axum-impl-tracing

To add structured logging and distributed request tracing to an Axum service, install a tracing-subscriber globally in main and use tower-http TraceLayer::new_for_http to instrument HTTP requests, grouping spans by MatchedPath rather than raw URI to maintain correct cardinality.

Axum tracing spans nest incorrectly or interleave when holding Span::enter guards across await points. Use #[tracing::instrument] or Future::instrument instead to ensure async-safe span creation and proper parent-child relationships in your tracing output.

Configure RUST_LOG filtering and tracing-subscriber layers by using SubscriberExt and SubscriberInitExt to compose EnvFilter and fmt layers with .with()/.init() methods, ensuring the global subscriber is installed exactly once in main to prevent startup panics.

Yes, you can export Axum tracing spans to an OpenTelemetry backend by composing tracing-opentelemetry onto the same subscriber registry, configuring a matching OTLP pipeline to send distributed traces to platforms like Jaeger, Tempo, or Grafana.

The correct way to emit structured tracing events in Rust async handlers is to declare span fields before recording and use tracing::info!/error! macros with key/value field sigils like %/?, avoiding format!-interpolated messages that reduce structured logging quality.