The private cloud expands and contracts resources nearly instantaneously and doesn't rely on a public cloud for extra capacity. Imagine the kind of infrastructure needed for a website fielding 1.5 million requests per second. That was one of the challenges faced by Yahoo’s Todd Papaioannou, vice president of cloud architecture. “What’s my biggest pain spot? No, it’s not Google,” he recently quipped with attendees during his keynote speech at the Cloud Leadership Forum, held last month in Santa Clara, Calif. “My biggest problem is elasticity. VM spin-up time. Virtualization isn’t there yet.” Ten to 20 minutes is just too long to handle a spike in Yahoo’s traffic when big news breaks such as the Japan tsunami or the death of Osama bin Laden or Michael Jackson. RESEARCH: Public cloud vs. private cloud: Why not both? That’s why Yahoo has built itself the ultimate private cloud. And by private cloud, we don’t mean just a cluster of virtualized servers — we mean an infrastructure that can expand or contract as quickly as you can take a deep breath and exhale. To continue reading, register here and become an Insider. You’ll get free access to premium content from CIO, Computerworld, CSO, InfoWorld, and Network World. See more Insider content or sign in. Cloud Computing