In this work, we investigate mechanisms to ensure that a shared data center can operate within a power budget, while optimizing a global objective function(e.g., maximize the overall revenue earned by the provider). We present the BrownMap methodology that is able to ensure that data centers can deal both with outages that reduce the available power or with surges in workload. BrownMap uses automatic VM resizing and Live Migration technologies to ensure that overall revenue of the provider is maximized, while meeting the budget. We implement BrownMap on an IBM Power6 cluster and study its effectiveness using a trace-driven evaluation of a real workload. Both theoretical and experimental evidence are presented that establish the efficacy of BrownMap to optimize a global objective, while meeting a power budget for shared data centers.