SOLR-16938 Auto configure tracer without a <tracerConfig> tag in solr…

solr/core/src/java/org/apache/solr/core/TracerConfigurator.java

@@ -18,29 +18,78 @@
 package org.apache.solr.core;
 
 import io.opentelemetry.api.trace.Tracer;
+import java.lang.invoke.MethodHandles;
+import java.util.Locale;
+import org.apache.solr.common.SolrException;
+import org.apache.solr.common.util.NamedList;
 import org.apache.solr.util.plugin.NamedListInitializedPlugin;
 import org.apache.solr.util.tracing.SimplePropagator;
 import org.apache.solr.util.tracing.TraceUtils;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 /** Produces a {@link Tracer} from configuration. */
 public abstract class TracerConfigurator implements NamedListInitializedPlugin {
 
   public static final boolean TRACE_ID_GEN_ENABLED =
       Boolean.parseBoolean(System.getProperty("solr.alwaysOnTraceId", "true"));
 
+  private static final String DEFAULT_CLASS_NAME =
+      System.getProperty(
+          "solr.otelDefaultConfigurator", "org.apache.solr.opentelemetry.OtelTracerConfigurator");
+
+  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+
   public static Tracer loadTracer(SolrResourceLoader loader, PluginInfo info) {
     if (info != null && info.isEnabled()) {
       TracerConfigurator configurator =
           loader.newInstance(info.className, TracerConfigurator.class);
       configurator.init(info.initArgs);
       return configurator.getTracer();
-
-    } else if (TRACE_ID_GEN_ENABLED) {
+    }
+    if (shouldAutoConfigOTEL()) {
+      return autoConfigOTEL(loader);
+    }
+    if (TRACE_ID_GEN_ENABLED) {
       return SimplePropagator.load();
-    } else {
-      return TraceUtils.noop();
     }
+    return TraceUtils.getGlobalTracer();
   }
 
   protected abstract Tracer getTracer();
+
+  private static Tracer autoConfigOTEL(SolrResourceLoader loader) {
+    try {
+      TracerConfigurator configurator =
+          loader.newInstance(DEFAULT_CLASS_NAME, TracerConfigurator.class);
+      configurator.init(new NamedList<>());
+      return configurator.getTracer();
+    } catch (SolrException e) {
+      log.error(
+          "Unable to auto-config OpenTelemetry with class {}. Make sure you have enabled the 'opentelemetry' module",
+          DEFAULT_CLASS_NAME,
+          e);
+    }
+    return TraceUtils.getGlobalTracer();
+  }
+
+  /**
+   * best effort way to determine if we should attempt to init OTEL from system properties.
+   *
+   * @return true if OTEL should be init
+   */
+  static boolean shouldAutoConfigOTEL() {
+    boolean isSdkDisabled = Boolean.parseBoolean(getConfig("OTEL_SDK_DISABLED"));
+    if (isSdkDisabled) {
+      return false;
+    }
+    return getConfig("OTEL_SERVICE_NAME") != null;
+  }
+
+  private static String getConfig(String envName) {
+    String envValue = System.getenv().get(envName);
+    String sysName = envName.toLowerCase(Locale.ROOT).replace("_", ".");
+    String sysValue = System.getProperty(sysName);
+    return sysValue != null ? sysValue : envValue;
+  }
 }

solr/core/src/java/org/apache/solr/util/tracing/SimplePropagator.java

@@ -64,7 +64,7 @@ public static synchronized Tracer load() {
       GlobalOpenTelemetry.set(otel);
       loaded = true;
     }
-    return GlobalOpenTelemetry.getTracer("solr");
+    return TraceUtils.getGlobalTracer();
   }
 
   public static TextMapPropagator getInstance() {

solr/core/src/java/org/apache/solr/util/tracing/TraceUtils.java

@@ -22,7 +22,6 @@
 import io.opentelemetry.api.trace.SpanBuilder;
 import io.opentelemetry.api.trace.SpanKind;
 import io.opentelemetry.api.trace.Tracer;
-import io.opentelemetry.api.trace.TracerProvider;
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.propagation.TextMapPropagator;
 import java.util.List;
@@ -36,7 +35,6 @@ public class TraceUtils {
 
   private static final String REQ_ATTR_TRACING_SPAN = Span.class.getName();
   private static final String REQ_ATTR_TRACING_TRACER = Tracer.class.getName();
-  private static final Tracer NOOP_TRACER = TracerProvider.noop().get(null);
 
   public static final String DEFAULT_SPAN_NAME = "http.request";
   public static final String WRITE_QUERY_RESPONSE_SPAN_NAME = "writeQueryResponse";
@@ -66,8 +64,8 @@ public class TraceUtils {
 
   public static final String TAG_DB_TYPE_SOLR = "solr";
 
