axum-core-architecture

Axum's layered architecture maps tokio for async runtime, hyper for HTTP, tower for services and middleware, and Axum for routing, extraction, and handler dispatch. Each layer owns specific responsibilities during the request lifecycle.

Axum handler compilation failures often stem from unsatisfied async Send constraints or missing FromRequest trait bounds. Using the #[debug_handler] attribute transforms cryptic trait-bound errors into actionable diagnostic messages.

Use axum::serve as the server glue by passing a Router treated as a tower::Service. It requires a bound listener input and never returns normally, serving as the unified entry point without version splits.

Depend on axum-core instead of axum when authoring libraries that implement FromRequest, FromRequestParts, or IntoResponse. This avoids pulling unnecessary routing and server components, keeping library dependencies lightweight.

Debug an Axum server that exits immediately by verifying the axum::serve binding configuration and ensuring the tokio runtime stays active. Because axum::serve never returns normally, immediate exits indicate runtime or listener binding misconfigurations.