[Engine-devel] [virt-node] VDSM as a general purpose virt host manager

[Shu Ming]

On 2012-6-20 5:32, Saggi Mizrahi wrote:
> There is an important discussion starting about the future of the VDSM API on
> vdsm-devel. If you want to be involved in the future of the VDSM API don't miss
> out and join vdsm-devel. To sign up go to
> https://fedorahosted.org/mailman/listinfo/vdsm-devel
>
> There growing need for a way to more easily reuse of the functionality of VDSM
> in order to service projects other than Ovirt-Engine.
>
> Originally VDSM was created as a proprietary agent for the sole purpose of
> serving the then proprietary version of what is known as ovirt-engine. Red Hat,
> after acquiring the technology, pressed on with it's commitment to open source
> ideals and released the code. But just releasing code into the wild doesn't
> build a community or makes a project successful. Further more when building
> open source software you should aspire to build reusable components instead of
> monolithic stacks.
>
> We would like to expose a stable, documented, well supported API. This gives
> us a chance to rethink the VDSM API from the ground up. There is already work
> in progress of making the internal logic of VDSM separate enough from the API
> layer so we could continue feature development and bug fixing while designing
> the API of the future.
>
> In order to achieve this though we need to do several things:
>     1. Declare API supportability guidelines
>     2. Decide on an API transport (e.g. REST, ZMQ, AMQP)
>     3. Make the API easily consumable (e.g. proper docs, example code, extending
>        the API, etc)
>     4. Implement the API itself
Now,  VDSM version was highly bound with oVirt Engine version.  In order 
to make oVirt to work, both VDSM and ovirt engine should be synced with 
the latest binary, no back compatibility yet.  If we want to break this 
binding out,  we should classify the level of the VDSM APIs like these:

1) public stable
2) public evolving
3) undocumented volatile

And the we should make sure public stable interfaces to be supported in 
a very long time as possible as we can.  public evolving interfaces 
should keep the compatibility in the same major release(ie, 4.x.x). 
undocumented volatile is not recommended to the application and it is 
the responsibility of the application to take the risk.


>
> All of these are dependent on one another and the permutations are endless.
> This is why I think we should try and work on each one separately. All
> discussions will be done openly on the mailing list and until the final version
> comes out nothing is set in stone.
>
> If you think you have anything to contribute to this process, please do so
> either by commenting on the discussions or by sending code/docs/whatever
> patches. Once the API solidifies it will be quite difficult to change
> fundamental things, so speak now or forever hold your peace. Note that this is
> just an introductory email. There will be a quick follow up email to kick start
> the discussions. Don't forget to sign up to the vdsm-devel mailing list.
> _______________________________________________
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> Engine-devel at ovirt.org
> http://lists.ovirt.org/mailman/listinfo/engine-devel
>


-- 
Shu Ming <shuming at linux.vnet.ibm.com>
IBM China Systems and Technology Laboratory