The ResourceManager strikes a balance between cluster utilization and strict enforcement of resource invariants in the cluster. Individual allocations of containers must be reclaimed- or reserved- to restore the global invariants when cluster load shifts. In some cases, the ApplicationMaster can respond to fluctuations in resource availability without losing the work already completed by that task (MAPREDUCE-4584). Supplying it with this information would be helpful for overall cluster utilization . To this end, we want to establish a protocol for the RM to ask the AM to release containers.