make edot sampler default instead of forcing it on (#841)

* Make edot sampler default but not forced

* Fix

* Warn when dynamic sampler wasn't initialized

* Check actual sampler in agent listener

* Fix

* Cleanup

Author: anuraaga

custom/src/main/java/co/elastic/otel/ElasticAutoConfigurationCustomizerProvider.java

@@ -18,7 +18,6 @@
  */
 package co.elastic.otel;
 
-import co.elastic.otel.compositesampling.DynamicCompositeParentBasedTraceIdRatioBasedSampler;
 import co.elastic.otel.config.ConfigLoggingAgentListener;
 import co.elastic.otel.dynamicconfig.BlockableLogRecordExporter;
 import co.elastic.otel.dynamicconfig.BlockableMetricExporter;
@@ -46,6 +45,7 @@ public class ElasticAutoConfigurationCustomizerProvider
       "otel.instrumentation.runtime-telemetry.emit-experimental-telemetry";
   private static final String METRIC_TEMPORALITY_PREFERENCE =
       "otel.exporter.otlp.metrics.temporality.preference";
+  private static final String TRACES_SAMPLER = "otel.traces.sampler";
 
   // must match value in io.opentelemetry.contrib.stacktrace.StackTraceAutoConfig
   private static final String STACKTRACE_OTEL_FILTER =
@@ -93,7 +93,6 @@ public void customize(AutoConfigurationCustomizer autoConfiguration) {
         (providerBuilder, properties) -> {
           CentralConfig.init(providerBuilder, properties);
           AgentLog.addSpanLoggingIfRequired(providerBuilder, properties);
-          providerBuilder.setSampler(DynamicCompositeParentBasedTraceIdRatioBasedSampler.INSTANCE);
           return providerBuilder;
         });
   }
@@ -105,6 +104,7 @@ static Map<String, String> propertiesCustomizer(ConfigProperties configPropertie
     deltaMetricsTemporality(config, configProperties);
     resourceProviders(config, configProperties);
     spanStackTrace(config, configProperties);
+    defaultSampler(config, configProperties);
     ConfigLoggingAgentListener.logTheConfig(
         configProperties.getBoolean(ConfigLoggingAgentListener.LOG_THE_CONFIG, true));
 
@@ -151,6 +151,15 @@ private static void resourceProviders(
     config.put(DISABLED_RESOURCE_PROVIDERS, String.join(",", disabledResourceProviders));
   }
 
+  private static void defaultSampler(
+      Map<String, String> config, ConfigProperties configProperties) {
+    // enable EDOT default sampler by default if not explicitly disabled
+    String sampler =
+        configProperties.getString(
+            TRACES_SAMPLER, "experimental_composite_parentbased_traceidratio");
+    config.put(TRACES_SAMPLER, sampler);
+  }
+
   private static void spanStackTrace(
       Map<String, String> config, ConfigProperties configProperties) {
 

custom/src/main/java/co/elastic/otel/config/ConfigLoggingAgentListener.java

@@ -18,6 +18,7 @@
  */
 package co.elastic.otel.config;
 
+import co.elastic.otel.compositesampling.DynamicCompositeParentBasedTraceIdRatioBasedSampler;
 import com.google.auto.service.AutoService;
 import io.opentelemetry.javaagent.extension.AgentListener;
 import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk;
@@ -27,6 +28,9 @@
 public class ConfigLoggingAgentListener implements AgentListener {
   public static final String LOG_THE_CONFIG =
       "elastic.otel.java.experimental.configuration.logging.enabled";
+
+  private static volatile boolean enableDynamicSamplingRate = false;
+
   private static final Logger logger = Logger.getLogger(ConfigLoggingAgentListener.class.getName());
 
   private static boolean logTheConfig = true;
@@ -35,11 +39,19 @@ public static synchronized void logTheConfig(boolean logTheConfig) {
     ConfigLoggingAgentListener.logTheConfig = logTheConfig;
   }
 
+  public static boolean getEnableDynamicSamplingRate() {
+    return enableDynamicSamplingRate;
+  }
+
   @Override
   public void afterAgent(AutoConfiguredOpenTelemetrySdk autoConfiguredOpenTelemetrySdk) {
     if (logTheConfig) {
       logger.info(autoConfiguredOpenTelemetrySdk.toString());
     }
+    if (autoConfiguredOpenTelemetrySdk.getOpenTelemetrySdk().getSdkTracerProvider().getSampler()
+        instanceof DynamicCompositeParentBasedTraceIdRatioBasedSampler) {
+      enableDynamicSamplingRate = true;
+    }
   }
 
   @Override

custom/src/main/java/co/elastic/otel/dynamicconfig/CentralConfig.java

@@ -19,6 +19,7 @@
 package co.elastic.otel.dynamicconfig;
 
 import co.elastic.otel.compositesampling.DynamicCompositeParentBasedTraceIdRatioBasedSampler;
+import co.elastic.otel.config.ConfigLoggingAgentListener;
 import co.elastic.otel.dynamicconfig.internal.OpampManager;
 import co.elastic.otel.logging.AgentLog;
 import io.opentelemetry.contrib.inferredspans.InferredSpans;
@@ -329,6 +330,10 @@ public static final class SamplingRate extends ConfigOption {
     @Override
     void update(String configurationValue, OpampManager opampManager)
         throws IllegalArgumentException {
+      if (!ConfigLoggingAgentListener.getEnableDynamicSamplingRate()) {
+        logger.warning("ignoring \"sampling_rate\" because non-default sampler in use");
+        return;
+      }
       DynamicCompositeParentBasedTraceIdRatioBasedSampler.setRatio(
           Double.parseDouble(configurationValue));
     }

custom/src/test/java/co/elastic/otel/ElasticAutoConfigurationCustomizerProviderTest.java

@@ -52,6 +52,10 @@ void defaultConfiguration() {
         .describedAs("runtime experimental metrics must be enabled")
         .containsEntry(
             "otel.instrumentation.runtime-telemetry.emit-experimental-telemetry", "true");
+
+    assertThat(config)
+        .describedAs("edot default sampler when not set by user")
+        .containsEntry("otel.traces.sampler", "experimental_composite_parentbased_traceidratio");
   }
 
   @Test
@@ -98,6 +102,16 @@ void customizeMetricTemporalityPreference() {
     assertThat(value).isEqualTo("LOWMEMORY");
   }
 
+  @Test
+  void customizeSampler() {
+    Map<String, String> userConfig = new HashMap<>();
+    userConfig.put("otel.traces.sampler", "always_off");
+    Map<String, String> config =
+        propertiesCustomizer(DefaultConfigProperties.createFromMap(userConfig));
+    String value = config.get("otel.traces.sampler");
+    assertThat(value).isEqualTo("always_off");
+  }
+
   @Test
   void verifyDefaultTemporalityOverriddenToDelta() {
     try (OpenTelemetrySdk sdk =