Axum and tracing to a file

[kellytk]

[referred from tokio-rs/axum#752 (comment)]

I have an Axum-based project successfully tracing to a file with one exception, request tracing.

I've followed the tracing-aka-logging example to make https://github.com/kellytk/axum-trace. The code runs as expected tracing to the terminal, however if I comment out this line and uncomment the following line, request handling traces do not appear in the file.

How please should it be correctly configured?

[hawkw]

One thing I noticed is that in your code for configuring tracing, you are configuring your fmt subscriber to filter spans and events based on a max level (DEBUG): https://github.com/kellytk/axum-trace/blob/b3f4018fa3a44bf0c49c24ba78fbed3df217570b/src/main.rs#L33. However, when you just call tracing_subscriber::fmt::init, it defaults to using an EnvFilter configured from the RUST_LOG environment variable. I notice that you are setting a value for this environment variable here if it is unset. However, in your tracer() function, that environment variable will not be used.

Try changing the call to with_max_level(...) to

// ...
   .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
   // ...

You may need to enable the "env-filter" feature flag of the tracing-subscriber crate, if it is not already enabled.

[kellytk]

Thank you @hawkw. I've made the change you suggested with no difference in behavior. The "listening on..." event is traced to file however request traces are not. I have confirmed the presence of the env-filter feature flag. If you have further ideas I'd appreciate it.

The level overlap is from mixing the example's code into my own.

[hawkw]

Which specific traces do you see when using fmt::init() but not when logging to the file? Can you share the output in both cases or something?

[kellytk]

@hawkw I've added the output of each at https://github.com/kellytk/axum-trace. I've also pushed your prior suggestion.