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 of writing):

• Google Compute Engine Service Level Agreement (SLA): 99.99%
• Amazon Compute Service Level Agreement: 99.99%
• App Engine Service Level Agreement (SLA): 99.95%
• Google Maps—Service Level Agreement (“Maps API SLA”): 99.9%
• Amazon S3 Service Level Agreement: 99.9%

Evidently, these SLAs provide minimum availability guarantees that range from "three nines" (99.9%) to "four nines" (99.99%); this translates to a maximum downtime of between 52.6 minutes and 8.77 hours per year. Therefore, we should also aim to provide a similar level of availability for our API.