Service-Level Indicator
SLI 是服务级别监控，直接表明服务的状态的某一方面，历史的数据将用于计算 SLO。
一个好的 SLI 应当站在用户的角度观察服务，比如“网页加载速度”。
Google
We also have a direct measurement of a service’s behavior: the frequency of successful probes of our system. This is a Service-Level Indicator (SLI). When we evaluate whether our system has been running within SLO for the past week, we look at the SLI to get the service availability percentage.[1]
Reliability & Metrics
SLI, or Service Level Indicator, represents a measurement of a service’s behavior. A good SLI measures your service from the perspective of your users. An example SLI can be the speed at which a web page loads.[2]