Finally, your shiny app gets noticed by media and a praise piece is published on a high-traffic website. Thousands and thousands of new visitors start pouring in. Unfortunately, your backend is not prepared to handle the load. It goes under not capturing even 1% of them. Your have just been “slashdotted”.
To tackle the effect, the industry wisdom suggests having a 10x bigger infrastructure right in the beginning. It is fine you are ready to pay more but you still miss the spike that will require 20x the server capacity.
Erlang on Xen can spawn new instances in under 100ms, scaling up while the spike is already under full swing. Your infrastructure may balloon to hundreds and thousands of instances to absorb the load and then scale down (to zero) in minutes to keep the infrastructure costs in check.