On 06/19/2012 01:13 AM, Ryan Harper wrote:
* Saggi Mizrahi<smizr...@redhat.com>  [2012-06-18 10:05]:
I would like to put on to the table for descussion the 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.


Thanks for sending this out.  I've been trying to pull together some
thoughts on what else is needed for vdsm as a community.  I know that
for some time downstream has been the driving force for all of the work
and now with a community there are challenges in finding our own way.

While we certainly don't want to make downstream efforts harder, I think
we need to develop and support our own vision for what vdsm can be come,
some what independent of downstream and other exploiters.

Revisiting the API is definitely a much needed endeavor and I think
adding some use-cases or sample applications would be useful in
demonstrating whether or not we're evolving the API into something
easier to use for applications beyond engine.

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
I agree with the list, but I'd like to work on the redesign discussion so
that we're not doing all of 1-4 around the existing API that's

I'm over due for posting a feature page on vdsm standalone mode, and I
have some other thoughts on various uses.

Some other paths of thought for use-cases I've been mulling over:

     - Simplifying using QEMU/KVM
         - consuming qemu via command line
             - can we manage/support developers launching qemu directly
         - consuming qemu via libvirt
             - can we integrate with systems that are already using

     - Addressing issues with libvirt
         - are there kvm specific features we can exploit that libvirt

     - Scale-up/fail-over
         - can we support a single vdsm node, but allow for building up
         clusters/groups without bringing in something like ovirt-engine
         - can we look at decentralized fail-over for reliability without
         a central mgmt server?

     - pluggability
         - can we support an API that allows for third-party plugins to
         support new features or changes in implementation?

Pluggability feature would be nice. Even nicer would be the ability to introspect and figure whats supported by VDSM. For eg: It would be nice to query what plugins/capabilities are supported and accordingly the client can take a decision and/or call the appropriate APIs w/o worrying about ENOTSUPP kind of error. It does becomes blur when we talk about Repository Engines... that was also targetted to provide pluggaibility in managing Images.. how will that co-exist with API level pluggability ?

IIUC, StorageProvisioning (via libstoragemgmt) can be one such optional support that can fit as a plug-in nicely, right ?

     - kvm tool integration into the API
         - there are lots of different kvm virt tools for various tasks
         and they are all stand-alone tools.  Can we integrate their
         use into the node level API.  Think libguestfs, virt-install,
         p2v/v2v tooling.  All of these are available, but there isn't an
         easy way to use this tools through an API.

     - host management operations
         - vdsm already does some host level configuration (see
               networking e.g.) it would be good to think about extending
         the API to cover other areas of configuration and updates
             - hardware enumeration
             - driver level information
             - storage configuration
                 (we've got a bit of a discussion going around
                  libstoragemgmt here)

     - performance monitoring/debugging
         - is the host collecting enough information to do debug/perf
         - can we support specific configurations of a host that optimize
         for specific workloads
             - and can we do this in the API such that third-parties can
             supply and maintain specific workload configurations

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.

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