SLIs, SLOs and burn-rate alerting
An SLI measures a user-facing outcome, not a resource internal - CPU utilization is not a service level indicator. SLOs turn that measurement into a target, error budget consumption turns the target into a priority, and burn-rate alerts are what page a human, so paging is tied to user impact instead of threshold noise. Data pipelines get freshness SLOs for the same reason: a silent stall produces no error. Measure first - SLOs are what focus reliability work.