In the same JVM, we now use a singleton object to keep all the metadata for
the deployable composites running on the node. This has been proven to be
problematic, especially in the case of Tomcat or Geronimo integration where
applications are running in isolated address spaces. The partition is the
portion of SCA domain visible to a given address space and its lifecycle is
the same as an Web/JEE application (or some other modules).
Then we have the following hierarchy:
SCA domain (accross multiple nodes on the network)
--- SCA node (I assume one node per JVM and one JVM per node)
--- SCA partition (I assume one partition per address space in the
JVM)
Thanks,
Raymond
----- Original Message -----
From: "Simon Laws" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, August 31, 2007 9:46 AM
Subject: Re: Rationalizing SCA Domain implementations
On 8/31/07, Raymond Feng <[EMAIL PROTECTED]> wrote:
Hi,
Comments inline.
Thanks,
Raymond
----- Original Message -----
From: "Simon Laws" <[EMAIL PROTECTED]>
To: "tuscany-dev" <[email protected]>
Sent: Thursday, August 30, 2007 9:13 AM
Subject: Rationalizing SCA Domain implementations
> We now have a number of domain implementations in Tuscany Java SCA
> including
>
> - The SCADomain interface
> - DefaultSCADomain
> - EmbeddedSCADomain
> - HotUpdatableSCADomain
> - DistributedDomain/Node
>
> Covering a number of scenarios
>
> - running a domain in a single node
> - running a domain across multiple nodes
> - Adding, removing, updating the contributions of a domain through the
API
> and automatically
> - Activating/deactivating, starting/stopping deployable composites
through
> the API
> - Starting, stopping components through the API
> - Locating service in the domain through the API
> etc.
>
> There are some scenarios that we don't cover at the moment
>
> - running multiple domains in a VM
Why does one JVM want to join multiple SCA domains? IMHO, it might be
over-engineered.
I think this depends on the answers to you second point.
What else?
>
> I would like to propose that we rationalize these various
implementations
> down to a more manageable number. I have a simple model in my mind of
the
> building blocks we have to deal with.
>
> 1/ The node.
> Is responsible for running segregated domains in a VM
> Associated with zero or more domains.
I think we probably miss another layer here, the 'partition's in the same
node. In a typical server hosting environment such as Tomcat or Geronimo,
applications are isolated by address spaces (such as ClassLoader for java
classes). The list of deployable composites coming from the same address
space will form a partition. With this layer, we can better embed Tuscany
to
the various hosting environment and provide the flexibility for dynamic
updates.
With this in mind, the node will have an aggregate view of all the
partitions within the node.
Can you say some more about what a "partition" is in the context of SCA?
Asking the question in a different way, what is the implication of having
multiple "partitions" in the same domain? Is this like having separate
nodes
but with more efficient cross node comms mechaninsm, i.e. within the same
JVM?
2/ The domain.
> Logically knows about all of the artifacts of a domain.
> Associated with one or more (in the distributed case) nodes.
> A local representation of the domain (the SCADomain object) provides
the
> interface to wider domain
>
> There are some subtleties here about the timing of associating a domain
> with
> a node(s) but the simple case, which we implement at the moment,
> is if you start a domain, start a node, associate the two together and
> then
> add contributions. The contributed components run on the node with
> which
> the local domain object is associated (more complex node/component
> selection
> algorithms can be imagined but we don't do this at present).
>
> Here are some suggestions based on the interfaces from the list of
> existing
> domain classes above, of the kind of things we need to be able to do;
>
> Domain
> Create/destroy the domain based on its URI
> Act of creating a domain object with a globally unique URI means
> that
> it
> becomes part of that domain and can scope comonent invocations in
> the context of that domain.
> There should be a default hot update location if we want to maintain
> that feature.
> Contribution management
> Add/remove contributions
> Resulting composites/components sit ready to be started
> Composite Management
> Start/stop composite
> Akin to adding a composite to the domain composite and activating
it
> Not sure how we identify a composite to be activated - by
> composite
> name? Currently it's done with a reference to the composite object
> Do we need to expose separate activation operations?
> Component Management
> Start/stop component
> Add.Remove listener
> Not sure how the listener from the current interface is going to
> be
> used
> getComponentInfo
> There are some existng related component management interfaces here
> also
> LocateService
> public abstract <B, R extends CallableReference<B>> R cast(B
target)
> public abstract <B> B getService(Class<B> businessInterface,
> String
> serviceName);
> service name -> component name / service name
> public abstract <B> ServiceReference<B>
getServiceReference(Class<B>
> businessInterface, String referenceName);
>
> We also need the domain to provide some systematic interfaces to
support
> distributed operation, for example,
>
> ServiceDiscovery
> register/find service endpoint
>
> Node
> Create/destroy the node based on its URI
> Add/remove an association with a domain
> start/stop a nodes activity
>
> Currently we have an approach, with the EmbeddedSCADomain, where the
class
> vends a series of management interfaces, contribution, model building
etc.
> for performing actions on the domain. This is useful as it allows
> flexibility in how these management actions are implemented without
> changing
> all
> of the domain implementation. It would also be appropriate, in the
future,
> to expose some of these interfaces as services to allow for remote
> management of the
> domain at a node.
>
> Would welcome thoughts about this generally. Also specifically do we
need
> to
> maintain the detailed interfaces provided with EmbeddedSCADomain
alongside
> this.
>
> Regards
>
> Simon
>
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