[jboss-dev-forums] [Management Development] - To scope or not to scope (domain.xml)

[Brian Stansberry]

Brian Stansberry [http://community.jboss.org/people/bstansberry%40jboss.com] replied to the discussion

"To scope or not to scope (domain.xml)"

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> Jason Greene wrote:
> When you think about it, a server-group, and a cluster are really the same thing, the only difference is that the cluster has an additional set of services that a basic group does not.

Yes, but isn't the set of capabilities that a server has defined by its profile? We could say that defining a server as part of a cluster means that additional capabilities are added beyond what's in the profile. But then we are dividing the definition of a profile into two places. Also, exactly what capabilities should be added if a server is in a cluster is unclear.

A very simple concept of a cluster is that it is a server-group that also exposes some predefined configuration properties that need to be kept consistent throughout the group. (A server-group would not have such properties by default, although users could add custom ones.) Things such as:

* Group name (current -g)
* Type of intra-group communication to use by default (udp, tcp)
* Default interface to use for intra-group communication
* Default multicast address to use
* other defaults less commonly changed

A cluster might also have some management capabilities besides what is available to a server-group, although I'm not sure what. It should be possible for example to perform a (rolling) redeployment to a server-group.

A separate discussion is how communication will occur between servers who are not members of a cluster. There needs to be a group communication mechanism that spans the entire domain.
> This was what I meant by the cluster-service tag, a way to specify how a group would cluster a particular service (maybe not all services should be clustered). Although it was just something I through out there as an example. A better way likely exists

Currently how we cluster a particular service is defined in that service's configuration, it's not something applied externally. And the details of what needs to be configured are often disparate between different services, so I'm not sure those configs can profitably be externalized into some common configuration element.

Ah, or are you talking about "clustered-service" as a wrapper to describe how to manage the service, e.g. how to (re)deploy across cluster?

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