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