On Sun, Nov 11, 2012 at 09:46:43AM -0500, Alon Bar-Lev wrote:
> ----- Original Message -----
> > From: "Dan Kenigsberg" <dan...@redhat.com>
> > To: vdsm-de...@fedorahosted.org
> > Sent: Sunday, November 11, 2012 4:07:30 PM
> > Subject: [vdsm] Future of Vdsm network configuration
> > 
> > Hi,
> > 
> > Nowadays, when vdsm receives the setupNetowrk verb, it mangles
> > /etc/sysconfig/network-scripts/ifcfg-* files and restarts the network
> > service, so they are read by the responsible SysV service.
> > 
> > This is very much Fedora-oriented, and not up with the new themes
> > in Linux network configuration. Since we want oVirt and Vdsm to be
> > distribution agnostic, and support new features, we have to change.
> > 
> > setupNetwork is responsible for two different things:
> > (1) configure the host networking interfaces, and
> > (2) create virtual networks for guests and connect the to the world
> > over (1).
> > 
> > Functionality (2) is provided by building Linux software bridges, and
> > vlan devices. I'd like to explore moving it to Open vSwitch, which
> > would
> > enable a host of functionalities that we currently lack (e.g.
> > tunneling). One thing that worries me is the need to reimplement our
> > config snapshot/recovery on ovs's database.
> > 
> > As far as I know, ovs is unable to maintain host level parameters of
> > interfaces (e.g. eth0's IPv4 address), so we need another
> > tool for functionality (1): either speak to NetworkManager directly,
> > or
> > to use NetCF, via its libvirt virInterface* wrapper.
> > 
> > I have minor worries about NetCF's breadth of testing and usage; I
> > know
> > it is intended to be cross-platform, but unlike ovs, I am not aware
> > of a
> > wide Debian usage thereof. On the other hand, its API is ready for
> > vdsm's
> > usage for quite a while.
> > 
> > NetworkManager has become ubiquitous, and we'd better integrate with
> > it
> > better than our current setting of NM_CONTROLLED=no. But as DPB tells
> > us,
> > https://lists.fedorahosted.org/pipermail/vdsm-devel/2012-November/001677.html
> > we'd better offload integration with NM to libvirt.
> > 
> > We would like to take Network configuration in VDSM to the next level
> > and make it distribution agnostic in addition for setting the
> > infrastructure for more advanced features to be used going forward.
> > The path we think of taking is to integrate with OVS and for feature
> > completeness use NetCF, via its libvirt virInterface* wrapper. Any
> > comments or feedback on this proposal is welcomed.
> > 
> > Thanks to the oVirt net team members who's input has helped writing
> > this
> > email.
> Hi,
> As far as I see this, network manager is a monster that is a huge dependency
> to have just to create bridges or configure network interfaces... It is true
> that on a host where network manager lives it would be not polite to define
> network resources not via its interface, however I don't like we force network
> manager.
> libvirt is long not used as virtualization library but system management
> agent, I am not sure this is the best system agent I would have chosen.
> I think that all the terms and building blocks got lost in time... and the
> result integration became more and more complex.
> Stabilizing such multi-layered component environment is much harder than
> monolithic environment.
> I would really want to see vdsm as monolithic component with full control over
> its resources, I believe this is the only way vdsm can be stable enough to be
> production grade.
> Hypervisor should be a total slave of manager (or cluster), so I have no
> problem in bypassing/disabling any distribution specific tool in favour of
> atoms (brctl, iproute), in non persistence mode.
> I know this derive some more work, but I don't think it is that complex to
> implement and maintain.
> Just my 2 cents...

I couldn't disagree more.  What you are suggesting requires that we reimplement
every single networking feature in oVirt by ourselves.  If we want to support
the (absolutely critical) goal of being distro agnostic, then we need to
implement the same functionality across multiple distros too.  This is more work
than we will ever be able to keep up with.  If you think it's hard to stabilize
the integration of an external networking library, imagine how hard it will be
to stabilize our own rewritten and buggy version.  This is not how open source
is supposed to work.  We should be assembling distinct, modular, pre-existing
components together when they are available.  If NetworkManager has integration
problems, let's work upstream to fix them.  If it's dependencies are too great,
let's modularize it so we don't need to ship the parts that we don't need.

Adam Litke <a...@us.ibm.com>
IBM Linux Technology Center

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