This document discusses Apache CloudStack performance testing using a simulator. It describes CloudStack as a platform for delivering IaaS clouds that is highly scalable and flexible. A typical CloudStack deployment architecture is shown. The challenges of creating a production-scale performance test environment are discussed when resources are limited in a QA lab. A simulator is presented as a solution to simulate thousands of hypervisors. Details of the simulator implementation and configurations used in test setups are provided. Metrics measured in benchmarks and future work ideas are outlined.