Minimal logging setup

axum uses the tracing and tracing-subscriber for logging so we need to include both.

[package]
name = "example-minimal-tracing"
version = "0.1.0"
edition = "2021"
publish = false

[dependencies]
axum = { path = "../../axum", features = ["tracing"] }
tokio = { version = "1.0", features = ["full"] }
tracing = "0.1"
tracing-subscriber = { version = "0.3", features = ["env-filter"] }

//! Run with
//!
//! ```not_rust
//! cargo run -p example-minimal-tracing
//! ```

use axum::{response::Html, routing::get, Router};
use tokio::net::TcpListener;
use tracing_subscriber::{layer::SubscriberExt, util::SubscriberInitExt};

#[tokio::main]
async fn main() {
    // minimal setup for logging
    tracing_subscriber::registry()
        .with(tracing_subscriber::fmt::layer())
        .init();

    let app = app();

    let listener = TcpListener::bind("127.0.0.1:3000").await.unwrap();
    tracing::debug!("listening on {}", listener.local_addr().unwrap());
    axum::serve(listener, app).await.unwrap();
}

fn app() -> Router {
    Router::new().route("/", get(handler))
}

async fn handler() -> Html<&'static str> {
    tracing::debug!("in handler");
    Html("<h1>Hello, World!</h1>")
}

When we start the application with cargo run we'll see line like this on the terminal:

2025-03-17T08:39:04.089621Z DEBUG example_minimal_tracing: listening on 127.0.0.1:3000

When we access the main page with a browser we'll see two more lines:

2025-03-17T08:39:27.044996Z TRACE axum::serve: connection 127.0.0.1:58560 accepted
2025-03-17T08:39:27.045345Z DEBUG example_minimal_tracing: in handler