Understanding SLIs, SLOs, and SLAs
Service-level objectives are part of a suite of other service-level acronyms, including service-level indicators (SLIs) and service-level agreements (SLAs). To try to explain it simply, SLIs are the lowest level of the three. They consist of individual, raw metrics (hint: this is where Prometheus will be helpful). For example, a count of error responses from your application. SLOs are comprised of one or more SLIs that, when taken together, form a meaningful measurement of performance measured on a scale of 0–100%. Generally, they are measured in “nines,” representing how many number 9s are in the percentage – 99.9% is three nines, 99.99% is four nines, and so on. An example SLO could be an objective that 99.9% of the requests to your application will be completed without an error. Finally, SLAs are SLOs with a contractual agreement thrown in. Generally, those contracts involve penalties (e.g., service credits) for failure...
