Technology for computing number of active servers needed over time in a cloud/compute cluster includes the following operations (not necessarily in the following order): (i) determining the capacity of each VCE provisioned on the cloud against the resource guaranteed to that VCE; (ii) forecasting the resource needs over time using historical requests for each VCE flavor; and (iii) using the forecasted resource needs to determine the required number of future servers at some future time. Some embodiments of the present invention use a formula that accounts for the interplay among various parameter values of the VCE flavors and also the mapping of the needs of VCEs of various flavors to the capabilities of physical resources.