirt does and keep
>>> > them in sync (as you write below).
>>>
>>> That has implications for how mgmt app deals with XML. Nova has object
>>> models for representing XML in memory, but it doesn't aim to have
>>> loss-less roundtrip from parse -> object -> format. So if Nova gets
>>> basic XML from virttuned, parses it into its object to let it set
>>> more fields and then formats it again, chances are it will have lost
>>> a bunch of stuff from virttuned. Of course if you know about this
>>> need upfront you can design the application such that it can safely
>>> round-trip, but this is just example of problem with integrating to
>>> existing apps.
>>>
>>> The other thing that concerns is that there are dependancies between
>>> different bits of XML for a given device. ie if feature X is set to
>>> a certain value, that prevents use of feature Y. So if virttuned
>>> sets feature X, but  the downstream application uses feature Y, the
>>> final result can be incompatible. The application won't know this
>>> because it doesn't control what stuff virttuned would be setting.
>>> This can in turn cause ordering constraints.
>>>
>>> eg the application needs to say that virtio-net is being used, then
>>> virttuned can set some defaults like enabling vhost-net, and then
>>> the application can fill in more bits that it cares about. Or if
>>> we let virttuned go first, setting virtio-net model + vhost-net,
>>> then application wants to change model to e1000e, it has to be
>>> aware that it must now delete the vhost-net bit that virtuned
>>> added. This ends up being more complicated that just ignoring
>>> virttuned and coding up use of vhost-net in application code.
>>>
>>>
>>> > > This is the same kind of problem we faced wrt libvirt-gconfig and
>>> > > libvirt-gobject usage from virt-manager - it has an extensive code
>>> > > base that already works, and rewriting it to use something new
>>> > > is alot of work for no short-term benefit. libvirt-gconfig/gobject
>>> > > were supposed to be the "easy" bits for virt-manager to adopt, as
>>> > > they don't really include much logic that would step on
>>> virt-manager's
>>> > > toes. libvirt-designer was going to be a very opinionated library
>>> > > and in retrospective that makes it even harder to consider adopting
>>> > > it for usage in virt-manager, as it'll have signficant liklihood
>>> > > of making functionally significant changes in behaviour.
>>> > >
>>> >
>>> > The initial idea (which I forgot to mention) was that all the decisions
>>> > libvirt currently does (so that it keeps the guest ABI stable) would be
>>> > moved into data (let's say some DSL) and it could then be switched or
>>> > adjusted if that's not what the mgmt app wants (on a per-definition
>>> > basis, of course).  I didn't feel very optimistic about the upstream
>>> > acceptance for that idea, so I figured that there could be something
>>> > that lives beside libvirt, helps with some policies if requested and
>>> > then the resulting XML could be fed into libvirt for determining the
>>> > rest.
>>>
>>> I can't even imagine how we would go about encoding the stable guest
>>> ABI logic libvirt does today in data !
>>>
>>> >
>>> > > There's also the problem with use of native libraries that would
>>> > > impact many apps. We only got OpenStack to grudgingly allow the
>>> >
>>> > By native you mean actual binary libraries or native to the OpenStack
>>> > code as in python module?  Because what I had in mind for this project
>>> > was a python module with optional wrapper for REST API.
>>>
>>> I meant native binary libraries. ie openstack is not happy in general
>>> with adding dependancies on new OS services, because there's a big
>>> time lag for getting them into all distros. By comparison a pure
>>> python library, they can just handle automatically in their deployment
>>> tools, just pip installing on any OS distro straight from pypi. This
>>> is what made use of libosinfo a hard sell in Nova.
>>>
>>> The same thing is seen with Go / Rust where some applications have
>>> decided they're better of actually re-implementing the libvirt RPC
>>> protocol in Go / Rust rather than use the libvirt.so client. I think
>>> this is a bad tradeoff in general, but I can see why they like it
>>>
>>> Regards,
>>> Daniel
>>> --
>>> |: https://berrange.com      -o-    https://www.flickr.com/photos/
>>> dberrange :|
>>> |: https://libvirt.org         -o-
>>> https://fstop138.berrange.com :|
>>> |: https://entangle-photo.org    -o-    https://www.instagram.com/dber
>>> range :|
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>>>
>>
>>
>
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