Why don't I get traces when sending OpenTelemetry to Jaeger?

Question

I'm learning tracing and open-telemetry in Rust. I feel there are too many concepts and too many crates (at least in Rust) to see traces.

I wrote a simple lib app that adds two u32s:

use std::ops::Add;

pub fn add(f: u32, s: u32) -> u32 {
    let span = tracing::info_span!("Add function", ?f, ?s);
    let _guard = span.enter();
    tracing::info!("Info event");
    f.add(s)
}

And then I'm using the lib in my binary app:

use TracedLibrary::add;
use tracing_opentelemetry::OpenTelemetryLayer;
use tracing_subscriber::util::SubscriberInitExt;
use opentelemetry::{global, sdk::propagation::TraceContextPropagator};
use tracing_subscriber::layer::SubscriberExt;
use tracing_subscriber::Registry;

fn main() {
    setup_global_subscriber();
    let sum = add::add(1, 2);
}

fn setup_global_subscriber() {
    global::set_text_map_propagator(TraceContextPropagator::new());
    let (tracer, _uninstall) = opentelemetry_jaeger::new_pipeline()
        .with_service_name("trace_demo_2")
        .install().expect("Error initializing Jaeger exporter");
    let telemetry = tracing_opentelemetry::layer().with_tracer(tracer);

    Registry::default()
        .with(telemetry).init();
}

The most confusing part is my apps Cargo.toml which looks like

tracing-subscriber = { version = "0.2.15" }
tracing-opentelemetry = { version= "0.11.0"}
opentelemetry = "0.12.0"
opentelemetry-jaeger = {version = "0.11.0" }

What on earth are those different crates are for? The only crate that makes sense is opentelemetry-jaeger. Are others even required?

And to my main question: I'm running Jaeger's all-in-one docker container. But when I visit http://localhost:16686, I see no traces. Does anyone know what's happening?

Answer 1

Turns out when I create the Jaeger pipeline in setup_global_subscriber(), the _uninstall being returned gets dropped at the end of the function. And when it gets dropped, collector shuts down.

To get traces I had to move contents of setup_global_subscriber() in main().

Answer 2

I think this is what you need.

    tracing::subscriber::set_global_default(subscriber);

This sets a global Dispatcher, which Dispatcher.inner is your subscriber.