Uptime
Uptime is the proportion of time a system is serviceable, e.g., 99.99% = at most 4.32 minutes of downtime per month; a measure of availability.
Purpose
Quantify system availability, setting SLO/SLA targets.
Mechanism
Availability = uptime / (uptime + downtime). Counting nines: 99% (432m monthly downtime), 99.9% (43.2m), 99.99% (4.32m), 99.999% (0.432m). Measurement windows: rolling/fixed. Whether maintenance windows count.
Use cases
- Availability measurement
- SLO
- SLA