Select the Feature Flagging configuration source

Author: leoromanovsky

products/feature-flagging/feature-flagging-agent/src/main/java/com/datadog/featureflag/FeatureFlaggingSystem.java

@@ -17,19 +17,37 @@ private FeatureFlaggingSystem() {}
   public static void start(final SharedCommunicationObjects sco) {
     LOGGER.debug("Feature Flagging system starting");
     final Config config = Config.get();
+    CONFIG_SERVICE = createConfigurationSourceService(sco, config);
 
-    if (!config.isRemoteConfigEnabled()) {
-      throw new IllegalStateException("Feature Flagging system started without RC");
+    if (CONFIG_SERVICE != null) {
+      CONFIG_SERVICE.init();
     }
-    CONFIG_SERVICE = new RemoteConfigServiceImpl(sco, config);
-    CONFIG_SERVICE.init();
 
     EXPOSURE_WRITER = new ExposureWriterImpl(sco, config);
     EXPOSURE_WRITER.init();
 
     LOGGER.debug("Feature Flagging system started");
   }
 
+  static ConfigurationSourceService createConfigurationSourceService(
+      final SharedCommunicationObjects sco, final Config config) {
+    final ConfigurationSource configurationSource =
+        ConfigurationSource.from(config.getFeatureFlaggingConfigurationSource());
+
+    if (configurationSource == ConfigurationSource.REMOTE_CONFIG) {
+      if (!config.isRemoteConfigEnabled()) {
+        throw new IllegalStateException("Feature Flagging system started without RC");
+      }
+      return new RemoteConfigServiceImpl(sco, config);
+    }
+    if (configurationSource == ConfigurationSource.AGENTLESS) {
+      return new AgentlessConfigurationSource(config);
+    }
+    LOGGER.debug(
+        "Feature Flagging offline configuration source selected; no config service started");
+    return null;
+  }
+
   public static void stop() {
     if (EXPOSURE_WRITER != null) {
       EXPOSURE_WRITER.close();
@@ -41,4 +59,26 @@ public static void stop() {
     }
     LOGGER.debug("Feature Flagging system stopped");
   }
+
+  private enum ConfigurationSource {
+    AGENTLESS("agentless"),
+    REMOTE_CONFIG("remote_config"),
+    OFFLINE("offline");
+
+    private final String value;
+
+    ConfigurationSource(final String value) {
+      this.value = value;
+    }
+
+    private static ConfigurationSource from(final String value) {
+      for (final ConfigurationSource source : values()) {
+        if (source.value.equals(value)) {
+          return source;
+        }
+      }
+      throw new IllegalArgumentException(
+          "Unsupported Feature Flagging configuration source: " + value);
+    }
+  }
 }

products/feature-flagging/feature-flagging-agent/src/test/java/com/datadog/featureflag/FeatureFlaggingSystemTest.java

@@ -2,6 +2,9 @@
 
 import static datadog.trace.api.config.FeatureFlaggingConfig.FEATURE_FLAGS_CONFIGURATION_SOURCE;
 import static datadog.trace.api.config.RemoteConfigConfig.REMOTE_CONFIGURATION_ENABLED;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.eq;
@@ -64,4 +67,67 @@ void testThatRemoteConfigIsRequired() {
       FeatureFlaggingSystem.stop();
     }
   }
+
+  @Test
+  @WithConfig(key = FEATURE_FLAGS_CONFIGURATION_SOURCE, value = "agentless")
+  @WithConfig(key = REMOTE_CONFIGURATION_ENABLED, value = "false")
+  void agentlessConfigurationSourceUsesHttpServiceWithoutRemoteConfig() {
+    assertInstanceOf(
+        AgentlessConfigurationSource.class,
+        FeatureFlaggingSystem.createConfigurationSourceService(
+            sharedCommunicationObjects(), Config.get()));
+  }
+
+  @Test
+  @WithConfig(key = FEATURE_FLAGS_CONFIGURATION_SOURCE, value = "remote_config")
+  @WithConfig(key = REMOTE_CONFIGURATION_ENABLED, value = "true")
+  void explicitRemoteConfigUsesRemoteConfigService() {
+    SharedCommunicationObjects sharedCommunicationObjects = sharedCommunicationObjects();
+    when(sharedCommunicationObjects.configurationPoller(any(Config.class)))
+        .thenReturn(mock(ConfigurationPoller.class));
+
+    assertInstanceOf(
+        RemoteConfigServiceImpl.class,
+        FeatureFlaggingSystem.createConfigurationSourceService(
+            sharedCommunicationObjects, Config.get()));
+  }
+
+  @Test
+  @WithConfig(key = FEATURE_FLAGS_CONFIGURATION_SOURCE, value = "invalid")
+  void invalidConfigurationSourceFailsBeforeStartingNetworkSource() {
+    assertThrows(
+        IllegalArgumentException.class,
+        () ->
+            FeatureFlaggingSystem.createConfigurationSourceService(
+                sharedCommunicationObjects(), Config.get()));
+  }
+
+  @Test
+  @WithConfig(key = FEATURE_FLAGS_CONFIGURATION_SOURCE, value = "offline")
+  void offlineConfigurationSourceDoesNotStartNetworkSource() {
+    assertNull(
+        FeatureFlaggingSystem.createConfigurationSourceService(
+            sharedCommunicationObjects(), Config.get()));
+  }
+
+  @Test
+  @WithConfig(key = FEATURE_FLAGS_CONFIGURATION_SOURCE, value = "offline")
+  void startWithOfflineConfigurationSourceSkipsConfigService() {
+    try {
+      assertDoesNotThrow(() -> FeatureFlaggingSystem.start(sharedCommunicationObjects()));
+    } finally {
+      FeatureFlaggingSystem.stop();
+    }
+  }
+
+  private static SharedCommunicationObjects sharedCommunicationObjects() {
+    DDAgentFeaturesDiscovery discovery = mock(DDAgentFeaturesDiscovery.class);
+    when(discovery.supportsEvpProxy()).thenReturn(true);
+    when(discovery.getEvpProxyEndpoint()).thenReturn("/evp_proxy/");
+    SharedCommunicationObjects sharedCommunicationObjects = mock(SharedCommunicationObjects.class);
+    when(sharedCommunicationObjects.featuresDiscovery(any(Config.class))).thenReturn(discovery);
+    sharedCommunicationObjects.agentUrl = HttpUrl.get("http://localhost");
+    sharedCommunicationObjects.agentHttpClient = new OkHttpClient.Builder().build();
+    return sharedCommunicationObjects;
+  }
 }

products/feature-flagging/feature-flagging-api/README.md

@@ -85,5 +85,11 @@ OTEL_EXPORTER_OTLP_PROTOCOL=grpc
 ## Requirements
 
 - Java 11+
-- Datadog Agent with Remote Configuration enabled
-- `DD_EXPERIMENTAL_FLAGGING_PROVIDER_ENABLED=true`
+- `DD_FEATURE_FLAGS_CONFIGURATION_SOURCE=agentless` uses the Datadog agentless
+  backend. Set `DD_FEATURE_FLAGS_CONFIGURATION_SOURCE_AGENTLESS_BASE_URL` to a
+  different HTTP backend while keeping agentless delivery semantics. A bare
+  host uses the standard server-distribution path; a URL with a path is used as
+  the exact UFC endpoint. `remote_config` uses the existing Agent Remote
+  Configuration path. `offline` is reserved for startup-provided UFC bytes;
+  until those bytes are implemented, no network source starts and evaluations
+  use defaults.