On Mon, Apr 08, 2013 at 04:45:59PM -0700, David Lutterkort wrote:
On Mon, 2013-04-08 at 14:44 +0200, Jan Provaznik wrote:
There are some other downsides to using DC in process (as a library): it also significantly changes where DC can go architecturally. So far, the classic DC API has worked very hard to be stateless - CIMI isn't, and it wouldn't be unreasonable to introduce state into the classic DC API. That would be much more awkward if DC becomes a library.
I'm not familiar with DC plans (which sound really interesting) but even with stateful DC the lib could make sense:
- the DC lib - can be used by anyone who doesn't need any stateful feature
- DC/CIMI stateful service - built *on top* of the lib, wraps the lib
with REST API, adds stateful features
I think this is the right way to slice things up: make the DC service(s) wrappers around the DC library. The library essentially deals with adapting the internal driver API to something stable, and probably will make the API look a little more Rubyish. For example, right now code to start and stop an instance would look something like
dc = Deltacloud::new(some_backend, some_provider, credentials) inst = dc.create_instance(...) unless starts_automatically(dc) # needs to look at instance_states wait_for_state(dc, inst, "STOPPED") dc.start_instance(credentials, inst.id) end wait_for_state(dc, inst, "STARTED") .. do stuff with your running instance .. dc.stop_instance(dc, inst)
As you can see, the above isn't very Rubyish; it would be nicer to write
dc = Deltacloud::new(some_backend, some_provider, credentials) inst = dc.create_instance(...) if inst.initial_state == 'STOPPED' inst.poll_for { |inst| inst.stopped? } inst.start end inst.poll_for { |inst| inst.started? } .. do stuff with your running instance .. inst.stop
What I am mostly after is a feel for who's going to do the following around a DC library:
* Come up with a library API that is safe to use - that includes keeping the API stable and making sure we only expose reasonable parts of the driver API. We don't want an automatic "It's in the drivers, therefore it's part of the API" * Write enough tests to convince us that the library API still works * Document that API
Ok .. who's raising their hand ? ;)
David
I'd be pleased to work on that given I get permission from my manager to put some fraction of my time to this. I see this as a quite well defined, framed task that can be considered a "have a rest after the lunch" project.
It is surely highly relevant to both the Tracker (wherever it lands), the Broker and also Winged Monkey colleagues would be happy to see this and use it in their project I would hope.
Having this could bring more contributors to DC once the Ruby community sees the potential of DC compared to Fog.