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