Move all the OTEL meters to crate-level statics

crates/cli/src/app_state.rs

@@ -29,6 +29,8 @@ use opentelemetry::{metrics::Histogram, KeyValue};
 use rand::SeedableRng;
 use sqlx::PgPool;
 
+use crate::telemetry::METER;
+
 #[derive(Clone)]
 pub struct AppState {
     pub pool: PgPool,
@@ -53,15 +55,8 @@ pub struct AppState {
 impl AppState {
     /// Init the metrics for the app state.
     pub fn init_metrics(&mut self) {
-        // XXX: do we want to put that somewhere else?
-        let scope = opentelemetry::InstrumentationScope::builder(env!("CARGO_PKG_NAME"))
-            .with_version(env!("CARGO_PKG_VERSION"))
-            .with_schema_url(opentelemetry_semantic_conventions::SCHEMA_URL)
-            .build();
-        let meter = opentelemetry::global::meter_with_scope(scope);
-
         let pool = self.pool.clone();
-        meter
+        METER
             .i64_observable_up_down_counter("db.connections.usage")
             .with_description("The number of connections that are currently in `state` described by the state attribute.")
             .with_unit("{connection}")
@@ -74,7 +69,7 @@ impl AppState {
             .build();
 
         let pool = self.pool.clone();
-        meter
+        METER
             .i64_observable_up_down_counter("db.connections.max")
             .with_description("The maximum number of open connections allowed.")
             .with_unit("{connection}")
@@ -85,7 +80,7 @@ impl AppState {
             .build();
 
         // Track the connection acquisition time
-        let histogram = meter
+        let histogram = METER
             .u64_histogram("db.client.connections.create_time")
             .with_description("The time it took to create a new connection.")
             .with_unit("ms")

crates/cli/src/main.rs

@@ -119,11 +119,11 @@ async fn try_main() -> anyhow::Result<ExitCode> {
     });
 
     // Setup OpenTelemetry tracing and metrics
-    let tracer = telemetry::setup(&telemetry_config).context("failed to setup OpenTelemetry")?;
+    self::telemetry::setup(&telemetry_config).context("failed to setup OpenTelemetry")?;
 
-    let telemetry_layer = tracer.map(|tracer| {
+    let telemetry_layer = self::telemetry::TRACER.get().map(|tracer| {
         tracing_opentelemetry::layer()
-            .with_tracer(tracer)
+            .with_tracer(tracer.clone())
             .with_tracked_inactivity(false)
             .with_filter(LevelFilter::INFO)
     });

crates/cli/src/telemetry.rs

@@ -4,7 +4,10 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 // Please see LICENSE in the repository root for full details.
 
-use std::time::Duration;
+use std::{
+    sync::{LazyLock, OnceLock},
+    time::Duration,
+};
 
 use anyhow::Context as _;
 use bytes::Bytes;
@@ -15,7 +18,7 @@ use mas_config::{
     TracingExporterKind,
 };
 use opentelemetry::{
-    global,
+    metrics::Meter,
     propagation::{TextMapCompositePropagator, TextMapPropagator},
     trace::TracerProvider as _,
     InstrumentationScope, KeyValue,
@@ -23,7 +26,6 @@ use opentelemetry::{
 use opentelemetry_otlp::{WithExportConfig, WithHttpConfig};
 use opentelemetry_prometheus::PrometheusExporter;
 use opentelemetry_sdk::{
-    self,
     metrics::{ManualReader, PeriodicReader, SdkMeterProvider},
     propagation::{BaggagePropagator, TraceContextPropagator},
     trace::{Sampler, Tracer, TracerProvider},
@@ -31,29 +33,38 @@ use opentelemetry_sdk::{
 };
 use opentelemetry_semantic_conventions as semcov;
 use prometheus::Registry;
-use tokio::sync::OnceCell;
 use url::Url;
 
-static METER_PROVIDER: OnceCell<SdkMeterProvider> = OnceCell::const_new();
-static PROMETHEUS_REGISTRY: OnceCell<Registry> = OnceCell::const_new();
+static SCOPE: LazyLock<InstrumentationScope> = LazyLock::new(|| {
+    InstrumentationScope::builder(env!("CARGO_PKG_NAME"))
+        .with_version(env!("CARGO_PKG_VERSION"))
+        .with_schema_url(semcov::SCHEMA_URL)
+        .build()
+});
 
-pub fn setup(config: &TelemetryConfig) -> anyhow::Result<Option<Tracer>> {
+pub static METER: LazyLock<Meter> =
+    LazyLock::new(|| opentelemetry::global::meter_with_scope(SCOPE.clone()));
+
+pub static TRACER: OnceLock<Tracer> = OnceLock::new();
+static METER_PROVIDER: OnceLock<SdkMeterProvider> = OnceLock::new();
+static PROMETHEUS_REGISTRY: OnceLock<Registry> = OnceLock::new();
+
+pub fn setup(config: &TelemetryConfig) -> anyhow::Result<()> {
     let propagator = propagator(&config.tracing.propagators);
 
