A method for simulating a computer system includes defining a set of building blocks including models of components of the computer system. The set of building blocks is interconnected to produce a topological model of the computer system. A client transaction model is derived based on historical data, for generating simulated client requests to be processed by the topological model. A resource requirement model is produced based on the topological model and on the historical data, the resource requirement model simulating a resource utilization of the components of the computer system responsively to the generated client requests. A performance metric of the computer system is estimated by simulating the computer system using the simulated client requests and the resource requirement model.