Availability (also known as service availability) is a metric commonly used to quantitatively measure reliability.

  • Availability is the percentage of time a workload is available for use.

This percentage is calculated in periods such as a month, a year, or the last three years. Applying the strictest possible interpretation, availability decreases whenever the application is not operating normally, including scheduled and unscheduled outages.

The following is a table of common application availability design goals and the maximum duration of outages that can occur in a year without the goal being reached. The table contains examples of common application types at each availability level.

Availability Objective Max. Unavailability (by year) RTO # of Regions Application Type
90% 36 days and 12 hours 4 - 24 hours One .
95% 18 days and 6 hours 4 - 12 hours One .
99% 3 days and 15 hours 2 - 8 hours One batch processing tasks, data analysis
99.9% 8 hours 45 minutes 1 - 4 hours One a company’s internal tools
99.95% 4 hours 22 minutes 30 - 120 minutes One or more Online trade, point of sales
99.99% 52 minutes 5 - 20 minutes Two or more Video delivery
99.999% 5 minutes 1 - 60 seconds Two or more Financial Transactions

Use the table above as a reference to create the version tailored to the needs of your applications. Regardless of the recovery strategy chosen, it cannot exceed the Recovery Timeout (RTO).