feat: Controllers can now watch only the namespace they're deployed in

This is achieved by using `JOSDK_WATCH_CURRENT` as the only value of the
namespaces configuration for the controller.

Fixes #372

Author: metacosm

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/Operator.java

@@ -58,7 +58,7 @@ public void start() {
    * Registers the specified controller with this operator.
    *
    * @param controller the controller to register
-   * @param <R> the {@code CustomResource} type associated with the controller
+   * @param <R>        the {@code CustomResource} type associated with the controller
    * @throws OperatorException if a problem occurred during the registration process
    */
   public <R extends CustomResource> void register(ResourceController<R> controller)
@@ -68,14 +68,13 @@ public <R extends CustomResource> void register(ResourceController<R> controller
 
   /**
    * Registers the specified controller with this operator, overriding its default configuration by
-   * the specified one (usually created via {@link
-   * io.javaoperatorsdk.operator.api.config.ControllerConfigurationOverrider#override(ControllerConfiguration)},
+   * the specified one (usually created via {@link io.javaoperatorsdk.operator.api.config.ControllerConfigurationOverrider#override(ControllerConfiguration)},
    * passing it the controller's original configuration.
    *
-   * @param controller the controller to register
+   * @param controller    the controller to register
    * @param configuration the configuration with which we want to register the controller, if {@code
-   *     null}, the controller's original configuration is used
-   * @param <R> the {@code CustomResource} type associated with the controller
+   *                      null}, the controller's original configuration is used
+   * @param <R>           the {@code CustomResource} type associated with the controller
    * @throws OperatorException if a problem occurred during the registration process
    */
   public <R extends CustomResource> void register(
@@ -95,7 +94,15 @@ public <R extends CustomResource> void register(
       }
 
       final var retry = GenericRetry.fromConfiguration(configuration.getRetryConfiguration());
-      final var targetNamespaces = configuration.getNamespaces().toArray(new String[] {});
+
+      // check if we only want to watch the current namespace
+      var targetNamespaces = configuration.getNamespaces().toArray(new String[]{});
+      if (configuration.watchCurrentNamespace()) {
+        targetNamespaces = new String[]{
+            configurationService.getClientConfiguration().getNamespace()
+        };
+      }
+
       Class<R> resClass = configuration.getCustomResourceClass();
       String finalizer = configuration.getFinalizer();
 
@@ -164,7 +171,7 @@ private CustomResourceEventSource createCustomResourceEventSource(
     CustomResourceEventSource customResourceEventSource =
         watchAllNamespaces
             ? CustomResourceEventSource.customResourceEventSourceForAllNamespaces(
-                customResourceCache, client, generationAware, finalizer)
+            customResourceCache, client, generationAware, finalizer)
             : CustomResourceEventSource.customResourceEventSourceForTargetNamespaces(
                 customResourceCache, client, targetNamespaces, generationAware, finalizer);
 

operator-framework-core/src/main/java/io/javaoperatorsdk/operator/api/config/ControllerConfiguration.java

@@ -5,6 +5,7 @@
 import java.util.Set;
 
 public interface ControllerConfiguration<R extends CustomResource> {
+  String WATCH_CURRENT_NAMESPACE = "JOSDK_WATCH_CURRENT";
   String getName();
 
   String getCRDName();
@@ -25,6 +26,11 @@ default boolean watchAllNamespaces() {
     return getNamespaces().isEmpty();
   }
 
+  default boolean watchCurrentNamespace() {
+    final var namespaces = getNamespaces();
+    return namespaces.size() == 1 && namespaces.contains(WATCH_CURRENT_NAMESPACE);
+  }
+
   default RetryConfiguration getRetryConfiguration() {
     return RetryConfiguration.DEFAULT;
   }