Counting the Nines

Internet infrastructure is rated by its uptime — and engineers obsess over the nines. A facility promising 99.99% uptime can be down for less than 53 minutes a year. Add one more nine, 99.999%, and the budget shrinks to roughly five minutes a year.

The biggest vulnerability is concentration. Three companies — Amazon, Microsoft, and Google — control roughly 65% of cloud infrastructure. A failure at any one of them cascades across millions of services simultaneously.