Exclude the metrics APIs from resources discovery

go.sum

@@ -10,6 +10,7 @@ github.com/Azure/go-autorest v11.7.1+incompatible h1:M2YZIajBBVekV86x0rr1443Lc1F
 github.com/Azure/go-autorest v11.7.1+incompatible/go.mod h1:r+4oMnoxhatjLLJ6zxSWATqVooLgysK6ZNox3g/xq24=
 github.com/BurntSushi/toml v0.3.1 h1:WXkYYl6Yr3qBf1K79EBnL4mak0OimBfB0XUf9Vl28OQ=
 github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802 h1:1BDTz0u9nC3//pOCMdNH+CiXJVYJh5UQNCOBG7jbELc=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
 github.com/Jeffail/gabs v1.4.0 h1://5fYRRTq1edjfIrQGvdkcd22pkYUrHZ5YC/H2GJVAo=
 github.com/Jeffail/gabs v1.4.0/go.mod h1:6xMvQMK4k33lb7GUUpaAPh6nKMmemQeg5d4gn7/bOXc=

pkg/cluster/kubernetes/sync.go

@@ -22,7 +22,6 @@ import (
 	meta_v1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/apimachinery/pkg/runtime/schema"
-	"k8s.io/client-go/discovery"
 	"k8s.io/client-go/rest"
 
 	"github.com/fluxcd/flux/pkg/cluster"
@@ -208,21 +207,23 @@ func (c *Cluster) getAllowedResourcesBySelector(selector string) (map[string]*ku
 		listOptions.LabelSelector = selector
 	}
 
-	_, resources, err := c.client.discoveryClient.ServerGroupsAndResources()
-	if err != nil {
-		discErr, ok := err.(*discovery.ErrGroupDiscoveryFailed)
-		if !ok {
-			return nil, err
-		}
-		for gv, e := range discErr.Groups {
-			if gv.Group == "metrics" || 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
+	sgs, err := c.client.discoveryClient.ServerGroups()
+	if sgs == nil {
+		return nil, err
+	}
+
+	resources := []*meta_v1.APIResourceList{}
+	for i := range sgs.Groups {
+		gv := sgs.Groups[i].PreferredVersion.GroupVersion
+		// exclude the *.metrics.k8s.io resources to avoid querying the cluster metrics
+		if !strings.Contains(sgs.Groups[i].Name, "metrics.k8s.io") {
+			if r, err := c.client.discoveryClient.ServerResourcesForGroupVersion(gv); err == nil {
+				resources = append(resources, r)
+			} else {
+				// ignore errors for resources with empty group version instead of failing to sync
+				if err.Error() != fmt.Sprintf("Got empty response for: %v", gv) {
+					return nil, err
+				}
 			}
 		}
 	}
@@ -239,6 +240,9 @@ func (c *Cluster) getAllowedResourcesBySelector(selector string) (map[string]*ku
 	}
 
 	for _, resource := range resources {
+		if resource == nil {
+			continue
+		}
 		for _, apiResource := range resource.APIResources {
 			verbs := apiResource.Verbs
 			if !contains(verbs, "list") {