One embodiment is related to a method for determining an optimal resource configuration combination, comprising: (1) measuring performance of an application with a production resource configuration combination and its associated cost; (2) simulating historical workloads associated with the application with one or more candidate resource configuration combinations using idle resources; (3) selecting one of the candidate resource configuration combinations as a new production resource configuration combination based on cost and performance measurements and comparisons; (4) applying the new production resource configuration combination to a production environment; and (5) monitoring performance of the application with the new production resource configuration combination to confirm that it meets desired performance targets, wherein operations (1) to (5) are performed on a Platform as a Service (PaaS) platform.