Hi Sumit,<div><br></div><div>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. </div>
<div><br></div><div>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). </div>
<div><br></div><div>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 <a href="http://www.slideshare.net/danwent/quantum-diablo-summary">http://www.slideshare.net/danwent/quantum-diablo-summary</a>). </div>
<div><br></div><div>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). </div>
<div><br></div><div>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. </div>
<div><br></div><div>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). </div>
<div><br></div><div>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.</div>
<div><br></div><div>dan</div><div><br></div><meta charset="utf-8"><div><br></div><div><br><div class="gmail_quote">On Mon, May 30, 2011 at 9:01 PM, Sumit Naiksatam (snaiksat) <span dir="ltr"><<a href="mailto:snaiksat@cisco.com">snaiksat@cisco.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div lang="EN-US" link="blue" vlink="purple"><div><p class="MsoNormal"><span style="color:#1F497D">Hi,</span></p><p class="MsoNormal">
<span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">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 -</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D"> <interface type='bridge'></span></p><p class="MsoNormal"><span style="color:#1F497D"> <source bridge='br100'/></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> <mac address='02:16:3e:78:4d:84'/></span></p><p class="MsoNormal"><span style="color:#1F497D"> <!-- <model type='virtio'/> CANT RUN virtio network right now --></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> <filterref filter="nova-instance-instance-00000001"></span></p><p class="MsoNormal"><span style="color:#1F497D"> <parameter name="IP" value="10.1.0.2" /></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> <parameter name="DHCPSERVER" value="10.1.0.1" /></span></p><p class="MsoNormal"><span style="color:#1F497D"> <parameter name="PROJNET" value="10.1.0.0" /></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> <parameter name="PROJMASK" value="255.255.255.128" /></span></p><p class="MsoNormal"><span style="color:#1F497D"> </filterref></span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </interface></span></p><p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">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).</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">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 -</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">(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.</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">OR </span></p><p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">(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).</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">OR, is it something else?</span></p><p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal">
<span style="color:#1F497D">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.</span></p>
<p class="MsoNormal"><span style="color:#1F497D"> </span></p><p class="MsoNormal"><span style="color:#1F497D">Thanks,</span></p><p class="MsoNormal"><span style="color:#1F497D">~Sumit.</span></p><p class="MsoNormal"><span style="color:#1F497D">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?</span></p>
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