8:02 a.m.
----- Original Message -----
> -----Original Message-----
> From: Adam Litke [mailto:agl@us.ibm.com]
> Sent: Thursday, December 01, 2011 0:41 AM
> To: vdsm-devel(a)lists.fedorahosted.org; engine-devel(a)ovirt.org
> Cc: Daniel P. Berrange; Chris Wright; Dan Kenigsberg; Itamar Heim
> Subject: Proposed next-generation vdsm API
>
> Recently we've had some very productive discussions concerning the
> VDSM
API. I
> want to attempt to refocus the discussion around an emerging
> proposal
and see if
> we can agree on a sensible path forward.
>
> Based on the discussion, I have identified the following
> requirements
that
> a new API for vdsm should have:
>
> 1.) Single API that can be consumed by ovirt-engine and ISVs
> - We don't want to maintain multiple parallel APIs
> - To develop a vendor ecosystem, we must have a robust external
> API to
> vdsm
>
> 2.) Full vdsm capabilities are exposed without requiring
> ovirt-engine
> - ovirt components should be modular and independently useful
> - Some deployments might want to manage nodes without ovirt-engine
>
> 3.) Standardized protocol with low overhead
> - Required for widespread adoption
>
> 4.) Support for asynchronous tasks and events
> - Needed by ovirt-engine and other consumers
>
> Based on these requirements, the following proposal has started to
emerge:
>
> Create a REST API that will provide all of the functionality that
> is
currently
> available via the xmlrpc interface (with the goal of deprecating
> xmlrpc
once it
> becomes mature enough). To support advanced clustering features
> that
> ovirt-engine is planning, we'll write an QMF broker that can proxy
> the
REST API
> onto a message bus. ovirt-engine will interact with vdsm
> exclusively
over this
> bus but the REST API will be the principle API and the entry point
> for
ISV apps.
> A REST API provides a light-weight and standard way to access all
> of the
vdsm
> functionality.
>
> The REST API will handle events by exposing a new 'events'
> collection at
the api
> root. REST users will use some sort of polling to collect these
> events.
The
> details of this interface are being worked on. Several ways for
minimizing the
> impact of polling have been discussed. The QMF broker can expose a
> publish/subscribe model for events as appropriate.
>
> Is this model an acceptable way to improve the vdsm API? I would
> like
to hear
> the opinions of ovirt-engine developers, vdsm developers, and other
> stakeholders. Thanks for providing feedback on this proposal!
Why things non native to REST and wrap it in QMF, rather than do the
reverse?
Or just to them in parallel, since it sounds like both are going to
be
first class citizens?
This was more my understanding from our discussion on IRC yesterday.
REST API - everything that is relevant for single node management
QMF - same API as above + multi-node relevant API calls. I don't see any reason for
doing weird things over REST to support the latter.
In fact, I don't even see any real reason for going through the REST API when using
QMF.
If you take a look at today's API you will see that there is nothing there that limits
it to XML-RPC and we could easily expose all the calls using REST or anything else.
In python, exposing a new verb in the various APIs can be automatic so this would require
very little maintenance. Any multi-node or transport specific calls can be decorated as
such and would be automatically ignored/picked up by the relevant API layer.
This way, we could also easily enable using different bus protocols assuming a customer
already has a deployment as was suggested yesterday.
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