[openstack-dev] [TripleO][Nova][Neutron] multiple hypervisors on one compute host - neutron agent and compute hostnames

Joe Gordon joe.gordon0 at gmail.com
Mon Aug 11 21:08:06 UTC 2014

On Tue, Aug 5, 2014 at 4:17 PM, Robert Collins <robertc at robertcollins.net>

> Hi!
> James has run into an issue implementing the multi-hypervisor spec
> (
> http://git.openstack.org/cgit/openstack/tripleo-specs/tree/specs/juno/tripleo-juno-deploy-cloud-hypervisor-type.rst
> )
> which we're hoping to use to reduce infrastructure overheads by
> deploying OpenStack control plane services in VMs, without requiring
> dedicated VM hypervisor machines in the deploy cloud.
> The issue we've hit is that the Neutron messages for VIF plugging are
> sent to the Neutron agent with an exactly matching hostname to the
> Nova-compute process. However, we have unique hostnames for the
> nova-compute processes on one machine (one for -kvm, one for -docker,
> one for -ironic etc) for a variety of reasons: so we can see if all
> the processes are up, so that we don't get messages for the wrong
> process from nova-api etc.

So you are running multiple nova-computes on a single node? This goes
against the model that nova is operating under. Instead of hacking a
workaround, if we think this is a use case nova/openstack should support,
why not have that discussion before deciding that the best solution is a
shallow patch.

> I think a reasonable step might be to allow the agent host option to
> be a list - e.g.
>  hosts={{nova.compute_hostname}}-libvirt,{{nova.compute_hostname}}-docker
> we'd just make it listen to all the nova-compute hostnames we may have
> on the machine.
> That seems like a fairly shallow patch to me: add a new hosts option
> with no default, change the code to listen to N queues when hosts is
> set, and to report state N times as well (for consistency).
> Alternatively, with a DB migration, we could record N hosts against
> one agent status.
> Alternatively we could run N ovs-agents on one machine (with a
> separate integration bridge each), but I worry that we'd encounter
> unexpected cross-chatter between them on things like external bridge
> flows.
> Thoughts?
> For now, we're going to have to run with a limitation of only one
> vif-plugging hypervisor type per machine - we'll make the agent
> hostname match that of the nova compute that needs VIFs plugged ;)
> -Rob
> --
> Robert Collins <rbtcollins at hp.com>
> Distinguished Technologist
> HP Converged Cloud
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> OpenStack-dev at lists.openstack.org
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