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From Jean-Sebastien Delfino <jsdelf...@apache.org>
Subject Re: Geronimo/Tuscany integration
Date Tue, 26 Jun 2007 21:33:26 GMT
Raymond is away for one more week, so I'll try to answer some of these 
questions.


Manu George wrote:
> Hi Raymond/Jay,
>
>      I would like to join this effort. I would like to discuss what
> is expected of the deep integration. I will just list down my
> understanding of both the current and proposed integrations
>
> Understanding of the Current Integration
>
> 1) TuscanyContextListener creates an SCA domain when the servlet is
> created and then destroys it when the servlet is destroyed.
> 2) During SCA domain creation it looks up the composites and deploys
> them in the domain
> Creates a webapp module activator for registering servlet hosts.
> 3) Finally we have a servlet that forwards requests to the servlet
> registered with the Tuscany Servlet Host.
> 4) An SCADomain is created for each application and we can lookup the
> services from the SCADomain.
> 5) During SCADomain creation a runtime is also created for the 
> DefaultSCADomain.
> 7) All tuscany classes are loaded repeatedly for each application in
> separate classloaders.
> 8) A runtime is created per application

Correct. I'm assuming that you're talking about the current Webapp 
integration.

As a heads up the SCADomain class is probably going to change a bit to 
load a subset of components deployed to an actual SCA domain. The idea 
is to distribute an SCA domain across runtimes, each runtime running one 
or more domain level SCA components (and components nested in their 
composites).

>
> Understanding/Doubts about the proposed Integration.
>
> 1) Each SCA application will have an SCA module which will be a jar
> with an SCDL in META-INF. This jar can also be part of an EAR. . There
> will be a Tuscany deployer that will take care of deploying the SCA
> modules. Should WAR files be also able to contain SCA jars?

Will the application developer be exposed to this? If it's the case then 
it looks like a new programming / packaging  model, different from SCA :)

An SCA application developer normally packages application artifacts in 
an SCA contribution (a form of archive described in the SCA assembly 
spec) and the .composite (SCDL) files are not necessarily under 
META-INF. in fact usually we place them with the other development 
artifacts, .Java, .wsdl, .groovy etc. I was hoping that the application 
developer wouldn't have to learn a different packaging model to run his 
SCA components on Geronimo. Will there be a way to deploy an SCA 
contribution to Geronimo "natively" without having to repackage it in a 
J2EE archive?
 
> 2) Each App will have an SCA Domain which will be instantiated when
> the application starts. Is this assumption correct or can there be
> multiple SCADomains per app?

The objects deployed to an SCA domain and which run on an SCA runtime 
are SCA components. There is no concept of an App like a J2EE App in SCA 
at the moment.

Components can be implemented by a simple Java class, a BPEL process, a 
script, etc. or a Composite. A Composite describes an assembly of 
Components, allowing for nested composition of components. An SCA domain 
is described by a composite, describing the assembly of top level 
components in an administration domain. The SCA domain composite does 
not necessarily have to written to a single .composite file since it has 
to be distributed, but it is effectively modeled as a composite.

So to go back to your question, objects that run on an SCA runtime are 
SCA components, and each component belongs to a single SCA Domain composite.

Now with respect to instances of the SCADomain class, I was thinking 
about two options:

(a) one instance of SCADomain per component running on the server, 
loaded with a subset of the distributed SCA domain composite 
representing that component and enough information about its peer 
components for it to locate and wire to them.

(b) a single SCADomain object per Geronimo server, loaded with all the 
components running on the server. This will save a little bit of memory, 
at the expense of more synchronization work.

I'd suggest to start with option (a) as it's the model that needs to be 
supported when SCA components run on different physical machines as 
well, and I'm actually not sure that we'll get any real performance gain 
with (b) over (a) if we do (a) right.

> 3) The Tuscany classes are loaded only once and then shared between
> the different SCA applications.

+1

> 4) There will be multiple domains instantiated from different
> applications and there should be a server wide domain registry where
> applications can look up and invoke different composites from domains
> different from their own. (Can this be Global JNDI/Gbean refs or is
> there something specific in tuscany).

An SCA domain is a domain of administration typically containing 
multiple servers. Wiring and lookups are assumed to work within the 
context of a single domain. We could imagine a Geronimo server hosting 
components from multiple SCA administration domains, but I'm not sure 
that it's going to be a very common scenario.