     // The CORS filter needs to know what headers it should whitelist for
     // CORS-protected requests.
     mas_http::set_propagator(&propagator);
-    global::set_text_map_propagator(propagator);
-
-    let tracer = tracer(&config.tracing).context("Failed to configure traces exporter")?;
+    opentelemetry::global::set_text_map_propagator(propagator);
 
+    init_tracer(&config.tracing).context("Failed to configure traces exporter")?;
     init_meter(&config.metrics).context("Failed to configure metrics exporter")?;
 
-    Ok(tracer)
+    Ok(())
 }
 
 pub fn shutdown() {
-    global::shutdown_tracer_provider();
+    opentelemetry::global::shutdown_tracer_provider();
 
     if let Some(meter_provider) = METER_PROVIDER.get() {
         meter_provider.shutdown().unwrap();
@@ -93,32 +104,30 @@ fn otlp_tracer_provider(endpoint: Option<&Url>) -> anyhow::Result<TracerProvider
         .build()
         .context("Failed to configure OTLP trace exporter")?;
 
-    let tracer = opentelemetry_sdk::trace::TracerProvider::builder()
+    let tracer_provider = opentelemetry_sdk::trace::TracerProvider::builder()
         .with_batch_exporter(exporter, opentelemetry_sdk::runtime::Tokio)
         .with_resource(resource())
         .with_sampler(Sampler::AlwaysOn)
         .build();
 
-    Ok(tracer)
+    Ok(tracer_provider)
 }
 
-fn tracer(config: &TracingConfig) -> anyhow::Result<Option<Tracer>> {
+fn init_tracer(config: &TracingConfig) -> anyhow::Result<()> {
     let tracer_provider = match config.exporter {
-        TracingExporterKind::None => return Ok(None),
+        TracingExporterKind::None => return Ok(()),
         TracingExporterKind::Stdout => stdout_tracer_provider(),
         TracingExporterKind::Otlp => otlp_tracer_provider(config.endpoint.as_ref())?,
     };
 
-    let scope = InstrumentationScope::builder(env!("CARGO_PKG_NAME"))
-        .with_version(env!("CARGO_PKG_VERSION"))
-        .with_schema_url(semcov::SCHEMA_URL)
-        .build();
+    let tracer = tracer_provider.tracer_with_scope(SCOPE.clone());
+    TRACER
+        .set(tracer)
+        .map_err(|_| anyhow::anyhow!("TRACER was set twice"))?;
 
-    let tracer = tracer_provider.tracer_with_scope(scope);
+    opentelemetry::global::set_tracer_provider(tracer_provider);
 
-    global::set_tracer_provider(tracer_provider);
-
-    Ok(Some(tracer))
+    Ok(())
 }
 
 fn otlp_metric_reader(endpoint: Option<&url::Url>) -> anyhow::Result<PeriodicReader> {
@@ -175,7 +184,7 @@ fn prometheus_service_fn<T>(_req: T) -> PromServiceFuture {
 }
 
 pub fn prometheus_service<T>() -> tower::util::ServiceFn<fn(T) -> PromServiceFuture> {
-    if !PROMETHEUS_REGISTRY.initialized() {
+    if PROMETHEUS_REGISTRY.get().is_none() {
         tracing::warn!("A Prometheus resource was mounted on a listener, but the Prometheus exporter was not setup in the config");
     }
 
@@ -184,7 +193,10 @@ pub fn prometheus_service<T>() -> tower::util::ServiceFn<fn(T) -> PromServiceFut
 
 fn prometheus_metric_reader() -> anyhow::Result<PrometheusExporter> {
     let registry = Registry::new();
-    PROMETHEUS_REGISTRY.set(registry.clone())?;
+
+    PROMETHEUS_REGISTRY
+        .set(registry.clone())
+        .map_err(|_| anyhow::anyhow!("PROMETHEUS_REGISTRY was set twice"))?;
 
     let exporter = opentelemetry_prometheus::exporter()
         .with_registry(registry)
@@ -209,8 +221,10 @@ fn init_meter(config: &MetricsConfig) -> anyhow::Result<()> {
 
     let meter_provider = meter_provider_builder.with_resource(resource()).build();
 
-    METER_PROVIDER.set(meter_provider.clone())?;
-    global::set_meter_provider(meter_provider.clone());
+    METER_PROVIDER
+        .set(meter_provider.clone())
+        .map_err(|_| anyhow::anyhow!("METER_PROVIDER was set twice"))?;
+    opentelemetry::global::set_meter_provider(meter_provider.clone());
 
     Ok(())
 }

crates/handlers/src/activity_tracker/worker.rs

@@ -16,7 +16,10 @@ use sqlx::PgPool;
 use tokio_util::sync::CancellationToken;
 use ulid::Ulid;
 
-use crate::activity_tracker::{Message, SessionKind};
+use crate::{
+    activity_tracker::{Message, SessionKind},
+    METER,
+};
 
