With an increase in the usage of data centers to power content distribution networks (CDN), minimizing the cost of deployment while handling fault-tolerance has become an important research issue. In this work, we demonstrate the importance of cost-aware capacity provisioning in fault-tolerant CDN data centers (that can tolerate failure at a single site). We propose an optimization model that exploits spatio-temporal variation in the electricity price and demand to minimize the total cost of ownership. We use real-world data to show that the cost reduction can be upto 40% compared to the existing model, which minimizes the expected response time by routing requests to a nearby data center.