Fix containerFriendly networking in DinD/VM environments

embedded-tests/src/test/java/org/apache/druid/testing/embedded/indexing/KafkaSchemaRegistryResource.java

@@ -50,7 +50,9 @@ public class KafkaSchemaRegistryResource extends TestcontainerResource<RedpandaC
   protected RedpandaContainer createContainer()
   {
     return new RedpandaContainer(SCHEMA_REGISTRY_IMAGE)
-        .dependsOn(kafkaResource.getContainer());
+        .dependsOn(kafkaResource.getContainer())
+        // Enable host.docker.internal on Linux (Docker Desktop provides this automatically)
+        .withExtraHost("host.docker.internal", "host-gateway");
   }
 
   @Override

embedded-tests/src/test/java/org/apache/druid/testing/embedded/k8s/K3sClusterResource.java

@@ -135,7 +135,9 @@ public K3sClusterResource usingDruidManifestTemplate(String resourceName)
   protected K3sContainer createContainer()
   {
     Objects.requireNonNull(druidImageName, "No Druid image specified");
-    final K3sContainer container = new K3sContainer(DockerImageName.parse(K3S_IMAGE_NAME));
+    final K3sContainer container = new K3sContainer(DockerImageName.parse(K3S_IMAGE_NAME))
+        // Enable host.docker.internal on Linux (Docker Desktop provides this automatically)
+        .withExtraHost("host.docker.internal", "host-gateway");
 
     final List<String> portBindings = new ArrayList<>();
     for (K3sDruidService service : services) {

extensions-core/druid-testcontainers/src/main/java/org/apache/druid/testing/DruidContainer.java

@@ -109,6 +109,9 @@ public DruidContainer(DruidCommand command, DockerImageName imageName)
         port -> port + ":" + port
     ).collect(Collectors.toList());
     setPortBindings(portBindings);
+
+    // Enable host.docker.internal on Linux (Docker Desktop provides this automatically)
+    withExtraHost("host.docker.internal", "host-gateway");
   }
 
   /**

extensions-core/kafka-indexing-service/src/test/java/org/apache/druid/indexing/kafka/simulate/KafkaResource.java

@@ -65,22 +65,19 @@ public void beforeStart(EmbeddedDruidCluster cluster)
   @Override
   protected KafkaContainer createContainer()
   {
-    // The result of getBootstrapServers() is the first entry in KafkaContainer.advertisedListeners.
-    // Override getBootstrapServers() to ensure that both DruidContainers and
-    // EmbeddedDruidServers can connect to the Kafka brokers.
-    return new KafkaContainer(KAFKA_IMAGE) {
-      @Override
-      public String getBootstrapServers()
-      {
-        return cluster.getEmbeddedHostname().useInHostAndPort(super.getBootstrapServers());
-      }
-    };
+    return new KafkaContainer(KAFKA_IMAGE)
+        // Enable host.docker.internal on Linux (Docker Desktop provides this automatically)
+        .withExtraHost("host.docker.internal", "host-gateway");
   }
 
+  /**
+   * Returns the Kafka bootstrap server URL, transformed using the cluster's
+   * embedded hostname so it's reachable from both embedded and containerized services.
+   */
   public String getBootstrapServerUrl()
   {
     ensureRunning();
-    return getContainer().getBootstrapServers();
+    return cluster.getEmbeddedHostname().useInHostAndPort(getContainer().getBootstrapServers());
   }
 
   public Map<String, Object> consumerProperties()

services/src/test/java/org/apache/druid/testing/embedded/EmbeddedHostname.java

@@ -21,12 +21,10 @@
 
 import com.google.common.net.HostAndPort;
 import org.apache.druid.java.util.common.IAE;
-import org.apache.druid.java.util.common.ISE;
 import org.apache.http.client.utils.URIBuilder;
+import org.testcontainers.DockerClientFactory;
 
-import java.net.InetAddress;
 import java.net.URISyntaxException;
-import java.net.UnknownHostException;
 
 /**
  * Hostname to be used by embedded services, both Druid and external.
@@ -53,18 +51,20 @@ public static EmbeddedHostname localhost()
   }
 
   /**
-   * Hostname for the host machine running the containers. When a service uses
-   * this hostname instead of {@link #localhost}, it is reachable by Druid
-   * containers and EmbeddedDruidServers alike.
+   * Returns an EmbeddedHostname that is reachable from both embedded services
+   * (running on the host JVM) and containerized services (running in Docker).
+   * <p>
+   * On Linux, this returns the Docker bridge gateway IP (e.g., {@code 172.17.0.1})
+   * which is routable from both the host and containers.
+   * <p>
+   * Note: On Mac/Windows with Docker Desktop, this returns {@code localhost}
+   * which only works for embedded services. Tests mixing embedded and containerized
+   * services should run on Linux.
    */
   public static EmbeddedHostname containerFriendly()
   {
-    try {
-      return new EmbeddedHostname(InetAddress.getLocalHost().getHostAddress());
-    }
-    catch (UnknownHostException e) {
-      throw new ISE(e, "Unable to determine host name");
-    }
+    String dockerHostIp = DockerClientFactory.instance().dockerHostIpAddress();
+    return new EmbeddedHostname(dockerHostIp);
   }
 
   /**