zero-to-production/src/telemetry.rs

use tracing::subscriber::set_global_default;
use tracing::Subscriber;
use tracing_bunyan_formatter::{BunyanFormattingLayer, JsonStorageLayer};
use tracing_log::LogTracer;
use tracing_subscriber::fmt::MakeWriter;
use tracing_subscriber::{layer::SubscriberExt, EnvFilter, Registry};

/// Compose multiple layers into a `tracing`'s subscriber.
///
/// # Implementation Notes
///
/// We are using `impl Subscriber` as return type to avoid having to spell out the actual
/// type of the returned subscriber, which is indeed quite complex.
pub fn get_subscriber<Sink>(
    name: String,
    env_filter: String,
    sink: Sink,
) -> impl Subscriber + Sync + Send
where
    Sink: for<'a> MakeWriter<'a> + Send + Sync + 'static,
{
    let env_filter =
        EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new(env_filter));
    let formatting_layer = BunyanFormattingLayer::new(name, sink);
    Registry::default()
        .with(env_filter)
        .with(JsonStorageLayer)
        .with(formatting_layer)
}

/// Register a subscriber as global default to process span data.
///
/// It should only be called once!
pub fn init_subscriber(subscriber: impl Subscriber + Sync + Send) {
    LogTracer::init().expect("Failed to set logger");
    set_global_default(subscriber).expect("Failed to set subscriber");
}