Availability is a measure of the proportion of time that a system is able to fulfill its intended function. For an API, it means the percentage of time that the API can respond correctly to a client's requests.
High availability
Measuring availability
Availability is usually measured as the percentage of time the system is functional (Uptime) over the total elapsed time:
This is typically represented as "nines". For example, a system with an availability level of "four nines" will have an uptime of 99.99% or higher.
