[openstack-dev] Unified Guest Agent proposal

Dmitry Mescheryakov dmescheryakov at mirantis.com
Fri Dec 13 22:06:33 UTC 2013

2013/12/13 Alessandro Pilotti <apilotti at cloudbasesolutions.com>

> Hi guys,
> This seems to become a pretty long thread with quite a lot of ideas. What
> do you think about setting up a meeting on IRC to talk about what direction
> to take?
> IMO this has the potential of becoming a completely separated project to
> be hosted on stackforge or similar.
> Generally speaking, we already use Cloudbase-Init, which beside being the
> de facto standard Windows "Cloud-Init type feature” (Apache 2 licensed)
> has been recently used as a base to provide the same functionality on
> FreeBSD.
> For reference: https://github.com/cloudbase/cloudbase-init and
> http://www.cloudbase.it/cloud-init-for-windows-instances/
> We’re seriously thinking if we should transform Cloudbase-init into an
> agent or if we should keep it on line with the current “init only, let the
> guest to the rest” approach which fits pretty
> well with the most common deployment approaches (Heat, Puppet / Chef,
> Salt, etc). Last time I spoke with Scott about this agent stuff for
> cloud-init, the general intention was
> to keep the init approach as well (please correct me if I missed something
> in the meantime).
> The limitations that we see, independently from which direction and tool
> will be adopted for the agent, are mainly in the metadata services and the
> way OpenStack users employ them to
> communicate with Nova, Heat and the rest of the pack as orchestration
> requirements complexity increases:
> 1) We need a way to post back small amounts of data (e.g. like we already
> do for the encrypted Windows password) for status updates,
> so that the users know how things are going and can be properly notified
> in case of post-boot errors. This might be irrelevant as long as you just
> create a user and deploy some SSH keys,
> but becomes very important for most orchestration templates.
> 2) The HTTP metadata service accessible from the guest with its magic
> number is IMO quite far from an optimal solution. Since every hypervisor
> commonly
> used in OpenStack (e.g. KVM, XenServer, Hyper-V, ESXi) provides guest /
> host communication services, we could define a common abstraction layer
> which will
> include a guest side (to be included in cloud-init, cloudbase-init, etc)
> and a hypervisor side, to be implemented for each hypervisor and included
> in the related Nova drivers.
> This has already been proposed / implemented in various third party
> scenarios, but never under the OpenStack umbrella for multiple hypervisors.
> Metadata info can be at that point retrieved and posted by the Nova driver
> in a secure way and proxied to / from the guest whithout needing to expose
> the metadata
> service to the guest itself. This would also simplify Neutron, as we could
> get rid of the complexity of the Neutron metadata proxy.
The idea was discussed in the thread with name 'hypervisor-dependent
agent'. A couple existing agents were proposed: Rackspace agent for Xen
[1][2] and oVirt agent for Qemu [3].

Many people prefer the idea of hypervisor independent agent which will
communicate over network (network agent). The main disadvantage of
hypervisor-dependent agent is obviously the number of implementations need
to be made for different hypervisors/OSes. Also it needs a daemon (in fact
- another agent) running on each Compute host.

IMHO these are very strong arguments for network-based agent. If we start
with hypervisor-dependent agent, it will just take too much time to do
enough implementations. On the other hand, these two types of agents can
share some code. So if need arise, people can write hypervisor-dependent
agent based on network one, or behaving the same way. AFAIK, that is how
Trove is deployed in Rackspace. Trove has network-based agent, and
Rackspace replaces it with their own implementation.

[1] https://github.com/rackerlabs/openstack-guest-agents-unix
[2] https://github.com/rackerlabs/openstack-guest-agents-windows-xenserver
[3] https://github.com/oVirt/ovirt-guest-agent

> Alessandro
> On 13 Dec 2013, at 16:28 , Scott Moser <smoser at ubuntu.com> wrote:
> > On Tue, 10 Dec 2013, Ian Wells wrote:
> >
> >> On 10 December 2013 20:55, Clint Byrum <clint at fewbar.com> wrote:
> >>
> >>> If it is just a network API, it works the same for everybody. This
> >>> makes it simpler, and thus easier to scale out independently of compute
> >>> hosts. It is also something we already support and can very easily
> expand
> >>> by just adding a tiny bit of functionality to neutron-metadata-agent.
> >>>
> >>> In fact we can even push routes via DHCP to send agent traffic through
> >>> a different neutron-metadata-agent, so I don't see any issue where we
> >>> are piling anything on top of an overstressed single resource. We can
> >>> have neutron route this traffic directly to the Heat API which hosts
> it,
> >>> and that can be load balanced and etc. etc. What is the exact scenario
> >>> you're trying to avoid?
> >>>
> >>
> >> You may be making even this harder than it needs to be.  You can create
> >> multiple networks and attach machines to multiple networks.  Every
> point so
> >> far has been 'why don't we use <idea> as a backdoor into our VM without
> >> affecting the VM in any other way' - why can't that just be one more
> >> network interface set aside for whatever management  instructions are
> >> appropriate?  And then what needs pushing into Neutron is nothing more
> >> complex than strong port firewalling to prevent the slaves/minions
> talking
> >> to each other.  If you absolutely must make the communication come from
> a
> >
> > +1
> >
> > tcp/ip works *really* well as a communication mechanism.  I'm planning on
> > using it to send this email.
> >
> > For controlled guests, simply don't break your networking.  Anything that
> > could break networking can break /dev/<hypervisor-socket> also.
> >
> > Fwiw, we already have an extremely functional "agent" in just about every
> > [linux] node in sshd.  Its capable of marshalling just about anything in
> > and out of the node. (note, i fully realize there are good reasons for
> > more specific agent, lots of them exist).
> >
> > I've really never understood "we don't want to rely on networking as a
> > transport".
> >
> >> system agent and go to a VM, then that can be done by attaching the
> system
> >> agent to the administrative network - from within the system agent,
> which
> >> is the thing that needs this, rather than within Neutron, which doesn't
> >> really care how you use its networks.  I prefer solutions where other
> tools
> >> don't have to make you a special case.
> >
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