Registry reachable in cluster

internal/cluster/init.go

@@ -135,6 +135,14 @@ func (c *Cluster) Init(ctx context.Context, opts InitOptions) error {
 		return fmt.Errorf("failed to install CoreDNS: %w", err)
 	}
 
+	// Enable fallthrough in CoreDNS so that non-Kubernetes cluster.local names
+	// (e.g. registry.cluster.local) are forwarded to the bink DNS container.
+	c.logger.Info("")
+	c.logger.Info("=== Patching CoreDNS for cluster.local fallthrough ===")
+	if err := kubeClient.EnableCoreDNSFallthrough(ctx); err != nil {
+		return fmt.Errorf("failed to enable CoreDNS fallthrough: %w", err)
+	}
+
 	// Patch CoreDNS to run as root - CRI-O doesn't set ambient capabilities
 	// for non-root users, so NET_BIND_SERVICE doesn't take effect for UID 65532
 	c.logger.Info("")

internal/kube/resources.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"strings"
 	"time"
 
 	policyv1 "k8s.io/api/policy/v1"
@@ -127,6 +128,34 @@ func (c *Client) DeleteNode(ctx context.Context, nodeName string) error {
 	return nil
 }
 
+// EnableCoreDNSFallthrough patches the CoreDNS ConfigMap so that unresolved
+// cluster.local queries fall through to the forward plugin (which reaches the
+// bink dnsmasq container via the node's /etc/resolv.conf).
+func (c *Client) EnableCoreDNSFallthrough(ctx context.Context) error {
+	cm, err := c.clientset.CoreV1().ConfigMaps("kube-system").Get(ctx, "coredns", metav1.GetOptions{})
+	if err != nil {
+		return fmt.Errorf("getting coredns ConfigMap: %w", err)
+	}
+
+	corefile, ok := cm.Data["Corefile"]
+	if !ok {
+		return fmt.Errorf("Corefile key not found in coredns ConfigMap")
+	}
+
+	updated := strings.Replace(corefile, "fallthrough in-addr.arpa ip6.arpa", "fallthrough", 1)
+	if updated == corefile {
+		return nil
+	}
+
+	cm.Data["Corefile"] = updated
+	_, err = c.clientset.CoreV1().ConfigMaps("kube-system").Update(ctx, cm, metav1.UpdateOptions{})
+	if err != nil {
+		return fmt.Errorf("updating coredns ConfigMap: %w", err)
+	}
+
+	return nil
+}
+
 // LabelNode adds the given labels to a node, overwriting any that already exist.
 func (c *Client) LabelNode(ctx context.Context, nodeName string, labels map[string]string) error {
 	patch := map[string]interface{}{

test/integration/cluster_test.go

@@ -143,6 +143,12 @@ var _ = Describe("Cluster Lifecycle", func() {
 			Expect(err).ToNot(HaveOccurred())
 			Expect(pod.Status.Phase).To(Equal(corev1.PodRunning))
 
+			By("Verifying pod can resolve registry.cluster.local via CoreDNS")
+			nslookupOutput, err := helpers.PodExec(kubeconfigPath, "default", "busybox-test",
+				[]string{"nslookup", "registry.cluster.local"})
+			Expect(err).ToNot(HaveOccurred(), "nslookup registry.cluster.local should succeed from pod")
+			Expect(nslookupOutput).To(ContainSubstring(config.RegistryStaticIP))
+
 			By("Cleaning up the busybox pod")
 			helpers.DeletePod(kubeClient, "default", "busybox-test")