Microservice Availability
Overview
Availability is measured in nines notation, which corresponds to the percentage of time that a service is available. A service that is available 99% of the time is said to have “two-nines availability.”
This notation is useful because it gives us a specific amount of downtime that a service is allowed to have. If your service is required to have four-nines availability, then it is allowed 52.56 minutes of downtime per year, which is 4.38 minutes of downtime per month, 1.01 minutes of downtime per week, and 8.66 seconds of downtime per day.
Here are the availability and downtime calculations for 99% availability to 99.999% availability:
99% availability: (two-nines)
- 3.65 days/year (of allowed downtime)
- 7.20 hours/month
- 1.68 hours/week
- 14.4 minutes/day
99.9% availability (three-nines):
- 8.76 hours/year
- 43.8 minutes/month
- 10.1 minutes/week
- 1.44 minutes/day
99.99% availability (four-nines):
- 52.56 minutes/year
- 4.38 minutes/month
- 1.01 minutes/week
- 8.66 seconds/day
99.999% availability (five-nines):
- 5.26 minutes/year
- 25.9 seconds/month
- 6.05 seconds/week
- 864.3 milliseconds/day