Meaningful Availability

High availability is a critical requirement for cloud applications: if a sytem does not have high availability, users cannot count on it for their critical work. Having a metric that meaningfully captures availability is useful for both users and system developers. It informs users what they should expect of the availability of the application. It informs developers what they should focus on to improve user-experienced availability. This paper presents and evaluates, in the context of Google's G Suite, a novel availability metric: windowed user-uptime. This metric has two main components. First, it directly models user-perceived availability and avoids the bias in commonly used availability metrics. Second, by simultaneously calculating the availability metric over many windows it can readily distinguish between many short periods of unavailability and fewer but longer periods of unavailability.