feat(sampler): allow configuring excluded URL paths for tracing (#36)

Author: maoanran

README.md

@@ -0,0 +1,15 @@
+# OpenTelemetry Extension
+
+This is an OpenTelemetry SDK extension that provides custom sampling and resource configuration. The extension automatically configures OpenTelemetry instrumentation with environment-specific settings and intelligent sampling rules.
+
+## Configuration
+
+The extension can be configured using the following environment variables:
+
+| Environment Variable             | Description                                                                                                                               |
+|----------------------------------| ----------------------------------------------------------------------------------------------------------------------------------------- |
+| `SERVICE_NAME`                   | The name of the service.                                                                                                                  |
+| `STAGE`                          | The deployment stage (e.g., `production`, `staging`).                                                                                     |
+| `BUILD_NUMBER`                   | The build number of the service.                                                                                                          |
+| `OTEL_TRACES_SAMPLER_ARG`        | The sampling rate to use. Overrides the default sampling rate.                                                                            |
+| `OTEL_TRACES_EXCLUDED_URL_PATHS` | A comma-separated list of URL paths to exclude from tracing (e.g., `/health*,/metrics*`). Defaults to `/health*,/prometheus*,/metrics*`. |

src/main/kotlin/com/monta/otel/extension/Customizer.java

@@ -2,14 +2,18 @@
 
 import io.opentelemetry.api.trace.SpanKind;
 import io.opentelemetry.contrib.sampler.RuleBasedRoutingSampler;
+import io.opentelemetry.contrib.sampler.RuleBasedRoutingSamplerBuilder;
 import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizer;
 import io.opentelemetry.sdk.autoconfigure.spi.AutoConfigurationCustomizerProvider;
 import io.opentelemetry.sdk.resources.Resource;
+import io.opentelemetry.sdk.trace.SdkTracerProviderBuilder;
 import io.opentelemetry.sdk.trace.samplers.Sampler;
 import io.opentelemetry.semconv.ServiceAttributes;
 import io.opentelemetry.semconv.UrlAttributes;
 
+import java.util.Arrays;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.UUID;
 
 /**
@@ -18,6 +22,9 @@
  */
 public class Customizer implements AutoConfigurationCustomizerProvider {
 
+    private static final String OTEL_TRACES_EXCLUDED_URL_PATHS_ENV_VAR = "OTEL_TRACES_EXCLUDED_URL_PATHS";
+    private static final String DEFAULT_EXCLUDED_URL_PATHS = "/health*,/prometheus*,/metrics*";
+
     @Override
     public void customize(AutoConfigurationCustomizer autoConfiguration) {
 
@@ -33,21 +40,28 @@ public void customize(AutoConfigurationCustomizer autoConfiguration) {
                 )
         );
 
-        // Set the sampler to be the default parentbased_always_on, but drop calls to spring
-        // boot actuator endpoints
-        autoConfiguration.addTracerProviderCustomizer((sdkTracerProviderBuilder, configProperties) ->
-                sdkTracerProviderBuilder.setSampler(
-                        Sampler.parentBased(
-                                RuleBasedRoutingSampler.builder(SpanKind.SERVER, getSampler())
-                                        .drop(UrlAttributes.URL_PATH, "/health*")
-                                        .drop(UrlAttributes.URL_PATH, "/prometheus*")
-                                        .drop(UrlAttributes.URL_PATH, "/metrics*")
-                                        .build()
-                        )
-                )
+        autoConfiguration.addTracerProviderCustomizer((builder, config) ->
+                configureSampler(builder)
         );
     }
 
+    /**
+     * Configures the SdkTracerProviderBuilder with a rule-based routing sampler.
+     */
+    private SdkTracerProviderBuilder configureSampler(SdkTracerProviderBuilder builder) {
+        RuleBasedRoutingSamplerBuilder samplerBuilder = RuleBasedRoutingSampler.builder(SpanKind.SERVER, getSampler());
+
+        String excludedPaths = Optional.ofNullable(System.getenv(OTEL_TRACES_EXCLUDED_URL_PATHS_ENV_VAR))
+                .orElse(DEFAULT_EXCLUDED_URL_PATHS);
+
+        Arrays.stream(excludedPaths.split(","))
+                .map(String::trim)
+                .filter(path -> !path.isEmpty())
+                .forEach(path -> samplerBuilder.drop(UrlAttributes.URL_PATH, path));
+
+        return builder.setSampler(Sampler.parentBased(samplerBuilder.build()));
+    }
+
     private static Sampler getSampler() {
 
         String otelTracesSamplerArg = System.getenv("OTEL_TRACES_SAMPLER_ARG");