swarm-notify-router: export event, todo, review request and consumer metrics

swarm-secret-client/src/lib.rs

@@ -45,6 +45,8 @@ pub mod github;
 pub mod gitlab;
 pub mod grafana;
 pub mod matrix;
+#[cfg(feature = "otel")]
+pub mod meter_provider;
 pub mod mtls;
 pub mod observability;
 pub mod path;

swarm-secret-client/src/meter_provider.rs

@@ -0,0 +1,47 @@
+//! The meter provider a swarm service pushes its OTLP metrics through.
+//!
+//! Built from the standard `OTEL_*` environment: the endpoint from
+//! `OTEL_EXPORTER_OTLP_ENDPOINT` and the resource from
+//! `OTEL_RESOURCE_ATTRIBUTES`. With no endpoint a service exports nothing, so
+//! a run outside the swarm (a test, a dev shell) needs no collector.
+
+use std::time::Duration;
+
+use opentelemetry_otlp::{MetricExporter, Protocol, WithExportConfig};
+use opentelemetry_sdk::metrics::{PeriodicReader, SdkMeterProvider};
+
+/// How often the metrics are exported.
+const INTERVAL: Duration = Duration::from_mins(1);
+
+/// The provider for the service `cert` names in the `bao.client_cert.*` gauges
+/// it also registers on a meter called `meter`, or `None` when no collector is
+/// configured or the exporter failed to build.
+///
+/// The caller keeps the provider alive: it exports only while it lives.
+#[must_use]
+pub fn from_env(meter: &'static str, cert: &'static str) -> Option<SdkMeterProvider> {
+    use opentelemetry::metrics::MeterProvider as _;
+
+    if !std::env::var("OTEL_EXPORTER_OTLP_ENDPOINT").is_ok_and(|s| !s.trim().is_empty()) {
+        return None;
+    }
+    // The blocking client: `PeriodicReader` exports from a thread of its own
+    // with no Tokio reactor.
+    let exporter = match MetricExporter::builder()
+        .with_http()
+        .with_protocol(Protocol::HttpJson)
+        .build()
+    {
+        Ok(exporter) => exporter,
+        Err(e) => {
+            tracing::warn!(error = %e, meter, "building the metric exporter failed; no metrics are exported");
+            return None;
+        }
+    };
+    let reader = PeriodicReader::builder(exporter)
+        .with_interval(INTERVAL)
+        .build();
+    let provider = SdkMeterProvider::builder().with_reader(reader).build();
+    crate::cert_metrics::register(&provider.meter(meter), cert);
+    Some(provider)
+}