[jboss-as7-dev] Clustered invocation design

[Scott Marlow]

>
> Summary
> -------
>
> For both options, we have to determine an appropriate load-balancing
> strategy.  The choice of direction will affect how our clustering and
> transaction interceptors function.  We also have to suss out the logic
> around dealing with conflicting or wrongly-ordered topology updates;
> hopefully our existing policies will continue to apply.
>

I just wanted to mention, that when we talk about load-balancing 
strategies/policies, that we might need some strategies that can handle 
affinity for groups derived from extended persistence.  In other words, 
this would be a policy that understands how to migrate a group of 
stateful session beans to the same target node, during fail-over.

A simple example would be for two stateful session beans (SFSB1 + 
SFSB2), that share an extended persistence context (XPC1).  When an 
instance of SFSB1 fails-over to a new cluster node, the corresponding 
SFSB2 instance should fail-over to the same target node.

Another example, would be the same as above, except SFSB2 has a 
reference to SFSB3, which has a different XPC3.  XPC3 is also used by 
SFSB4.  So, the load balancing policy would be need to have some 
heuristic or maybe group-id that covers this case.

One reason for ensuring that the same node is chosen for groups derived 
from use of extended persistence context, is so that applications can 
continue to see dirty data that is associated with the XPC.