What One More Nine Actually Costs You in Minutes

Subtitle: A nine is a downtime budget.

• Left column - Budget per year:
• 99% = 3 days 15 hours
• 99.9% = 8 hours 45 min
• 99.99% = 52 min 34 sec
• 99.999% = 5 min 15 sec
• Less than one careless deploy

• Right column - What a nine costs:
• Each nine cuts the budget by 10
• Engineering cost rises far faster
• Not 'can we be more available'
• Ask 'what is this nine worth'
• Buy a nine only where it pays

• Nines multiply down the chain:
• Your 99.9% is only a ceiling
• 4 sync deps at 99.9% drag it down
• Composition alone costs 0.7 nines
• Remedy: timeouts, fallbacks, async

• Simple difference:
• 0.999 ^ 5 = 99.5% = 2.3 nines
• 8h 45m budget becomes 1d 19h 43m

• Quoted about the wrong thing:
• Per month 99.9% = 43 minutes
• Per year 99.9% = 8h 45m
• Same SLA, 12x stricter window
• It is an average over requests
• One dead region hides in green

Sticky note - Honest test:

- Compute your nines from raw request logs, per region. Compare that with the dashboard headline.