An nginx access log records request information when logging runs at the end of processing. The selected fields can distinguish what the client requested, which URI ultimately handled it, what response was sent, and what happened during upstream attempts. These are different observations. A useful format keeps them separate instead of assuming that one status, duration, or path explains the whole request by itself. ...
A distributed trace connects recorded operations through a shared trace identifier and explicit relationships. A span represents one operation, with start and end timestamps, attributes, events, and status. This makes a trace useful when a checkout request crosses an application, an inventory service, and a payment service. The resulting picture depends on which operations were instrumented, retained, and exported; it is not an automatic inventory of every action the request performed. ...
A metric named request_duration leaves readers guessing whether 250 means seconds, milliseconds, or something else. A Prometheus-facing name such as http_request_duration_seconds carries that contract into queries, recording rules, and alerts. The contract still needs a correct implementation. Appending _seconds to measurements collected in milliseconds changes the spelling, not the magnitude, and can create a thousandfold monitoring error. ...
Prefer a verifiable sentence over a colored panel when the claim has to survive an audit.