Default LLM Observability ML Application to Service Name

internal-api/src/main/java/datadog/trace/api/Config.java

@@ -2135,7 +2135,9 @@ PROFILING_DATADOG_PROFILER_ENABLED, isDatadogProfilerSafeInCurrentEnvironment())
 
     llmObsAgentlessEnabled =
         configProvider.getBoolean(LLMOBS_AGENTLESS_ENABLED, DEFAULT_LLM_OBS_AGENTLESS_ENABLED);
-    llmObsMlApp = configProvider.getString(LLMOBS_ML_APP);
+    final String tempLlmObsMlApp = configProvider.getString(LLMOBS_ML_APP);
+    llmObsMlApp =
+        tempLlmObsMlApp == null || tempLlmObsMlApp.isEmpty() ? serviceName : tempLlmObsMlApp;
 
     final String llmObsAgentlessUrlStr = getFinalLLMObsUrl();
     URI parsedLLMObsUri = null;
@@ -2642,13 +2644,6 @@ PROFILING_DATADOG_PROFILER_ENABLED, isDatadogProfilerSafeInCurrentEnvironment())
             TRACE_POST_PROCESSING_TIMEOUT, DEFAULT_TRACE_POST_PROCESSING_TIMEOUT);
 
     if (isLlmObsEnabled()) {
-      log.debug("Attempting to enable LLM Observability");
-      if (llmObsMlApp == null || llmObsMlApp.isEmpty()) {
-        throw new IllegalArgumentException(
-            "Attempt to enable LLM Observability without ML app defined."
-                + "Please ensure that the name of the ML app is provided through properties or env variable");
-      }
-
       log.debug(
           "LLM Observability enabled for ML app {}, agentless mode {}",
           llmObsMlApp,

internal-api/src/test/groovy/datadog/trace/api/ConfigTest.groovy

@@ -2332,27 +2332,64 @@ class ConfigTest extends DDSpecification {
     !hostname.trim().isEmpty()
   }
 
-  def "config instantiation should fail if llm obs is enabled via sys prop and ml app is not set"() {
+  def "config instantiation should NOT fail if llm obs is enabled via sys prop and ml app is not set"() {
     setup:
     Properties properties = new Properties()
     properties.setProperty(LLMOBS_ENABLED, "true")
+    properties.setProperty(SERVICE, "test-service")
 
     when:
-    new Config(ConfigProvider.withPropertiesOverride(properties))
+    def config = new Config(ConfigProvider.withPropertiesOverride(properties))
+
+    then:
+    noExceptionThrown()
+    config.isLlmObsEnabled()
+    config.llmObsMlApp == "test-service"
+  }
+
+  def "config instantiation should NOT fail if llm obs is enabled via sys prop and ml app is empty"() {
+    setup:
+    Properties properties = new Properties()
+    properties.setProperty(LLMOBS_ENABLED, "true")
+    properties.setProperty(SERVICE, "test-service")
+    properties.setProperty(LLMOBS_ML_APP, "")
+
+    when:
+    def config = new Config(ConfigProvider.withPropertiesOverride(properties))
 
     then:
-    thrown IllegalArgumentException
+    noExceptionThrown()
+    config.isLlmObsEnabled()
+    config.llmObsMlApp == "test-service"
   }
 
-  def "config instantiation should fail if llm obs is enabled via env var and ml app is not set"() {
+  def "config instantiation should NOT fail if llm obs is enabled via env var and ml app is not set"() {
     setup:
     environmentVariables.set(DD_LLMOBS_ENABLED_ENV, "true")
+    environmentVariables.set(DD_SERVICE_NAME_ENV, "test-service")
 
     when:
-    new Config()
+    def config = new Config()
 
     then:
-    thrown IllegalArgumentException
+    noExceptionThrown()
+    config.isLlmObsEnabled()
+    config.llmObsMlApp == "test-service"
+  }
+
+  def "config instantiation should NOT fail if llm obs is enabled via env var and ml app is empty"() {
+    setup:
+    environmentVariables.set(DD_LLMOBS_ENABLED_ENV, "true")
+    environmentVariables.set(DD_SERVICE_NAME_ENV, "test-service")
+    environmentVariables.set(DD_LLMOBS_ML_APP_ENV, "")
+
+    when:
+    def config = new Config()
+
+    then:
+    noExceptionThrown()
+    config.isLlmObsEnabled()
+    config.llmObsMlApp == "test-service"
   }