[openstack-dev] Unified Guest Agent proposal

Dmitry Mescheryakov dmescheryakov at mirantis.com
Fri Dec 13 20:24:40 UTC 2013

2013/12/13 Fox, Kevin M <kevin.fox at pnnl.gov>

> Yeah, I think the extra nic is unnecessary too. There already is a working
> route to, and a metadata proxy -> server running on it.
> So... lets brainstorm for a minute and see if there are enough pieces
> already to do most of the work.
> We already have:
>   * An http channel out from private vm's, past network namespaces all the
> way to the node running the neutron-metadata-agent.
> We need:
>   * Some way to send a command, plus arguments to the vm to execute some
> action and get a response back.
> OpenStack has focused on REST api's for most things and I think that is a
> great tradition to continue. This allows the custom agent plugins to be
> written in any language that can speak http (All of them?) on any platform.
> A REST api running in the vm wouldn't be accessible from the outside
> though on a private network.
> Random thought, can some glue "unified guest agent" be written to bridge
> the gap?
> How about something like the following:
> The "unified guest agent" starts up, makes an http request to
> If at any time the connection returns, it will auto reconnect.
> It will block as long as possible and the data returned will be an http
> request. The request will have a special header with a request id.
> The http request will be forwarded to localhost:<someportfromconfigfile>
> and the response will be posted to
> The neutron-proxy-server would need to be modified slightly so that, if it
> sees a /unified-agent/<cnc_type>/* request it:
> looks in its config file, unified-agent section, and finds the ip/port to
> contact for a given <cnc_type>', and forwards the request to that server,
> instead of the regular metadata one.
> Once this is in place, savana or trove can have their webapi registered
> with the proxy as the server for the "savana" or "trove" cnc_type. They
> will be contacted by the clients as they come up, and will be able to make
> web requests to them, an get responses back.
> What do you think?
> Thanks,
> Kevin

Kevin, frankly that sound like a _big_ overkill and wheel re-invention. The
idea you propose is similar to HTTP long polling. It actually works in the
browsers. But I think people use it not because it is very scalable,
easy-implemented or something else. It is simply one of the few
technologies available when you need to implement server push in the web.

In our use-case we don't have a limitation 'that must work with a bare
browser on client side' and hence we can use technologies which much better
suite to message passing like AMQP, STOMP or others.

> ________________________________________
> From: Ian Wells [ijw.ubuntu at cack.org.uk]
> Sent: Thursday, December 12, 2013 11:02 AM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] Unified Guest Agent proposal
> On 12 December 2013 19:48, Clint Byrum <clint at fewbar.com<mailto:
> clint at fewbar.com>> wrote:
> Excerpts from Jay Pipes's message of 2013-12-12 10:15:13 -0800:
> > On 12/10/2013 03:49 PM, Ian Wells wrote:
> > > On 10 December 2013 20:55, Clint Byrum <clint at fewbar.com<mailto:
> clint at fewbar.com>
> > > <mailto:clint at fewbar.com<mailto:clint at fewbar.com>>> wrote:
> > I've read through this email thread with quite a bit of curiosity, and I
> > have to say what Ian says above makes a lot of sense to me. If Neutron
> > can handle the creation of a "management vNIC" that has some associated
> > iptables rules governing it that provides a level of security for guest
> > <-> host and guest <-> $OpenStackService, then the transport problem
> > domain is essentially solved, and Neutron can be happily ignorant (as it
> > should be) of any guest agent communication with anything else.
> >
> Indeed I think it could work, however I think the NIC is unnecessary.
> Seems likely even with a second NIC that said address will be something
> like (or the ipv6 equivalent?).
> There *is* no ipv6 equivalent, which is one standing problem.  Another is
> that (and admittedly you can quibble about this problem's significance) you
> need a router on a network to be able to get to - I raise
> that because the obvious use case for multiple networks is to have a net
> which is *not* attached to the outside world so that you can layer e.g. a
> private DB service behind your app servers.
> Neither of these are criticisms of your suggestion as much as they are
> standing issues with the current architecture.
> --
> Ian.
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