Re: [Engine-devel] API design and plan

----- Original Message ----- > 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.

Requiring an additional xml-rpc server sounds wrong to me.