Ignore discovery errors for metrics resources

The Metrics API tends to be misconfigured, causing discovery errors which
ultimately makes syncs fail.

This change makes Flux ignore those errors.

cluster/kubernetes/sync.go

@@ -206,6 +206,11 @@ func (c *Cluster) getAllowedResourcesBySelector(selector string) (map[string]*ku
 			return nil, err
 		}
 		for gv, e := range discErr.Groups {
+			if strings.HasSuffix(gv.Group, "metrics.k8s.io") {
+				// The Metrics API tends to be misconfigured, causing errors.
+				// We just ignore them, since it doesn't make sense to sync metrics anyways.
+				continue
+			}
 			// Tolerate empty GroupVersions due to e.g. misconfigured custom metrics
 			if e.Error() != fmt.Sprintf("Got empty response for: %v", gv) {
 				return nil, err

cluster/kubernetes/sync_test.go

@@ -266,7 +266,7 @@ func TestSyncTolerateEmptyGroupVersion(t *testing.T) {
 
 	// Add a GroupVersion without API Resources
 	fakeClient := kube.client.coreClient.(*corefake.Clientset)
-	fakeClient.Resources = append(fakeClient.Resources, &metav1.APIResourceList{GroupVersion: "custom.metrics.k8s.io/v1beta1"})
+	fakeClient.Resources = append(fakeClient.Resources, &metav1.APIResourceList{GroupVersion: "foo.bar/v1"})
 
 	// We should tolerate the error caused in the cache due to the
 	// GroupVersion being empty
@@ -278,6 +278,38 @@ func TestSyncTolerateEmptyGroupVersion(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+type failingDiscoveryClient struct {
+	discovery.DiscoveryInterface
+}
+
+func (d *failingDiscoveryClient) ServerResourcesForGroupVersion(groupVersion string) (*metav1.APIResourceList, error) {
+	return nil, errors.NewServiceUnavailable("")
+}
+
+func TestSyncTolerateMetricsErrors(t *testing.T) {
+	kube, _, cancel := setup(t)
+
+	// Replace the discovery client by one returning errors when asking for resources
+	cancel()
+	crdClient := crdfake.NewSimpleClientset()
+	shutdown := make(chan struct{})
+	defer close(shutdown)
+	newDiscoveryClient := &failingDiscoveryClient{kube.client.coreClient.Discovery()}
+	kube.client.discoveryClient = MakeCachedDiscovery(newDiscoveryClient, crdClient, shutdown)
+
+	// Check that syncing results in an error for groups other than metrics
+	fakeClient := kube.client.coreClient.(*corefake.Clientset)
+	fakeClient.Resources = []*metav1.APIResourceList{{GroupVersion: "foo.bar/v1"}}
+	err := kube.Sync(cluster.SyncSet{})
+	assert.Error(t, err)
+
+	// Check that syncing doesn't result in an error for a metrics group
+	kube.client.discoveryClient.(*cachedDiscovery).CachedDiscoveryInterface.Invalidate()
+	fakeClient.Resources = []*metav1.APIResourceList{{GroupVersion: "custom.metrics.k8s.io/v1"}}
+	err = kube.Sync(cluster.SyncSet{})
+	assert.NoError(t, err)
+}
+
 func TestSync(t *testing.T) {
 	const ns1 = `---
 apiVersion: v1