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Hi Sumit, responses inline.  Thanks,

Dan

On Tue, May 31, 2011 at 9:12 AM, Sumit Naiksatam (snaiksat) <
snaiksat at cisco.com> wrote:

> Hi Dan,
>
>
>
> Thanks for your prompt response on this.
>
>
>
> As I understand from your explanation, the knowledge of the “edge binding”
> resides with Nova, and in the case of my example that “edge binding” is
> “br100”. Is that correct? If so, how does Nova acquire this knowledge? I ask
> because, my expectation was that “br100” (i.e. the Linux bridge) is created
> and managed by Quantum (and/or the plugin underneath).
>

The way I see it, the "edge binding" is determined by Nova, then
communicated to Quantum.  It is the one bit of information that must be
shared across both systems.  Nova acquires this information as part of the
VM creation process.  For example, in the case of libvirt with type ethernet
on a linux system, nova would be the one creating the linux device that
represents the VM NIC.  It must then pass this edge binding of (device-name,
linux-system, interface-id) to Quantum, which must be running a plugin that
knows how to manage a vswitch on that linux host that can get/receive
packets from the linux device.


>
>
> Also, if we move away from using the interface type “bridge” (in the
> context of libvirt) to “ethernet” as you suggest, would that be the only
> “type” that would be supported? If so, that will not work with VN-Tag/VEPA
> since that requires a type “direct”. If we are indeed not limiting to just
> the “ethernet” type, then how does Nova know which type to use (assuming
> that the knowledge of the underlying network connectivity resides with
> Quantum)?
>

Our goal is to add more flexibility to the "vif plugging" portion of the
libvirt code to support multiple use cases, including both "ethernet" and
"direct".  In fact, VN-Tag/VEPA was one of the use cases we explored when
deciding on the model.  Based on my understanding of how libvirt handles
802.1Qbg, the libvirt XML includes a <virtualport> object that corresponds
to such a VM NIC and this virtual port includes parameters that identify the
VM, including a an "instanceid" parameter that globally represents the
virtual port.  I would expect that the "edge-binding" in this case would be
(instanceid, interface-id).  As a note, I have not actually used libvirt
like this on an actual VN-Tag/VEPA system.  If you are able to explore this
use case in more detail it would be great feedback for the Quantum design.



>
> It’s good to hear that the work on Quantum and Nova refactoring is going
> well. While that is in progress, it might be helpful to get some skeletal
> flowcharts (or even textual descriptions) describing the flows (with the
> interaction between Nova and Quantum fleshed out).
>

I agree that would be valuable.  We'll work on this.



