A methodology for designing data center infrastructure for E-commerce sites is developed. It differs from existing methodologies in that it evaluates and compares alternative designs from a business perspective, that is, by evaluating the business impact (financial loss) imposed by imperfect infrastructure. The methodology provides the optimal infrastructure that minimizes the sum of provisioning costs and business losses incurred during failures and performance degradations. A full numerical example design is provided and results are analyzed. The use of the method for dynamically provisioning an adaptive infrastructure is briefly discussed.