Rust 日志处理实战：从 tracing 到文件输出一步步优化

在 Rust 开发中，日志是调试和监控的重要工具。tracing 和 tracing-subscriber 提供了灵活而强大的日志处理能力，适用于从简单控制台输出到复杂分布式系统的需求。本文将通过一个 Axum 项目示例，带你逐步掌握日志的配置、优化以及文件输出，帮助你在实践中养成良好的日志习惯。

本文以一个基于 Axum 的 Rust 项目为例，介绍了如何使用 tracing 和 tracing-subscriber 实现日志记录。从基础的控制台输出开始，逐步优化代码以支持更详细的日志信息、异步任务耗时统计，最终实现日志文件滚动保存。通过四次迭代，我们展示了如何在实际开发中配置日志级别、添加文件输出并实时查看日志，适合 Rust 开发者参考。

Rust 日志处理

日志处理：tracing、tracing-subscriber

• tracing：记录各种日志
• tracing-subscriber：输出日志
• open-telemetry*：和 open-telemetry 生态互动
• 养成良好的 tracing/metrics 习惯

实操

项目目录结构

rust-ecosystem-learning on  main is 📦 0.1.0 via 🦀 1.85.0 via 🅒 base 
➜ tree . -L 6 -I 'target|coverage|coverage_report|docs'        


.
├── CHANGELOG.md
├── CONTRIBUTING.md
├── Cargo.lock
├── Cargo.toml
├── LICENSE
├── README.md
├── _typos.toml
├── cliff.toml
├── deny.toml
├── examples
│   ├── axum_tracing.rs
│   └── err.rs
├── rust-toolchain.toml
├── src
│   └── lib.rs
└── test.http

3 directories, 14 files

安装依赖

➜ cargo add axum --features http2 --features query --features tracing --dev       
➜ cargo add tokio --features rt --features rt-multi-thread --features macros --dev   
➜ cargo add tracing               
➜ cargo add tracing-subscriber --features env-filter 
➜ cargo add tracing-appender            

axum_tracing.rs 文件

use axum::{routing::get, Router};
use tokio::net::TcpListener;
use tracing::{info, instrument, level_filters::LevelFilter};
use tracing_subscriber::{
    fmt::{self, format::FmtSpan},
    layer::SubscriberExt,
    util::SubscriberInitExt,
    Layer,
};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let console = fmt::Layer::new()
        .with_span_events(FmtSpan::NEW | FmtSpan::CLOSE)
        .pretty()
        .with_filter(LevelFilter::INFO);
    tracing_subscriber::registry().with(console).init();

    let addr = "0.0.0.0:8080";
    let app = Router::new().route("/", get(index_handler));

    let listener = TcpListener::bind(addr).await?;
    info!("listening on {}", addr);
    axum::serve(listener, app.into_make_service()).await?;
    Ok(())
}

#[instrument]
async fn index_handler() -> &'static str {
    "Hello, world!"
}

第一次运行

cargo run --example axum_tracing

Finished `dev` profile [unoptimized + debuginfo] target(s) in 13.11s
    Running `target/debug/examples/axum_tracing`
2025-03-17T09:01:17.202968Z  INFO axum_tracing: listening on 0.0.0.0:8080
at examples/axum_tracing.rs:23

2025-03-17T09:13:39.480085Z  INFO axum_tracing: new
at examples/axum_tracing.rs:28
in axum_tracing::index_handler

2025-03-17T09:13:39.480445Z  INFO axum_tracing: close, time.busy: 5.67µs, time.idle: 368µs
at examples/axum_tracing.rs:28
in axum_tracing::index_handler

Request 发送请求

### index handler
GET http://localhost:8080/ HTTP/1.1

Response 响应

HTTP/1.1 200 OK
content-type: text/plain; charset=utf-8
content-length: 13
connection: close
date: Mon, 17 Mar 2025 09:13:39 GMT

Hello, world!

优化一 axum_tracing.rs 文件

use std::time::Duration;

use axum::{routing::get, Router};
use tokio::{net::TcpListener, time::sleep};
use tracing::{info, instrument, level_filters::LevelFilter, warn};
use tracing_subscriber::{
    fmt::{self, format::FmtSpan},
    layer::SubscriberExt,
    util::SubscriberInitExt,
    Layer,
};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let console = fmt::Layer::new()
        .with_span_events(FmtSpan::CLOSE)
        .pretty()
        .with_filter(LevelFilter::INFO);
    tracing_subscriber::registry().with(console).init();

    let addr = "0.0.0.0:8080";
    let app = Router::new().route("/", get(index_handler));

    let listener = TcpListener::bind(addr).await?;
    info!("listening on {}", addr);
    axum::serve(listener, app.into_make_service()).await?;
    Ok(())
}