>
>
> Thanks,
>
> ~Sumit.
>
>
>
> *From:* Dan Wendlandt [mailto:dan at nicira.com]
> *Sent:* Monday, May 30, 2011 11:15 PM
> *To:* Sumit Naiksatam (snaiksat)
>
> *Cc:* openstack at lists.launchpad.net
> *Subject:* Re: [Openstack] [NetStack] "Attach resource to port" semantics
>
>
>
> Hi Sumit,
>
>
>
> This is a great question to be asking, as it gets to the heart of how
> Quantum will work with Nova (or any any other OpenStack service that plugs
> into the network).  As you suggest, our goal here is to try and come up with
> a clean separation between the responsibilities of Nova and
> the responsibilities of Quantum.
>
>
>
> The way I think about it, the act of "attaching a VM NIC to the network"
> actually happens at two distinct layers: logical (managed by Quantum) and,
> for lack of a better name, non-logical (managed by Nova).
>
>
>
> Non-Logical: This occurs when the Nova spins up a VM and plugs the VM NIC
> into the vswitch.  For example, with Nova using libvirt, this amounts to
> creating a linux device representing the VM NIC (e.g., tap0) and associating
> it with a vswitch (e.g., br0).  With Quantum, this act alone should not
> actually cause the VM to be able to send and receive packets, unless the
> logical connectivity of the VM NIC has already been setup (see below).
>  Instead, it is just establishing a channel by which vswitch controlled by
> Quantum can pass packets to and from the VM NIC once the proper logical
> connectivity has been specified.  With Quantum, Nova must have an
> "interface-id" for each VM NIC.  When Nova spins up a VM and creates a new
> port on a vswitch, it communicates to Quantum the interface-id associated
> with that port on the vswitch.  We refer to as the "edge binding" (see
> slides #7 and #14 in
> http://www.slideshare.net/danwent/quantum-diablo-summary).
>
>
>
> Logical: This type of "plugging" is done by the tenant via the Quantum API.
>  The Quantum API exposes the concept of networks and ports on those networks
> to model this logical connectivity.  Interface-ids can be "attached" to a
> port, indicating the network connectivity that should be seen by the VM NIC
> with the associated interface-id (e.g., two VMs attached to ports on the
> same logical network can connect directly at L2, others cannot).  A simple
> implementation of a logical network could be to put implement each logical
> network as a different VLAN within a single physical L2 domain, with a
> Quantum plugin managing the vswitch to put each port on the appropriate VLAN
> (see slide #15).
>
>
>
> The motivation for this design is that Nova does not need to be involved
> when the logical connectivity of a VM changes. Nova just needs to worry
> about making sure the vswitch (or physical switch if using VNTag/VEPA)
> managed by the Quantum plugin has a channel to pass bits to and from each VM
> NIC, and knows the identify of each of those channels (the edge binding).
>  It is up to the Quantum plugin managing the vswitch to make sure the right
> logical connectivity (or lack thereof) is implemented.
>
>
>
> Along with folks from the Nova team, we've been discussing the details of
> how this model applies to different Nova "virt" layer implementations,
> including libvirt, XenServer, VMware, etc.  As you suggest, the libvirt
> model where Nova specifies only a bridge to connect to is less flexible, so
> we're looking at using an <interface> elements of type "ethernet" instead of
> type "bridge" as an alternative (Ryu did some work on this in a branch).
>
>
>
> Implementation work on an experimental version of Quantum has been
> progressing well, so in another week or two I would expect that we can have
> a full stack of code that people can play with using a slightly tweaked
> version of Nova.  Having this available will hopefully make the above
> description of a logical + non-logical plugging step more concrete and will
> serve as a good vehicle for feedback from the community.  Happy to chat more
> about this tomorrow at the Networking meeting on IRC.
>
>
>
> dan
>
>
>
>
>
>
>
> On Mon, May 30, 2011 at 9:01 PM, Sumit Naiksatam (snaiksat) <
> snaiksat at cisco.com> wrote:
>
> Hi,
>
>
>
> I would like to request clarity on the semantics of the "attach resource to
> port" operation proposed in Quantum in the context of spawning a VM. Let's
> discuss this with respect to a specific example. As of today, nova-compute
> generates the domain configuration (libvirt.xml), including the network
> interface configuration as below -
>
>
>
>         <interface type='bridge'>
>
>             <source bridge='br100'/>
>
>             <mac address='02:16:3e:78:4d:84'/>
>
>             <!--   <model type='virtio'/>  CANT RUN virtio network right
> now -->
>
>             <filterref filter="nova-instance-instance-00000001">
>
>                 <parameter name="IP" value="10.1.0.2" />
>
>                 <parameter name="DHCPSERVER" value="10.1.0.1" />
>
>                 <parameter name="PROJNET" value="10.1.0.0" />
>
>                 <parameter name="PROJMASK" value="255.255.255.128" />
>
>             </filterref>
>
>         </interface>
>
>
>
> By virtue of specifying "br100" as the bridge to connect to, nova-compute
> is configuring the attachment from the virtual NIC (on the VM) to the
> network, and the "attachment" operation is (implicitly) realized when the VM
> is spawned (and running).
>
>
>
> With the introduction of the "attach resource to port" operation, we are
> introducing an explicit step in the process of the VM spawning. It implies
> that prior to invoking the "attach resource to port" operation, nova-compute
> would not know which bridge to connect to (i.e. it would not know the
> identity of "br100"). So does nova-compute first spawn the VM without the
> network interface configuration? If that is the case, it brings us to the
> next question, which is, what does the "attach resource to port" operation
> actually do? There are at least two possibilities here -
>
>
>
> (1) The operation merely results in the identification (and, if required,
> the configuration) of "br100" as the bridge to connect the VM's network
> interface to. If that is the case, we need a way to propagate this
> information (i.e. "br100") back to the entity which invoked the "attach
> resource to port" operation. Subsequently, that same entity will have to
> perform another action to craft the VM's network interface configuration
> (with the acquired knowledge of "br100") and also add this network interface
> to the configuration of the VM (by making appropriate libvirt calls). Adding
> this network interface configuration could be done, both, prior to starting
> the VM, or even while the VM is running.
>
>
>
> OR
>
>
>
> (2) The operation not only identifies/configuration of "br100", but also
> crafts the VM's network interface configuration, and adds that interface to
> the VM (by making appropriate libvirt calls). Note that this second option
> amounts to Quantum controlling a resource on the VM (which ideally should be
> outside the scope of Quantum).
>
>
>
> OR, is it something else?
>
>
>
> Kindly let me know what you thoughts are on this. As projected above, these
> semantics have implications on how nova-compute will deal with spawning VMs
> (and it might be different from what it is today), and hence it might be
> important to address this issue sooner.
>
>
>
> Thanks,
>
> ~Sumit.
>
> PS: As I write this, it occurs to me that it's not very clear as to what
> the "create port" operation would do in the above case as well, since no
> actual port is created on the bridge. Any thoughts?
>
>
>
>
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>
>
>
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Dan Wendlandt
> Nicira Networks, Inc.
> www.nicira.com | www.openvswitch.org
> Sr. Product Manager
> cell: 650-906-2650
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~
>



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dan Wendlandt
Nicira Networks, Inc.
www.nicira.com | www.openvswitch.org
Sr. Product Manager
cell: 650-906-2650
~~~~~~~~~~~~~~~~~~~~~~~~~~~
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