SLO Adoption and Usage in Site Reliability Engineering

Chapter 4. Constructing SLIs to Inform SLOs

Once you choose the service(s) you want to measure, you can then think about the SLIs you will use to measure users’ common tasks and critical activities. In our experience, choosing SLIs that represent the customer’s experience and obtaining accurate SLI measurements are two of the most difficult tasks that organizations undertake on their SRE journeys.

The SLO Adoption and Usage Survey found that most organizations (87%) use availability as an SLI. Although availability is an important SLI, it should not be the only SLI you use to measure the reliability of your service. Request latency and error rate are also important metrics indicative of system health. Depending on your service, durability and system throughput should also be considered as metrics.

We are encouraged to see that organizations that adopted SLOs within the last year were the most likely to implement all types of SLI metrics. The industry has long relied on “uptime” as the measure of reliability when, in fact, measuring only time “up” or “down” obscures many important details. Relying on uptime as the measure of reliability is particularly problematic in distributed and cloud computing environments, where systems are usually not binary “up” or “down,” and outages are the result of partial degradation with symptoms that are more diverse than “not working.”

We hope that the information provided in this chapter will help organizations select the best SLIs for their ...