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From Guillaume Nodet <gno...@gmail.com>
Subject Re: Some thoughts about enabling for OSGi
Date Tue, 25 Aug 2009 16:55:35 GMT
On Tue, Aug 25, 2009 at 17:43, Rick McGuire <rickmcg@gmail.com> wrote:

> I've been trying to pull together some thoughts about what it might mean
> for Geronimo to enable itself for OSGi applications and what needs to be
> added to the server beyond just adopting an OSGi classloading model.  That
> sort of change would be primarily transparent for most existing
> applications, but to make the change worthwhile, we'd also want to make
> Geronimo into a real OSGi application platform.
>
> So, beyond just having the framework environment, what would be the require
> elements?  Ok, to start with, most (all?) real OSGi platforms have some
> concept of a bundle repository.  The bundle repository is where installed
> bundles are stored and there is generally some sort of loading/provisioning
> strategy associated with the repository that eliminates the need for an
> application to manually install and start each of its dependent bundles.  I
> think the characteristics of how the Geronimo bundle repository is a
> discussion topic all of its own, so for now, I'll just assume this piece is
> there.  As part of server bootstrap, there will be a configured startup of
> bundles from the repository that are necessary to bring up the server.  This
> will be similar to the module bootstrapping the server already goes through.
>  There will also need to be a mechanism for adding bundles to the
> repository, probably both as a command line tool and via the console.
>
> The Geronimo server will need to provision the framework with an initial
> set of services that will be available for installed bundles to use.  Some
> of these services will interact with other portions of the Geronimo server,
> while others are platform-agnostic, but provide important bundle-management
> services.  Looking through the OSGi compendium specifications, the following
> look like a good recommended set:
>   * EventAdmin service (generalized Event broadcast service).  This is
>     fairly self contained, and we can probably just use the Felix
>     reference implementation.
>   * Logging service.  This is a standardized OSGi logging API.  The
>     reference implementation is just a circular queue and does not
>     actually log entries to any persistent storage.  The Geronimo OSGi
>     logging service should be integrated with the general logging
>     support.  The PAX logging service looks like a good starting point
>     for this.  I understand that the Geronimo Blueprint service
>     implementation is already using this version.
>   * Config Admin.  This is a persistent store for configuration data.     I
> think this one will be an general expectation for many bundles
>     that are installed on Geronimo, so we'd need to provide an
>     instance of this.


In addition, and related to Config Admin, support for meta type information
could be useful.  This allows describing what the configuration should look
like, and this allows automatic generation of UI for configuration for
example.  This is what the Felix web console does.


>
>   * UserAdmin service.  This is an interface to an authentication
>     system associated with a platform.  I believe this would be fairly
>     simple to map to the Geronimo authentication services.


I think there is a need for integrating the UserAdmin with JAAS at some
point.  I'm not aware of such a thing yet, but that's something I had in
mind.


>
>   * Declarative services.  The ability for bundles to declaratively
>     publish services to the services registry.  We'd need to support
>     this to allow bundles to be used portably across framework host
>     environments.  This should not require any special integration
>     with the rest of Geronimo.


Not sure if there is a need to support both by defaults.  If we rely on
Blueprint for example, DS could only be installed if users need that, as an
optional add-on maybe.


>
>   * Blueprint services.  A more sophisticated component assembly
>     model.  This also should not require any special Geronimo
>     integration.

* Preferences Service.  Allows bundles to persistently store
>     preference information.  This is a bundle-driven capability, which
>     is a bit different than the config admin service.  I'm not sure
>     how prevalently this is used, so this one might not be a requirement.
>
> Interestingly, this diagram of Karaf architecture has quite a bit in common
> with what I've just described once you replace "Spring DM" with "Blueprint
> Service".  There could be an advantage to leverage prior experience with
> this environment here.
>
> One key aspect to all of this is deployment and administration.  The
> Geronimo server will need to provide the conduit for deploying new bundles
> to this environment, as well as administrative function.  The OSGi
> Enterprise Expert Group (EEG) is working on a specification for using JMX
> for managing OSGi environments.  The reference implementation for this
> specification includes a framework neutral set of MBeans for tracking
> installed bundles, registered services, config admin, etc.  These look like
> a good model to follow and can be the basis for providing console-like
> administration capabilities.  There may be additional MBeans we'd like to
> provide for other services, such as the Blueprint service.
>
> This is probably a good staring point for the discussions.  There are
> likely other facilities we'll need to add here, but I think this is probably
> a good starting point for the discussions.
> Rick
>
>


-- 
Cheers,
Guillaume Nodet
------------------------
Blog: http://gnodet.blogspot.com/
------------------------
Open Source SOA
http://fusesource.com

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