Pinterest architecture - $39,000 per month for 410 TB data in S3
Pay for what you use saves money. Most traffic happens in the afternoons and evenings, so they reduce the number of instances at night by 40%. At peak traffic $52 an hour is spent on EC2 and at night, during off peak, the spend is as little as $15 an hour.
150 EC2 instances in the web tier
90 instances for in-memory caching, which removes database load
35 instances used for internal purposes
70 master databases with a parallel set of backup databases in different regions around the world for redundancy
Written in Python and Django