[mod_cluster-dev] Enabling mod_cluster by default in AS6

[Bela Ban]

Paul Ferraro wrote:
> 1. If a user deletes mod_cluster.sar from their profile, jbossweb will
> refuse to start since it has a dependency on the ModClusterListener bean
> - the configuration of which was just deleted. This is rather annoying.

Maybe this is a general MC question for smart Ales :-) If we have a 
dependency on a non-existing bean, can't we just ignore that dependency 
? For example, if we read in all the beans at MC startup time, construct 
a dependency graph and see that the ModClusterListener bean doesn't 
exist, can't we ignore that dependency ?


The other question I have for Paul, is why does jbossweb have a 
dependency on ModClusterListener ? Can't ModClisterListener simply query 
JBossWeb (if available) for deployed contexts (if that's why it 
registered as a listener) and then register if needed ?

If we could remove this dependency, we'd have one less thing to worry 
about (and configure)...

> a. A potential workaround for this: move the mod_cluster jar and
> configuration xml within the jbossweb service itself, rather than a
> separate deploy/mod_cluster.sar. Those profiles that include jbossweb,
> but do not want to include mod_cluster could include a "dummy"
> ModClusterListener bean configuration - so the dependency is satisfied.

Hmm, not really nice though...


> b. Hmm - now that I think of it we may actually be able to drop the
> jbossweb dependency altogether... 


YEEEAAAHHH !

> The reason this dependency exists in
> the first place is to ensure that mod_cluster sends the necessary
> DISABLE-APP/STOP-APP/REMOVE-APP mcmp messages prior to shutdown of
> jbossweb. In my fix for MODCLUSTER-131, mod_cluster's shutdown handling
> was enhanced to react to the "jboss.tomcat.connectors.stopped" JMX
> event, emitted prior to stopping the Connectors, which is the first
> thing jbossweb does during shutdown. If I'm not mistaken, this may
> ultimately mean that we can finally let mod_cluster depend on jbossweb,
> and not the other way around.

That's how it should be (see my comment above) !


> We still need mod_cluster to start before the WebServer

Why ? Can't we simply grab the deployed contexts from JBossWeb ? If 
mod-cluster is started before jbossweb, we'll get the deployed contexts 
later, once jbossweb has been started. Do we get notifications about 
when beans have been started ? If so we could listen for 
jbossweb-started, and *then* grab all contexts...



-- 
Bela Ban
Lead JGroups / Clustering Team
JBoss