What is the recommended approach for doing rolling upgrades in a JBoss cluster

Issue

• I have an environment with multiple nodes in a cluster, and I need to update some configuration files in each cluster node. What is the recommended approach to avoid a down time ?

• What is the recommended approach to upgrading a jboss cluster? We have a Singleton (which is NOT idempotent)  I can only think that in this case all nodes of the cluster must be fully stopped at the same time. Is there a best practice for these issues?

• Some say we shouldn't need to do a full cluster restart at all when the various .xml and java packages are changed. Is this ok? Are we at risk for any issues if we do this?

• I need to deploy a new version of an application to all nodes in the cluster and the changes are incompatible with the old ones.
• Can we set a flag on JBoss AS which tells the web server (load balancer) that its state (ready or not ready) and the web server will only connect to the node that is ready and running?
• How can we do rolling deployment without downtime in EAP 6 ?