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From Mohammad Nour El-Din <>
Subject RE: [DISCUSS] OSGi framework for plugins and more?
Date Tue, 13 Nov 2012 07:30:47 GMT

   we already had this discussion before earlier when ACS was just donated
to ASF.

I am not an OSGi expert at all :), but I would like to know what is the
problem that needs to be solved rather than discussing the solution first

OSGi has a lot of magnificent features idd but do we really need them all,
and also what does all these features add to us in the context of the
context of the cloud. to be honest I don have a definite answer and that's
why I would suggest to list what we need to achieve regarding that part and
look into the alternatives and choose what is best for us, OSGi is one of
them for sure

Feedback/input ?

Sent from my Samsung Galaxy S3
Apologies for any typos
On Nov 13, 2012 7:56 AM, "Hugo Trippaers" <>
> > -----Original Message-----
> > From: Kelven Yang []
> > Sent: Monday, November 12, 2012 11:31 PM
> > To:
> > Subject: Re: [DISCUSS] OSGi framework for plugins and more?
> >
> >
> >
> > On 11/12/12 1:34 PM, "Chip Childers" <> wrote:
> >
> > >On Mon, Nov 12, 2012 at 4:12 AM, Hugo Trippaers
> > ><> wrote:
> > >> Hey  all,
> > >>
> > >> With the recent discussions on refactoring CloudStack and the working
> > >>going into javelin I would like to discuss using OSGi. The background
> > >>is that I have been struggling with ideas on how to setup a plugin
> > >>system for CloudStack that would allow plugins to be separate entities
> > >>which can be release independently from CloudStack core. Mainly to
> > >>deal with the current non-asf components but for future expansion as
> > well.
> > >>
> > >> While at ApacheConEU I had the chance to discuss these ideas with one
> > >>of our mentors after his talk about OSGi. I'm pretty charmed by OSGi
> > >>and the options it provides. It's a well thought out system that allow
> > >>true modularity and pluggability. With the amount of support in the
> > >>java industry it's a standard that feels very mature and a safe bet,
> > >>one I would prefer to any homegrown plugin system. It supports
> > >>versioning of components, strict separation of classes between
> > >>components and all kind of funky features like hot-plugging and
> > >>hot-replace. Using OSGi would mean that people can supply bundles with
> > >>functionality which are maintained separately from the 'main code'
> > >>without having to worry about how to integrate it with the core. Just
> > >>putting the module in the right directory should be enough to get
> > CloudStack to see and use the bundle.
> > >>Upgrades happen the same way, new version of an authenticator, just
> > >>replace the bundle and let the framework replace it with having to
> > >>shutdown the server at all.
> > >>
> > >> As we are discussing making CloudStack more modular, I would like to
> > >>propose to start using OSGi for this. It is a bit of a learning curve
> > >>to start with, but one we can get help with from our mentors. I'm
> > >>already working on setting up a proof of concept for a plugin system
> > >>using OSGi together with a colleague to show how it works, code is
> > >>always better than words.
> > >>
> > >> So what are your thoughts?
> > >>
> > >> Cheers,
> > >>
> > >> Hugo
> > >>
> > >
> > >I'm not familiar enough with OSGi to understand the tradeoffs of that
> > >vs other frameworks, but I'd suggest that Kelvin weigh in here.  The
> > >work that he's doing on the Javelin branch is similar, and there might
> > >be an argument for Spring instead.
> > >
> > >Kelvin, I know you just responded on the other thread about the
> > >relative timing of a switch.  Want to weigh in on the OSGi approach's
> > >technical merit vs. other options?
> >
> > It will be nice to see the OSGi technical merit vs. other option in
> > Laying out these basic but fundamental frames may not benefit a lot in
> > short term, but we may get fully paid in long term. Spring can only
give us
> > solution on compile-time/load-time component integration, it focuses
> > more on internal component wiring, OSGi seems to focus more at runtime,
> > think these two may be complementary to each other.
> To a certain extent these technologies can be used together, but not in
this way it seems. OSGi is a framework that focusses on separation of code
in various modules in such a way that other modules can not see and work
with the classes in other modules excluding via well defined services. This
is a fundamental choice that touches the core of how CloudStack would be
put together. Instead of a single codebase (or at runtime a single
classloader) where modules would be loaded via (for example) the spring
framework based on an xml definition, the core would be an empty framework
and modules work be plugged in and provide a certain service. This can be
done at load time or runtime, that up to the implementers. For example say
the core module would need a vm provisioned it would ask the service
registry if there was a service able to provide this functionality, if
there was that service would be asked to perform that task. Here is a short
post that describes the context far better than I can: real benefits are in also in the modularity,
because the framework is
very strict on what bundles/interfaces are exposed and required, using the
proper interfaces and limiting yourself to exposed interfaces is enforced
by the framework.
> Hugo
> >
> >
> > >
> > >-chip

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