 /// The maximum number of pending activity records before we flush them to the
 /// database automatically.
@@ -48,13 +51,7 @@ pub struct Worker {
 
 impl Worker {
     pub(crate) fn new(pool: PgPool) -> Self {
-        let scope = opentelemetry::InstrumentationScope::builder(env!("CARGO_PKG_NAME"))
-            .with_version(env!("CARGO_PKG_VERSION"))
-            .with_schema_url(opentelemetry_semantic_conventions::SCHEMA_URL)
-            .build();
-        let meter = opentelemetry::global::meter_with_scope(scope);
-
-        let message_counter = meter
+        let message_counter = METER
             .u64_counter("mas.activity_tracker.messages")
             .with_description("The number of messages received by the activity tracker")
             .with_unit("{messages}")
@@ -77,7 +74,7 @@ impl Worker {
         message_counter.add(0, &[KeyValue::new(TYPE, "flush")]);
         message_counter.add(0, &[KeyValue::new(TYPE, "shutdown")]);
 
-        let flush_time_histogram = meter
+        let flush_time_histogram = METER
             .u64_histogram("mas.activity_tracker.flush_time")
             .with_description("The time it took to flush the activity tracker")
             .with_unit("ms")

crates/handlers/src/lib.rs

@@ -15,7 +15,7 @@
     clippy::let_with_type_underscore,
 )]
 
-use std::{convert::Infallible, time::Duration};
+use std::{convert::Infallible, sync::LazyLock, time::Duration};
 
 use axum::{
     extract::{FromRef, FromRequestParts, OriginalUri, RawQuery, State},
@@ -41,6 +41,7 @@ use mas_policy::Policy;
 use mas_router::{Route, UrlBuilder};
 use mas_storage::{BoxClock, BoxRepository, BoxRng};
 use mas_templates::{ErrorContext, NotFoundContext, TemplateContext, Templates};
+use opentelemetry::metrics::Meter;
 use passwords::PasswordManager;
 use sqlx::PgPool;
 use tower::util::AndThenLayer;
@@ -62,6 +63,15 @@ mod rate_limit;
 #[cfg(test)]
 mod test_utils;
 
+static METER: LazyLock<Meter> = LazyLock::new(|| {
+    let scope = opentelemetry::InstrumentationScope::builder(env!("CARGO_PKG_NAME"))
+        .with_version(env!("CARGO_PKG_VERSION"))
+        .with_schema_url(opentelemetry_semantic_conventions::SCHEMA_URL)
+        .build();
+
+    opentelemetry::global::meter_with_scope(scope)
+});
+
 /// Implement `From<E>` for `RouteError`, for "internal server error" kind of
 /// errors.
 #[macro_export]

crates/tower/src/lib.rs

@@ -6,6 +6,10 @@
 
 #![allow(clippy::module_name_repetitions)]
 
+use std::sync::LazyLock;
+
+use opentelemetry::metrics::Meter;
+
 mod metrics;
 mod trace_context;
 mod tracing;
@@ -13,11 +17,11 @@ mod utils;
 
 pub use self::{metrics::*, trace_context::*, tracing::*, utils::*};
 
-fn meter() -> opentelemetry::metrics::Meter {
+static METER: LazyLock<Meter> = LazyLock::new(|| {
     let scope = opentelemetry::InstrumentationScope::builder(env!("CARGO_PKG_NAME"))
         .with_version(env!("CARGO_PKG_VERSION"))
         .with_schema_url(opentelemetry_semantic_conventions::SCHEMA_URL)
         .build();
 
     opentelemetry::global::meter_with_scope(scope)
-}
+});

crates/tower/src/metrics/duration.rs

@@ -10,7 +10,7 @@ use opentelemetry::{metrics::Histogram, KeyValue};
 use pin_project_lite::pin_project;
 use tower::{Layer, Service};
 
-use crate::{utils::FnWrapper, MetricsAttributes};
+use crate::{utils::FnWrapper, MetricsAttributes, METER};
 
 /// A [`Layer`] that records the duration of requests in milliseconds.
 #[derive(Clone, Debug)]
@@ -25,7 +25,7 @@ impl DurationRecorderLayer {
     /// Create a new [`DurationRecorderLayer`].
     #[must_use]
     pub fn new(name: &'static str) -> Self {
-        let histogram = crate::meter().u64_histogram(name).build();
+        let histogram = METER.u64_histogram(name).build();
         Self {
             histogram,
             on_request: (),

crates/tower/src/metrics/in_flight.rs

@@ -10,7 +10,7 @@ use opentelemetry::{metrics::UpDownCounter, KeyValue};
 use pin_project_lite::pin_project;
 use tower::{Layer, Service};
 
-use crate::MetricsAttributes;
+use crate::{MetricsAttributes, METER};
 
 /// A [`Layer`] that records the number of in-flight requests.
 ///
@@ -27,7 +27,7 @@ impl InFlightCounterLayer {
     /// Create a new [`InFlightCounterLayer`].
     #[must_use]
     pub fn new(name: &'static str) -> Self {
-        let counter = crate::meter()
+        let counter = METER
             .i64_up_down_counter(name)
             .with_unit("{request}")
             .with_description("The number of in-flight requests")