Half of the pundits claim that The Cloud is the future. The other half warn one that Big Data is coming. Real engineers know these two don't always marry easily. How do they build systems that really scale, inside or outside the cloud? What conventional approaches don't work? What new approaches are available? What must they sacrifice from using them, and what do they gain in return? How do the economics really shake out? What does the CAP theorem really mean? Which things one have heard about the cloud are just hype, and which are really revolutionary?