A controller is provided for a Cloud based service handling multiple types of traffic in a telecommunications network, the controller comprising: a first stage configured to automatically model use of Cloud resources allocated to the service for specific workloads of each of a plurality of traffic types, so as provide a variety of models for each traffic type; a second stage configured to automatically reduce the number of and generalise the models so as to provide generalised models for each traffic type applicable to other workloads than the specific loadings; a third stage configured to automatically evaluate accuracy of the generalised models for various combinations of given workloads, in each combination each of the given workloads being of a corresponding traffic type, and to select one of the generalised models dependent upon evaluated accuracy; and a fourth stage configured to control operation of the Cloud resources according to the selected model.