On 04/26/2012 09:24 AM, Sumit Naiksatam (snaiksat) wrote:
Hi Gary,
Thanks for taking up the work on improving the HA aspects of some of
the agents. (I will respond to your review request once I get a chance
to test the changes, but the diff looks good.)
Thanks
I agree with your assessment that the factoring of common agent code
is probably a larger activity, and probably can be targeted as a
separate patch.
On your question regarding the need for an agent and if it can be done
in the VIF driver -- the VIF driver is not actually an independent
thread of control, it gets executed as a part of the VM creation
process. If a VM's VIF had to be always plugged into the corresponding
port only when a VM was created, then I guess it would be fine to do
the plugging from with the VIF driver. However, we also want to be
able to support the use case that you can bring up the VM and then
plug it into a port at a later time, or unplug and plug into a
different network.
Thanks for the clarification. This makes sense :)
In general, there is also a thought that the VIF driver should be
really thin, and to the extent possible Quantum plugin-specific
details should be pulled out it.
Thanks,
~Sumit.
*From:*netstack-bounces+snaiksat=cisco....@lists.launchpad.net
[mailto:netstack-bounces+snaiksat=cisco....@lists.launchpad.net] *On
Behalf Of *Gary Kotton
*Sent:* Wednesday, April 25, 2012 12:55 AM
*To:* netstack@lists.launchpad.net
*Subject:* [Netstack] Quantum agents
Hi,
Sorry for not being able to attend the IRC meeting - it was in the
middle of the night :)
Whilst I was working on the integration of Quantum into oVirt I
encountered a number of issues and challenges regarding the agents.
Some of the issues were discussed in yesterdays meeting namely:
1. High availability
2. Scalability
*High Availability*
I discovered that when the agent was unable to access the database it
would terminate on a exception. This has been addressed partially by
https://review.openstack.org/#/c/6744/ (thanks to Maru Newby for the
comments - updated, tested manullay for linuxbridge and ovs). I saw
that Maru opened a bug regarding agent unit tests (kudos). I have
tested the ovs agent and the linux bridge agent manually.
I have yet to update the RYU agent (Isaku Yamahata suggested that we
speak about this at the meeting). I think that we need to address this
across the board and not only in the agents, but also in the plugins.
The database access should be done via a common class that takes the
connectivity into account. I do not feel that this is part of the bug
fix above it is more of a system wide fix.
*Scalability*
This is a recurring topic. I understand that from the summit the idea
of using AMQP came up. This still requires a "PUSH" from the plugin to
the specific agent. After dealing with the agents above I wonder if we
actually need the agents? Let me try and elaborate: when a VM is
deployed the VIF plugin (I think that that is the terminology) creates
the tap device, sets it to up and in the case of OVS notifies the
integration bridge of the tap device. In the background the agent is
running. When the agent discovers that the tap device exists and it
matches a attachment from the database it "plugs" the device in and
updates the database with the port status.
Why not have the VIF plugin also do the interface plugin? This can and
may solve a large number of scalability issues mentioned. This will be
moving part of the logic from the agent to the VIF plugin.
It would be intersting to know the rationale of the current
implementation.
Thanks
Gary
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