High availability

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.

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.

Following the industry standard

Generally speaking, the more complex a system, the more things can go wrong; this translates to a lower availability. In other words, it is much easier to have a 100% uptime for a static website than for an API.

So, what is the industry standard for availability for common APIs? Most online platforms offer a service level agreement (SLA) that includes a clause for the minimum availability of the platform. Here are some examples (accurate at the time...