-  public static Tracer noop() {
-    return NOOP_TRACER;
+  public static Tracer getGlobalTracer() {
+    return GlobalOpenTelemetry.getTracer("solr");
   }
 
   public static TextMapPropagator getTextMapPropagator() {

solr/core/src/test/org/apache/solr/core/TestTracerConfigurator.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.core;
+
+import io.opentelemetry.api.trace.TracerProvider;
+import org.apache.solr.SolrTestCaseJ4;
+import org.apache.solr.util.tracing.TraceUtils;
+import org.junit.Test;
+
+public class TestTracerConfigurator extends SolrTestCaseJ4 {
+
+  @Test
+  public void configuratorClassDoesNotExistTest() {
+    System.setProperty("otel.service.name", "something");
+    System.setProperty("solr.otelDefaultConfigurator", "configuratorClassDoesNotExistTest");
+    try {
+      assertTrue(TracerConfigurator.shouldAutoConfigOTEL());
+      SolrResourceLoader loader = new SolrResourceLoader(TEST_PATH().resolve("collection1"));
+      TracerConfigurator.loadTracer(loader, null);
+      assertEquals(
+          "Expecting noop otel after failure to auto-init",
+          TracerProvider.noop().get(null),
+          TraceUtils.getGlobalTracer());
+    } finally {
+      System.clearProperty("solr.otelDefaultConfigurator");
+      System.clearProperty("otel.service.name");
+    }
+  }
+}

solr/modules/opentelemetry/src/java/org/apache/solr/opentelemetry/OtelTracerConfigurator.java

@@ -16,7 +16,6 @@
  */
 package org.apache.solr.opentelemetry;
 
-import io.opentelemetry.api.GlobalOpenTelemetry;
 import io.opentelemetry.api.trace.Tracer;
 import io.opentelemetry.sdk.autoconfigure.AutoConfiguredOpenTelemetrySdk;
 import java.lang.invoke.MethodHandles;
@@ -28,6 +27,7 @@
 import java.util.stream.Collectors;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.core.TracerConfigurator;
+import org.apache.solr.util.tracing.TraceUtils;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -49,17 +49,17 @@ public OtelTracerConfigurator() {
 
   @Override
   public Tracer getTracer() {
-    // TODO remove reliance on global
-    return GlobalOpenTelemetry.getTracer("solr");
+    return TraceUtils.getGlobalTracer();
   }
 
   @Override
   public void init(NamedList<?> args) {
-    prepareConfiguration();
+    prepareConfiguration(args);
     AutoConfiguredOpenTelemetrySdk.initialize();
   }
 
-  void prepareConfiguration() {
+  void prepareConfiguration(NamedList<?> args) {
+    injectPluginSettingsIfNotConfigured(args);
     setDefaultIfNotConfigured("OTEL_SERVICE_NAME", "solr");
     setDefaultIfNotConfigured("OTEL_TRACES_EXPORTER", "otlp");
     setDefaultIfNotConfigured("OTEL_EXPORTER_OTLP_PROTOCOL", "grpc");
@@ -82,6 +82,20 @@ void prepareConfiguration() {
     System.setProperty("otel.logs.exporter", "none");
   }
 
+  /**
+   * Will inject plugin configuration values into system properties if not already setup (existing
+   * system properties take precedence)
+   */
+  private void injectPluginSettingsIfNotConfigured(NamedList<?> args) {
+    args.forEach(
+        (k, v) -> {
+          var asSysName = envNameToSyspropName(k);
+          if (asSysName.startsWith("otel.")) {
+            setDefaultIfNotConfigured(asSysName, v.toString());
+          }
+        });
+  }
+
   /**
    * Add explicit tags statically to all traces, independent of request. Attributes with same name
    * supplied in ENV or SysProp will take precedence over attributes added in code.

solr/modules/opentelemetry/src/test/org/apache/solr/opentelemetry/CustomTestOtelTracerConfigurator.java

@@ -62,7 +62,7 @@ public static synchronized void prepareForTest() {
 
     // force early init
     CustomTestOtelTracerConfigurator tracer = new CustomTestOtelTracerConfigurator();
-    tracer.prepareConfiguration();
+    tracer.prepareConfiguration(new NamedList<>());
 
     bootOtel();
   }

solr/modules/opentelemetry/src/test/org/apache/solr/opentelemetry/OtelTracerConfiguratorTest.java

@@ -19,6 +19,7 @@
 import java.util.List;
 import java.util.Map;
 import org.apache.solr.SolrTestCaseJ4;
+import org.apache.solr.common.util.NamedList;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -88,9 +89,19 @@ public void testSetDefaultIfNotConfigured() {
   @Test
   public void testResourceAttributes() throws Exception {
     System.setProperty("otel.resource.attributes", "foo=bar,ILLEGAL-LACKS-VALUE,");
-    instance.prepareConfiguration();
+    instance.prepareConfiguration(new NamedList<>());
     assertEquals(
         List.of("host.name=my.solr.host", "foo=bar"),
         List.of(System.getProperty("otel.resource.attributes").split(",")));
   }
+
+  @Test
+  public void testPluginConfig() throws Exception {
+    NamedList<String> conf = new NamedList<>();
+    conf.add("OTEL_K1", "conf-k1"); // will be replaced by sys prop
+    conf.add("otel.k7", "conf-k7"); // will be kept
+    instance.prepareConfiguration(conf);
+    assertEquals("prop-k1", instance.getCurrentOtelConfig().get("OTEL_K1"));
+    assertEquals("conf-k7", instance.getCurrentOtelConfig().get("OTEL_K7"));
+  }
 }