We have two standalone OS instances into two different organizations each one of them have some of their own operations to service.

Both of these two instances have a huge amount of resources available at this period. We would like to setup these two, into one federated meta-cloud under these conditions :

Any Infrastructure may have private resources, users and management and operations. Any infrastructure may be unplugged at any time, with 0 notice from the federation (or modify the shared resources), but keep the private ones up & running. Avoid the most possible configuration from those infrastructures, and implement most of the operations into a 3rd one, that will work as a broker or load balancer or resource alocator.

Have you ever implemented something like that ? Do you have any software to suggest me ? Any good / bad practices ?