[jboss-dev-forums] [Design of POJO Server] - Re: profile service, farming

[bstansberry@jboss.com]

Been digesting this for a bit. :)

anonymous wrote : Synchronization of multiple local file based repositories as you describe is difficult for something outside of the profile service as the exact state of a deployment is the raw deployment content + any admin edits that may have occurred. Raw content sitting on the disk may not be in the profile depending on what removing a deployment from a profile actually does. 

I wasn't clear about one thing when I described that concept -- I was only thinking of that approach in terms of the basic.ProfileServiceImpl; i.e. an equivalent to VFSDeploymentScannerImpl that handles DeploymentPhase.APPLICATION_CLUSTERED. This is one reason  I considered it low priority. It doesn't fit with the full profile service impl, which works differently.

anonymous wrote : So 'hotdeployment' is purely a profile implementation detail, how we reconcile local repositories across a cluster would be part of the org.jboss.profileservice.spi.DeploymentRepository.getModifiedDeployments() implementation.

This part isn't clear to me. I certainly see how keeping different repositories in sync across a cluster is a detail of the repository implementation. And I can see how a cluster-aware DeploymentRepository instance could somewhat control when a ProfileImpl is aware of a change; e.g. don't make the profile aware of the change until all the repository instances in the cluster are aware of it.

But that doesn't get to controlling how the profile changes get reflected in the runtime.  That's a task of the MainDeployer and the deployers.

I'll talk about a specific ideal scenario:

An ear is deployed on all 4 nodes of a cluster. New version of the ear is deployed. Goal is that the ear be brought to a certain deployment stage (DeploymentStages.REAL?) on all nodes in the cluster such that we know the deployment will work on all nodes. A 2PC "prepare". At that point a cluster-wide "commit" is executed, the deployments are brought to the final stage where they handle requests, and the old version is removed.  If there is a failure during the "prepare", the new version is rolled back and the old version left in place.

There can be other variations on the above, but the main point is there is a multistep deployment process that requires intra-cluster communication at various points. Who controls that process is my question -- doesn't seem like its a concern of the DeploymentRepository, also doesn't seem like a proper concern of a deployer. My last post mentioned "some variant of the HDScanner concept" but that's not it either; you're right, HDScanner is just a trivial link between the profile and the MainDeployer and shouldn't be made into something else.  Seems like this is at least partly a concern of a cluster-aware MainDeployer.

anonymous wrote : The simple notion of having a deployment available across all nodes in the cluster, the DeploymentPhase.APPLICATION_CLUSTERED notion of the DeploymentRepository. There could be an annotation for this down to a bean level rather than a coarse deployment level. We could support this using the MetaDataRepository levels and have a clustered MetaDataRepository where we just distributed the BeanMetaData(for example) for the annotated bean. Provided the deployers/deployment attachments were properly integrated with the MetaDataRepository, it should just work, but there is a dependency issue.

This is the part I need to dig into more to get a better understanding of what you mean. Perhaps that will answer my question above. :)

anonymous wrote : Cluster wide dependencies between beans. Dependencies on components that are marked as @Clustered needs a cluster aware dependency implementation. Custom dependencies are supported by the mc, but the component deployers generating the component metadata have to generate the correct dependency implementation. 

Good point. This will be a nice thing to have.

This again has a coordination aspect; e.g. bean A on node 1 expresses a dependency on bean B that will be deployed on node2. If both A and B are known, cluster-wide, to the respository, you don't want A's deployment to fail with a missing dependency just because node 2's deployers haven't processed B yet.

anonymous wrote : Clustering like security is a cross cutting notion that we need the proper metadata for, and hooks to which cluster aware variations of the aspects can be applied.

Agreed. Right now the clustering metadata that exists is scattered, and it only exists for EJBs and web sessions. 

When I think in terms of priority order though, I'm thinking somewhat differently. To me, it's

1) Restoring some sort of ability to have repository information synchronized.  This is really the only thing the old farming did, in a half-assed way ;). I'd like to have this for 5.0.0.GA as I don't like taking something away, even if was half-assed.

2) Sorting out the "coordination" issue I've been talking about. The lack of that kind of coordination IMHO has always been the biggest weakness in the old FarmService.

3) Cluster wide dependencies. This could be done earlier if our solution for 1) ensures, following my example, that node 2's ProfileImpl knows about bean B before node 1's ProfileImpl knows about bean A.

4) Adding cluster-aware aspects to beans other than the existing JEE ones. Includes refactoring existing JEE clustered aspect impls to use as much of a common code base as possible.

Creating proper clustering metadata is an underlying task that occurs throughout the above.

View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4152982#4152982

Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&p=4152982