Allow setting the OTLP tracing sample rate

Author: sandhose

crates/cli/src/telemetry.rs

@@ -102,7 +102,10 @@ fn stdout_tracer_provider() -> SdkTracerProvider {
         .build()
 }
 
-fn otlp_tracer_provider(endpoint: Option<&Url>) -> anyhow::Result<SdkTracerProvider> {
+fn otlp_tracer_provider(
+    endpoint: Option<&Url>,
+    sample_rate: f64,
+) -> anyhow::Result<SdkTracerProvider> {
     let mut exporter = opentelemetry_otlp::SpanExporter::builder()
         .with_http()
         .with_http_client(mas_http::reqwest_client());
@@ -119,17 +122,18 @@ fn otlp_tracer_provider(endpoint: Option<&Url>) -> anyhow::Result<SdkTracerProvi
     let tracer_provider = SdkTracerProvider::builder()
         .with_span_processor(batch_processor)
         .with_resource(resource())
-        .with_sampler(Sampler::AlwaysOn)
+        .with_sampler(Sampler::TraceIdRatioBased(sample_rate))
         .build();
 
     Ok(tracer_provider)
 }
 
 fn init_tracer(config: &TracingConfig) -> anyhow::Result<()> {
+    let sample_rate = config.sample_rate.unwrap_or(1.0);
     let tracer_provider = match config.exporter {
         TracingExporterKind::None => return Ok(()),
         TracingExporterKind::Stdout => stdout_tracer_provider(),
-        TracingExporterKind::Otlp => otlp_tracer_provider(config.endpoint.as_ref())?,
+        TracingExporterKind::Otlp => otlp_tracer_provider(config.endpoint.as_ref(), sample_rate)?,
     };
     TRACER_PROVIDER
         .set(tracer_provider.clone())

crates/config/src/sections/telemetry.rs

@@ -65,6 +65,13 @@ pub struct TracingConfig {
     /// List of propagation formats to use for incoming and outgoing requests
     #[serde(default)]
     pub propagators: Vec<Propagator>,
+
+    /// Sample rate for traces
+    ///
+    /// Defaults to `1.0` if not set.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    #[schemars(example = "sample_rate_example", range(min = 0.0, max = 1.0))]
+    pub sample_rate: Option<f64>,
 }
 
 impl TracingConfig {

docs/config.schema.json

@@ -1213,6 +1213,16 @@
           "items": {
             "$ref": "#/definitions/Propagator"
           }
+        },
+        "sample_rate": {
+          "description": "Sample rate for traces\n\nDefaults to `1.0` if not set.",
+          "examples": [
+            0.5
+          ],
+          "type": "number",
+          "format": "double",
+          "maximum": 1.0,
+          "minimum": 0.0
         }
       }
     },