On Thu, Dec 08, 2011 at 04:56:17AM -0500, Ayal Baron wrote:
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On Tue, Dec 06, 2011 at 08:46:57AM -0600, Adam Litke wrote:
On Tue, Dec 06, 2011 at 02:58:59PM +0200, Dan Kenigsberg wrote:
On Mon, Dec 05, 2011 at 11:34:18AM -0600, Adam Litke wrote:
Hi everyone. On today's VDSM call we discussed the requirements, design, and plan for updating the API to include support for QMF and single-host REST API. All members present arrived at a general consensus on the best way to design the next-generation API. I have tried to capture this discussion in the oVirt wiki:
http://ovirt.org/wiki/Vdsm_API
Please take a look at this page and let's discuss any changes that may be needed in order to adopt it as a working plan that we can begin to execute. Thanks!
Very nice, I've fixed two bullets about the future of the xml-rpc.
Thanks... Updates look good to me.
I think that we are missing something here: how do we model Vdsm-to-Vdsm communication, in a binding-blind way? I'm less worried about the storage-based mailbox used for lvextend requests: my problem is with migration command.
Ok, interesting... Besides migration, are there other features (current or planned) that would involve P2P communication? I want to ensure we consider the full problem space.
Well, I can imagine we would like a host in distress to migrate VMs to whomever can take them, without central management driving this process. (CAVE split brain)
At the momemt I cannot think of something that cannot be implemented by QMF events. Ayal?
Currently, the implementation of the "migrate" verb includes contacting the remote Vdsm over xml-rpc before issuing the libvirt migrateToURI2 command ('migrationCreate' verb).
A Vdsm user who choose to use the REST binding, is likely to want this to be implemented this using a REST request to the destination. This means that the implementation of Vdsm depends on the chosen binding.
The issue can be mitigating by requiring the binding level to provide a "callback" for migrationCreate (and any other future Vdsm->world requests). This would complicate the beautiful png at http://ovirt.org/wiki/Vdsm_API#Design ... Does anyone have another suggestion?
Actually, I think you are blending the external API with vdsm internals. As a management server or ovirt-engine, I don't care about the protocol that vdsm uses to contact the migration recipient. As far as I am concerned this is a special case internal function call. For that purpose, I think xmlrpc is perfectly well-suited to the task and should be used unconditionally, regardless of the bindings used to initiate the migration.
So I would propose that we modify the design such that we keep an extremely thin xmlrpc server active whose sole purpose is to service internal P2P requests.
Interesting. We could avoid even that, if we could register a callback with libvirt, so that destination libvirtd called destination Vdsm to verify that all storage and networking resources are ready, before executing qemu. DanPB, can something like that be done? (I guess it is not realistic since we may need to pass vdsm-specific data from source to dest, and libvirt is not supposed to be a general purpose transport.)
Dan.
I don't understand the issue. The whole point of the REST API is to be an easily consumable *single* node management API. Once you start coordinating among different nodes then you need clustering and management (either distributed or centralized), in both cases it is fine to require having a bus in which case you have your method of communications between hosts to replace current xml-rpc.
Implicit in this statement is an assertion that live migration between two vdsm instances will not be supported without orchestration from an ovirt-engine instance. I don't agree with placing such a limitation on vdsm since p2p migration is already well-supported by the underlying components (libvirt and qemu).
Requiring an additional xml-rpc server sounds wrong to me.
The other option is to support a migrateCreate binding in REST and QMF. -- Adam Litke <agl@us.ibm.com> IBM Linux Technology Center