I see this
http://docs.sun.com/app/docs/doc/820-4341/abdjj?a=view which indicates you require 2 clusters to support what I described which is really a shame. Having to manage 2 clusters with a total of 4 instances seems like a lot of management in order to achieve what I was looking for. I saw some posts on supporting application versions I hope this very common use case of upgrading an application is given a bit more thought in that feature.
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