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It is perhaps worth mentioning that there is an effort to implement a
generic synchronization mechanism (between Neutron and backend
controllers/devices) in the ML2 plugin [1]. A possible framework for its
eventual implementation is in an early discussion/proof-of-concept WIP
state [2].

-Mohammad

[1] https://blueprints.launchpad.net/neutron/+spec/ml2-driver-sync
[2] https://review.openstack.org/#/c/154333/



From:	Cory Benfield <Cory.Benfield at metaswitch.com>
To:	"OpenStack Development Mailing List (not for usage questions)"
            <openstack-dev at lists.openstack.org>
Date:	03/16/2015 04:48 AM
Subject:	Re: [openstack-dev] [neutron] Generic question about
            synchronizing	neutron agent on compute node with DB



On Sun, Mar 15, 2015 at 22:37:59, Sławek Kapłoński wrote:
> Maybe good idea for the beginning could be to implement some periodic
> task
> called from agent to check db config and compare it with real state on
> host?
> What do You think? Or maybe I'm competly wrong with such idea and it
> should be
> done in different way?

This is almost exactly what we do in our Calico ML2 driver. Each of our
agents will periodically request its complete state from a neutron-server
node and will ensure that its local state matches that expected state. This
interval is configurable, to allow administrators to make a trade-off
between DB/network load and convergence time.

With reliable transport this is in principle almost never needed (messages
only really get lost on agent crash, and the agent will resynchronize when
it starts back up anyway), but it provides assurances that the fabric is
capable of bringing itself into consistency without administrator
intervention.

Having similar function in other neutron agents would be valuable for the
exact same reasons, but do bear in mind the potentially increased load this
kind of resynchronization can place on databases and servers.

Cory
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