Observability is often sold as a vendor category, but at its core it is a property: can you understand system behavior from external signals without redeploying code? For systems engineers, that spans kernel metrics, service golden signals, and business KPIs that actually move when infrastructure degrades.
Metrics tell you velocity; logs tell you story
High-cardinality explosions are real, but so is the pain of an alert that says “slow” with no attributes. Invest in consistent labeling—environment, service, version—and structured logs that correlate with trace IDs where possible. The goal is a timeline a new responder can follow.
Tracing closes the loop
In full stack systems, a user-visible stall might begin in DNS, accelerate in a connection pool, and finish in a thundering herd on a database replica. Traces bridge those layers. They are not free to operate, but neither is guessing.