Why Choosing the Right SLI Matters More Than Setting SLO Targets

In a piece published on DEV Community, Dr. Samson Tanimawo argues that Service Level Indicators (SLIs) are more critical to reliability engineering than Service Level Objectives (SLOs). While SLOs are simply numerical targets teams choose, SLIs define what is actually being measured — and a poorly chosen metric can mask real user-facing failures. He illustrates this with a common pitfall: monitoring healthcheck endpoints that appear healthy even when core services like checkout APIs are broken. Tanimawo recommends measuring user-meaningful signals, such as whether checkout requests complete successfully, rather than superficial system checks. He concludes that most engineering teams work in reverse — setting SLO targets before validating their SLIs — which explains why reliability efforts often fail to improve actual user experience.