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