Herein, rule-based handling of request for resource re-allocations provides for automated re-allocations, reducing the need for administrator intervention. The resources available to a reservation can be increased, decreased, or otherwise modified by forming and breaking selected connections between reservations and hosts. The rules herein determine which connections are to be formed or broken. Each rule associates a connection-modification criterion with a condition. In the event, the condition for a rule is satisfied by a reallocation request (and its context), the criterion is applied to the request plus its context to generate a list of connection modification plans. Each connection-modification plan identifies one or more connections between hosts and reservations to be formed or broken. Implementing the plan yields the desired re-allocation.