[openstack-dev] [Quantum] notifications vs specific RPC calls between agents

Dan Wendlandt dan at nicira.com
Thu Aug 9 21:25:29 UTC 2012


On Thu, Aug 9, 2012 at 1:13 PM, Mark McClain <mark.mcclain at dreamhost.com>wrote:

> All-
>
> I wanted to widen the discussion that we've been having on
> https://review.openstack.org/#/c/10997/
>
> Basically the DHCP Agent needs to be notified about certain Quantum
> events.  There are two ways of accomplishing this:
>
> 1) Turn on Quantum notifications and have the agent consume the general
> notifications.  Moving forward this would require that rabbit_notifications
> always be enabled in quantum.conf.
>
> Pro: This functionality already exists in Quantum.
> Con: These messages are more general, so the agent typically has to
> collect some data in response to the calls.
>

This is my preference, as I think it leads to a cleaner design and avoid a
bunch of specific notifications within Quantum.  I'd really like something
like DHCP to be implemented in a way that is basically agnostic to the
plugin that is running (i.e., consuming standard notifications, and
interacting via the main Quantum API).   This let's people build additional
such services (e.g., integrating quantum IPAM with DNS) without modifying
the core code.

We actually had a substantial thread on this topic a few weeks ago in the
context of plugin-agents, and the concern was that there currently wasn't a
channel other than RPC to pass some information (e.g., the VLAN a network
maps to), so we said that for F-3 plugins could create their own RPC
mechanisms if needed.  That said, I'd still like to see things more toward
a model where we use "standard" notifications.

Dan




>
> Note: The rabbit_notifier actually works will all of the messaging
> backends, i.e. qpid.)  These messages are more general in nature and just
> provide the data returned from the plugin.
>
> 2) Create specific RPC calls that q-svc fans out to the DHCP agent(s).
>
> Pro: This approach means that the Quantum server can send messages that
> are specifically tailored for the DHCP agent to act upon.
> Con: Essentially implements a subset of the notification API in a specific
> way.
>
> I'm open to either approach, but would like the community's input.
> Thoughts?
>
> mark
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>



-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Dan Wendlandt
Nicira, Inc: www.nicira.com
twitter: danwendlandt
~~~~~~~~~~~~~~~~~~~~~~~~~~~
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