1. In a distributed computing environment, a method of defragmenting a cluster service to service additional capacity requests on the cluster service, the method comprising: ranking a plurality of servers in a cluster by currently available capacity; based at least on the ranking, selecting a first server with the most currently available capacity; identifying one or more replicas from the first server to move to a second server; determining the identity of the second server by at least identifying, from the ranking of the plurality of servers in the cluster, a server with a least currently available capacity that is sufficient to host the one or more identified replicas to be moved from the first server; and moving the one or more identified replicas from the first server to the second sever.