Five Nines

ELI5 — The Vibe Check

Five nines means 99.999% uptime — 5.26 minutes of allowed downtime per year. The SLA everyone promises and almost nobody hits. That's not 5 hours. Not 5 days. Five minutes and 15 seconds of downtime in 365 days. Achieving it requires redundant everything, multi-region failover, chaos engineering, and a team that treats an incident at 3am like a sporting event. It's the gold standard that separates serious infrastructure from everyone else.

Real Talk

99.999% uptime (five nines) equates to 5.26 minutes downtime/year, versus 99.9% (three nines) which allows 8.7 hours. Achieving five nines requires active-active multi-region architecture, sub-second failover, zero-downtime deploys, and continuous chaos testing. Major cloud providers (AWS, GCP, Azure) offer SLAs in the 99.9–99.99% range for individual services. True five nines typically requires multi-cloud or multi-provider strategies for critical paths.

When You'll Hear This

"We're targeting five nines for the payments service. Everything else can be four nines." / "Five nines is a business requirement, not an engineering preference — price accordingly."