An SLI is a type of metric that allows us to quantify the perceived quality of a service from the perspective of the end user. Let's take a look at some common types of SLIs that can be applied to cloud-based services:
- Availability is defined as the ratio of two quantities: the time that the service can be used by the end user/customer and the total time that the service is deployed (including any downtime). For example, if we were operating a service that was offline for maintenance for about 53 minutes over the course of the last year, we could claim that the service had 99.99% availability for the same period.
- Throughput is defined as the number of requests that a service processes in a given time period (for example, requests per second).
- Latency is yet another interesting SLI and is defined as the time it takes for the server to process an incoming request and return a response to the client.