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Re: Decoupling of Network and Compute services for the new Network Service design


I think this is very much inline with what we've been thinking.  To me,
providing a clean and generic programming interface that decouples the
network functionality from the existing nova stack is a first step in
creating a standalone network service.

Also, I am not sure if this is implied by step #3 below, but it seems that
the compute and network service will need to share some identifier so that
the network entity running on the compute node can "recognize" a VM
interface and associate it with a vPort.  For example, each vNIC has an
identifier assigned by the compute service, a call to the network service
associates that vNIC id with a vPort, and when the compute node creates a
device (e.g., tap0), it tells the network plugin on the host the vNIC id for
that device (there are several other possible variations on this theme...).
 In your example below this may not be strictly required because all vNICs
get connected to the same network, but in a general model for a network
service this will be required.


On Wed, Feb 23, 2011 at 5:29 AM, Ishimoto, Ryu <ryu@xxxxxxxxxxx> wrote:

> Hi everyone,
> I have been following the discussion regarding the new 'pluggable' network
> service design, and wanted to drop in my 2 cents ;-)
> Looking at the current implementation of Nova, there seems to be a very
> strong coupling between compute and network services.  That is, tasks that
> are done by the network service are executed at the time of VM
> instantiation, making the compute code dependent on the network service, and
> vice versa.  This dependency seems undesirable to me as it adds restrictions
> to implementing 'pluggable' network services, which can vary, with many ways
> to implement them.
> Would anyone be opposed to completely separating out the network service
> logic from compute?  I don't think it's too difficult to accomplish this,
> but to do so, it will require that the network service tasks, such as IP
> allocation, be executed by the user prior to instantiating the VM.
> In the new network design(from what I've read up so far), there are
> concepts of vNICs, and vPorts, where vNICs are network interfaces that are
> associated with the VMs, and vPorts are logical ports that vNICs are plugged
> into for network connectivity.  If we are to decouple network and compute
> services, the steps required for FlatManager networking service would look
> something like:
> 1. Create ports for a network.  Each port is associated with an IP address
> in this particular case, since it's an IP-based network.
> 2. Create a vNIC
> 3. Plug a vNIC into an avaiable vPort.  In this case it just means mapping
> this vNIC to an unused IP address.
> 4. Start a VM with this vNIC.  vNIC is already mapped to an IP address, so
> compute does not have to ask the network service to do any IP allocation.
> In this simple example, by removing the request for IP allocation from
> compute, the network service is no longer needed during the VM
> instantiation.  While it may require more steps for the network setup in
> more complex cases, it would still hold true that, once the vNIC and vPort
> are mapped, compute service would not require any network service during the
> VM instantiation.
> IF there is still a need for the compute to access the network service,
> there is another way.  Currently, the setup of the network
> environment(bridge, vlan, etc) is all done by the compute service. With the
> new network model, these tasks should either be separated out into a
> standalone service('network agent') or at least be separated out into
> modules with generic APIs that the network plugin providers can implement.
>  By doing so, and if we can agree on a rule that the compute service must
> always go through the network agent to access the network service, we can
> still achieve the separation of compute from network services.   Network
> agents should have full access to the network service as they are both
> implemented by the same plugin provider.  Compute would not be aware of the
> network agent accessing the network service.
> With this design, the network service is only tied to the network REST API
> and the network agent, both of which are implemented by the plugin
> providers.  This would allow them to implement their network service without
> worrying about the details of the compute service.
> Please let me know if all this made any sense. :-)  Would love to get some
> feedbacks.
> Regards,
> Ryu Ishimoto
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Dan Wendlandt
Nicira Networks, Inc.
www.nicira.com | www.openvswitch.org
Sr. Product Manager
cell: 650-906-2650

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