At New Relic, we have customers that scale Rails apps well over 100k requests per minute. They also have the advantage of understanding how their app scales (th

At New Relic, we have customers that scale Rails apps well over 100k requests per minute. They also have the advantage of understanding how their app scales (throughout, cpu, memory at various levels of load) and how they are utilizing their infrastructure. Check out http://newrelic.com http://newrelic.com - We have a week-long free trial of our premium service and a forever-free version with less features as well. As far as what architecture/infrastructure is required to support certain levels of traffic, it really depends. However, the faster your app, the fewer app instances you need to serve a given amount of traffic.