Observability Explained: Metrics, Logs, and Traces Are Three Distinct Mechanisms

Modern observability is commonly mistaken for an advanced form of logging, but the two differ fundamentally in how data is emitted rather than how it is analyzed. Metrics are counters held in application memory and periodically scraped or flushed, meaning a million requests generate one counter value rather than a million records. Logs function as discrete events enriched with a trace ID that acts as a linking key across services. Distributed tracing works by copying that trace ID into outgoing request headers at each service hop, allowing a backend to later reconstruct the full request path from independently exported spans. Because the trace ID must be propagated at request time, no retrospective log analysis can substitute for instrumentation built into the request path itself.