> 5) There should be only a single Tuscany Runtime for the entire
> geronimo instance.

It if helps, sure. If on the other hand it complicates things we can 
also have multiple runtime instances. Multiple lightweight runtime 
instances may be easier to handle than a single more complicated one.

> 6) How can we lookup the services running in one geronimo instance
> from an app in another geronimo instance. Is this supported in Tuscany
>

This looks like the distributed domain deployment that we need to 
support in Tuscany in general. Two runtimes R1 and R2, running on two 
different machines, access the SCA composite model describing an SCA 
domain. Runtime R1 runs component CA, runtime R2 runs component CB. CA 
has an SCA reference wired to CB.

We are starting to work on this in Tuscany, along the lines of what I've 
described above in my answer to your question (2).

Here are some pointers to related discussions on the Tuscany wiki and 
the tuscany-dev list:
http://cwiki.apache.org/confluence/display/TUSCANYWIKI/Distributed+Runtime
http://www.mail-archive.com/tuscany-dev@ws.apache.org/msg18879.html
http://www.mail-archive.com/tuscany-dev@ws.apache.org/msg19105.html
http://www.mail-archive.com/tuscany-dev@ws.apache.org/msg18954.html

> These are just the initial set of points/questions that hit me when I
> thought about the integration. Jay /Raymond I guess you guys will be
> aware of many other points as well. Can you reply with your analysis
> so that we can flesh out the requirements completely in the mailing
> list. That way both the communities can contribute their thoughts. If
> you have already started can you just point me to where I can catch up
> on what has happened?
>
> Thanks
> Manu
>
> On 4/26/07, Raymond Feng <enjoyjava@gmail.com> wrote:
>> Hi, Geronimo community.
>>
>> As you may know, Tuscany is an Apache project under incubation to 
>> provide an
>> open source SOA infrastructure. For more information, you can visit
>> http://cwiki.apache.org/TUSCANY/.
>>
>> Tuscany implements the SCA specification (http://www.osoa.org) and 
>> allows
>> you to develop and run SCA components in various hosting 
>> environments. We
>> currently integrate with Tomcat and Jetty and would like to try to 
>> integrate
>> with Geronimo as well. I would like to start some discussions here to 
>> figure
>> out the best way to do that.
>>
>> After some preliminary investigations of Geronimo, I feel that there 
>> are two
>> options on the table so far.
>>
>> 1) Shallow integration: Package SCA applications together with the 
>> Tuscany
>> runtime as WARs and deploy them Geronimo as Web applications. It's 
>> basically
>> the integration with a Web container. We register a 
>> TuscanyContextListner
>> (which implements javax.servlet.ServletContextListener) in web.xml to
>> start/stop the Tuscany runtime when the web application is 
>> started/stopped.
>>
>> This will allow us to support the following use cases:
>> * A Web application hosted by Geronimo with business logic written as 
>> SCA
>> components
>> * Expose one or more SCA components as Web services over HTTP as 
>> supported
>> by the Web container.
>>
>> 2) Deep integration: We package the Tuscany runtime and its 
>> dependencies as
>> Geronimo modules and deploy them to Geronimo (which is similar to how 
>> Tomcat
>> is integrated as the Web container for Geronimo). We can then create a
>> Tuscany plugin (a collection of modules) so that it can be added to
>> Geronimo. The Tuscany container will then handle SCA-specific deployment
>> plans to install SCA applications and provide runtime infrastructure for
>> them.
>>
>> On top of Option 2, we could further integrate Geronimo's J2EE 
>> capabilities
>> such as EJB, WS, JMS and JCA with Tuscany. Basically, SCA components 
>> will be
>> able to access JEE services (using SCA composite references) and SCA
>> components will be able to expose services (SCA composite services) 
>> over JEE
>> protocols as well.
>>
>> This will allow us to support the following use cases:
>> * Any J2EE application hosted by Geronimo would be able to take 
>> advantage of
>> SCA programming model
>> * Provide SCA services over various protocols such as RMI/IIOP, JMS 
>> and JCA
>> * Invoke existing JEE applications (EJB, JMS backend, JCA-based EIS 
>> or Web
>> Services) from SCA components
>>
>> Any thoughts?
>>
>> Thanks,
>> Raymond
>> Apache Tuscany committer
>>
>>
>


-- 
Jean-Sebastien


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