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SLI, SLO, and SLA

zex profile image Zex ・2 min read

SLI - Service Level Indicator

Defines a measure of service level provided by service providers.
Examples

  • Uptime of the service
  • Number of Transactions

SLO - Service Level Objective

Defines a target value or a target range of service level, measured by SLI.
Examples

  • Availability of the service should be 99.999%

SLA - Service Level Agreement

Defines a commitment between service providers and customers.
Examples

  • Refund service fee
  • Provide free service for a period of time

The Nines

Percentages to measure the service.

Availability % Downtime per year Downtime per month Downtime per week Downtime per day
55.5555555% ("nine fives") 162.33 days 13.53 days 74.92 hours 10.67 hours
90% ("one nine") 36.53 days 73.05 hours 16.80 hours 2.40 hours
95% ("one nine five") 18.26 days 36.53 hours 8.40 hours 1.20 hours
97% 10.96 days 21.92 hours 5.04 hours 43.20 minutes
98% 7.31 days 14.61 hours 3.36 hours 28.80 minutes
99% ("two nines") 3.65 days 7.31 hours 1.68 hours 14.40 minutes
99.5% ("two nines five") 1.83 days 3.65 hours 50.40 minutes 7.20 minutes
99.8% 17.53 hours 87.66 minutes 20.16 minutes 2.88 minutes
99.9% ("three nines") 8.77 hours 43.83 minutes 10.08 minutes 1.44 minutes
99.95% ("three nines five") 4.38 hours 21.92 minutes 5.04 minutes 43.20 seconds
99.99% ("four nines") 52.60 minutes 4.38 minutes 1.01 minutes 8.64 seconds
99.995% ("four nines five") 26.30 minutes 2.19 minutes 30.24 seconds 4.32 seconds
99.999% ("five nines") 5.26 minutes 26.30 seconds 6.05 seconds 864.00 milliseconds
99.9999% ("six nines") 31.56 seconds 2.63 seconds 604.80 milliseconds 86.40 milliseconds
99.99999% ("seven nines") 3.16 seconds 262.98 milliseconds 60.48 milliseconds 8.64 milliseconds
99.999999% ("eight nines") 315.58 milliseconds 26.30 milliseconds 6.05 milliseconds 864.00 microseconds
99.9999999% ("nine nines") 31.56 milliseconds 2.63 milliseconds 604.80 microseconds 86.40 microseconds

Source: Wiki

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