A computer-implemented method and system of testing and maintaining outage resilience of server resources of a server infrastructure by means of a hybrid simulation is presented. The server infrastructure comprises a plurality of servers executing a plurality of applications and the method comprises measuring a processor utilization for each of the servers of the server infrastructure, determining a resilience ratio of the server infrastructure by simulating the outage of at least one of the servers based on the measured processor utilization, and in response to the resilience ratio of the server infrastructure falls below a resilience threshold, initiating an assignment of additional resources for executing at least one of the plurality of applications to the server infrastructure.