#[instrument]
async fn index_handler() -> &'static str {
    sleep(Duration::from_millis(10)).await;
    let ret = long_task().await;
    info!(http.status = 200, "index handler completed");
    ret
}

#[instrument]
async fn long_task() -> &'static str {
    let dur = 112;
    sleep(Duration::from_millis(dur)).await;
    warn!(app.task_duration = dur, "long task done");
    "long task done"
}

第二次运行

优化二 axum_tracing.rs 文件

use std::time::Duration;

use axum::{routing::get, Router};
use tokio::{
    net::TcpListener,
    time::{sleep, Instant},
};
use tracing::{info, instrument, level_filters::LevelFilter, warn};
use tracing_subscriber::{
    fmt::{self, format::FmtSpan},
    layer::SubscriberExt,
    util::SubscriberInitExt,
    Layer,
};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let console = fmt::Layer::new()
        .with_span_events(FmtSpan::CLOSE)
        .pretty()
        .with_filter(LevelFilter::INFO);
    tracing_subscriber::registry().with(console).init();

    let addr = "0.0.0.0:8080";
    let app = Router::new().route("/", get(index_handler));

    let listener = TcpListener::bind(addr).await?;
    info!("listening on {}", addr);
    axum::serve(listener, app.into_make_service()).await?;
    Ok(())
}

#[instrument]
async fn index_handler() -> &'static str {
    sleep(Duration::from_millis(10)).await;
    let ret = long_task().await;
    info!(http.status = 200, "index handler completed");
    ret
}

#[instrument]
async fn long_task() -> &'static str {
    let start = Instant::now();
    sleep(Duration::from_millis(112)).await;
    let elapsed = start.elapsed().as_millis() as u64;
    warn!(app.task_duration = elapsed, "long task done");
    "long task done"
}

第三次运行

创建目录

➜ mkdir /tmp/logs        

优化三 axum_tracing.rs 文件

use std::time::Duration;

use axum::{routing::get, Router};
use tokio::{
    net::TcpListener,
    time::{sleep, Instant},
};
use tracing::{debug, info, instrument, level_filters::LevelFilter, warn};
use tracing_subscriber::{
    fmt::{self, format::FmtSpan},
    layer::SubscriberExt,
    util::SubscriberInitExt,
    Layer,
};

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let file_appender = tracing_appender::rolling::daily("/tmp/logs", "ecosystem.log");
    let (non_blocking, _guard) = tracing_appender::non_blocking(file_appender);

    let console = fmt::Layer::new()
        .with_span_events(FmtSpan::CLOSE)
        .pretty()
        .with_filter(LevelFilter::DEBUG);

    let file = fmt::Layer::new()
        .with_span_events(FmtSpan::CLOSE)
        .with_writer(non_blocking)
        .with_filter(LevelFilter::INFO);

    tracing_subscriber::registry()
        .with(console)
        .with(file)
        .init();

    let addr = "0.0.0.0:8080";
    let app = Router::new().route("/", get(index_handler));

    let listener = TcpListener::bind(addr).await?;
    info!("listening on {}", addr);
    axum::serve(listener, app.into_make_service()).await?;
    Ok(())
}

#[instrument]
async fn index_handler() -> &'static str {
    debug!("index handler started");
    sleep(Duration::from_millis(10)).await;
    let ret = long_task().await;
    info!(http.status = 200, "index handler completed");
    ret
}

#[instrument]
async fn long_task() -> &'static str {
    let start = Instant::now();
    sleep(Duration::from_millis(112)).await;
    let elapsed = start.elapsed().as_millis() as u64;
    warn!(app.task_duration = elapsed, "long task done");
    "long task done"
}

第四次运行

查看日志

实时查看日志

tail -f 是一个在 Linux/Unix 系统中常用的命令，用于实时查看文件的末尾内容。它可以在文件被追加内容时，实时显示这些内容，而不需要重新加载整个文件。

总结

通过本文的实战演练，我们从简单的日志输出开始，逐步优化到支持耗时统计和文件记录，展示了 tracing 生态的强大功能。无论是调试还是生产环境，合理配置日志都能提升开发效率和系统可观测性。希望这篇文章能为你的 Rust 项目提供实用参考，助你在日志处理上更进一步！

参考

• https://github.com/tokio-rs/tracing
• https://course.rs/logs/tracing.html
• https://crates.io/crates/tracing-subscriber
• https://docs.rs/tracing-subscriber/latest/tracing_subscriber/index.html
• https://docs.rs/tracing-subscriber/latest/tracing_subscriber/layer/index.html
• https://github.com/tokio-rs/tracing/tree/master/tracing-appender