Print a Warning when the kubernetes service discovery is used without the kubernetes client

core/deployment/src/main/java/io/quarkus/deployment/Capability.java

@@ -80,6 +80,7 @@ public interface Capability {
 
     String QUARTZ = QUARKUS_PREFIX + "quartz";
     String KUBERNETES_SERVICE_BINDING = QUARKUS_PREFIX + "kubernetes.service.binding";
+    String KUBERNETES_CLIENT = QUARKUS_PREFIX + "kubernetes.client";
 
     /**
      * @deprecated

extensions/kubernetes-client/runtime/pom.xml

@@ -63,6 +63,11 @@
             <plugin>
                 <groupId>io.quarkus</groupId>
                 <artifactId>quarkus-bootstrap-maven-plugin</artifactId>
+                <configuration>
+                    <capabilities>
+                        <provides>io.quarkus.kubernetes.client</provides>
+                    </capabilities>
+                </configuration>
             </plugin>
             <plugin>
                 <artifactId>maven-compiler-plugin</artifactId>

extensions/smallrye-stork/deployment/src/main/java/io/quarkus/stork/deployment/SmallRyeStorkProcessor.java

@@ -2,11 +2,18 @@
 
 import static java.util.Arrays.asList;
 
+import org.jboss.logging.Logger;
+
 import io.quarkus.arc.deployment.SyntheticBeansRuntimeInitBuildItem;
+import io.quarkus.bootstrap.classloading.QuarkusClassLoader;
+import io.quarkus.builder.item.EmptyBuildItem;
+import io.quarkus.deployment.Capabilities;
+import io.quarkus.deployment.Capability;
 import io.quarkus.deployment.annotations.BuildProducer;
 import io.quarkus.deployment.annotations.BuildStep;
 import io.quarkus.deployment.annotations.Consume;
 import io.quarkus.deployment.annotations.ExecutionTime;
+import io.quarkus.deployment.annotations.Produce;
 import io.quarkus.deployment.annotations.Record;
 import io.quarkus.deployment.builditem.RuntimeConfigSetupCompleteBuildItem;
 import io.quarkus.deployment.builditem.ShutdownContextBuildItem;
@@ -20,23 +27,55 @@
 
 public class SmallRyeStorkProcessor {
 
+    private static final String KUBERNETES_SERVICE_DISCOVERY_PROVIDER = "io.smallrye.stork.servicediscovery.kubernetes.KubernetesServiceDiscoveryProvider";
+    private static final Logger LOGGER = Logger.getLogger(SmallRyeStorkProcessor.class.getName());
+
     @BuildStep
-    void registerServiceProviders(BuildProducer<ServiceProviderBuildItem> services) {
+    void registerServiceProviders(BuildProducer<ServiceProviderBuildItem> services, Capabilities capabilities) {
         services.produce(new ServiceProviderBuildItem(io.smallrye.stork.spi.config.ConfigProvider.class.getName(),
                 StorkConfigProvider.class.getName()));
-
         for (Class<?> providerClass : asList(LoadBalancerLoader.class, ServiceDiscoveryLoader.class)) {
             services.produce(ServiceProviderBuildItem.allProvidersFromClassPath(providerClass.getName()));
         }
     }
 
+    /**
+     * This build step is the fix for https://github.com/quarkusio/quarkus/issues/24444.
+     * Because Stork itself cannot depend on Quarkus, and we do not want to have extensions for all the service
+     * discovery and load-balancer providers, we work around the issue by detecting when the kubernetes service
+     * discovery is used and if the kubernetes extension is used.
+     */
+    @BuildStep
+    @Produce(AlwaysBuildItem.class)
+    void checkThatTheKubernetesExtensionIsUsedWhenKubernetesServiceDiscoveryInOnTheClasspath(Capabilities capabilities) {
+        if (QuarkusClassLoader.isClassPresentAtRuntime(KUBERNETES_SERVICE_DISCOVERY_PROVIDER)) {
+            if (!capabilities.isPresent(Capability.KUBERNETES_CLIENT)) {
+                LOGGER.warn(
+                        "The application is using the Stork Kubernetes Service Discovery provider but does not depend on the `quarkus-kubernetes-client` extension. "
+                                +
+                                "It is highly recommended to use the `io.quarkus:quarkus-kubernetes-client` extension with the Kubernetes service discovery. \n"
+                                +
+                                "To add this extension:" +
+                                "\n - with the quarkus CLI, run: `quarkus ext add io.quarkus:quarkus-kubernetes-client`" +
+                                "\n - with Apache Maven, run: `./mvnw quarkus:add-extension -Dextensions=\"io.quarkus:quarkus-kubernetes-client\"`"
+                                +
+                                "\n - or just add the `io.quarkus:quarkus-kubernetes-client` dependency to the project");
+            }
+        }
+    }
+
     @BuildStep
     @Record(ExecutionTime.RUNTIME_INIT)
+    @Consume(AlwaysBuildItem.class)
     @Consume(RuntimeConfigSetupCompleteBuildItem.class)
     @Consume(SyntheticBeansRuntimeInitBuildItem.class)
     void initializeStork(SmallRyeStorkRecorder storkRecorder, ShutdownContextBuildItem shutdown, VertxBuildItem vertx,
             StorkConfiguration configuration) {
         storkRecorder.initialize(shutdown, vertx.getVertx(), configuration);
     }
 
+    private static final class AlwaysBuildItem extends EmptyBuildItem {
+        // Just here to be sure we run the `checkThatTheKubernetesExtensionIsUsedWhenKubernetesServiceDiscoveryInOnTheClasspath` build step.
+    }
+
 }