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

[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(a)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(a)redhat.com&gt; 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(a)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(a)redhat.com&gt; > 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 :| >> _______________________________________________ >> Devel mailing list >> Devel(a)ovirt.org >> http://lists.ovirt.org/mailman/listinfo/devel >> > >