Request for a new lease type: the fair-share lease

Currently OpenStack allows just a static partitioning model where the resource allocation to the user teams (i.e. the projects) can be done only by considering fixed quotas which cannot be exceeded even if there are unused resources (but) assigned to different projects. Therefore in a scenario of full resource usage for a specific project, new requests are simply rejected. Past experience has shown that, when resources are statically partitioned (e.g. via quota) among user teams, the global efficiency in the Data Center's resource usage is usually quite low (often less than 50%).
This issue could be addressed by BLAZAR by extending (if possible) the list of the supported lease types. In particular we (the Italian National Institute for Nuclear Physics) would like to add a new lease type to support this specific use case. The idea is to give a lease to the unused resources just for a limited time duration (e.g. from few hours to 1 day). Let's suppose that the project "A" has consumed all its assigned resources while the project "B" has several available resources. "B" may offer its own resources to "A" just for a limited and well known time duration (i.e. not forever) so that in the future it can claim, if needed, the available resources provided to "A". This allows to implement a fair-share mechanism which guarantees that the resources usage is equally distributed among users and projects by considering the portion of the resources allocated to them (i.e. share) and the resources already consumed. Please note that the "share" is a different concept than "quota" in the cloud terminology. You can consider this proposal as a way to update dynamically the quotas by considering the historical usage of each project. This approach should improve OpenStack in terms of efficiency for resource utilization.