In designing complex systems, Engineers, Developers and Systems Architects always have to make quantitative assumptions in order to satisfy anticipated loads and expectations of the final product. Many questions are asked before any complex system design that relate to systems performance, infrastructure and components configuration, behavior prediction and bottlenecks fixes. All these questions can be answered using modeling and simulation tools that allow engineers to predict systems behaviors in different settings and optimize systems in production by identifying bottlenecks and flaws in the infrastructure or workflow.