[Engine-devel] Proposed next-generation vdsm API

[Itamar Heim]

> -----Original Message-----
> From: Adam Litke [mailto:agl at us.ibm.com]
> Sent: Thursday, December 01, 2011 0:41 AM
> To: vdsm-devel at lists.fedorahosted.org; engine-devel at 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?