What is Observability?
Observability is how well you can understand what a running system is doing from the outside, through logs, metrics, and traces. Good observability means that when something breaks, you can find out why in minutes instead of guessing.
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Why it matters
Software fails in production in ways no test anticipated. Observability is the difference between a quick, confident fix and an outage spent reading code and hoping.
In practice
Logs tell you what happened, metrics tell you how much and how often, and traces follow a single request across the system. Wiring these in early is cheap; retrofitting them during an incident is not.