Document broken behaviour with KUBE_API_VERSIONS

cmd/kube-apiserver/app/server.go

@@ -25,6 +25,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -246,7 +247,15 @@ func Run(s *options.ServerRunOptions) error {
 	}
 	client, err := internalclientset.NewForConfig(selfClientConfig)
 	if err != nil {
-		return fmt.Errorf("failed to create clientset: %v", err)
+		kubeAPIVersions := os.Getenv("KUBE_API_VERSIONS")
+		if len(kubeAPIVersions) == 0 {
+			return fmt.Errorf("failed to create clientset: %v", err)
+		}
+
+		// KUBE_API_VERSIONS is used in test-update-storage-objects.sh, disabling a number of API
+		// groups. This leads to a nil client above and undefined behaviour further down.
+		// TODO: get rid of KUBE_API_VERSIONS or define sane behaviour if set
+		glog.Errorf("Failed to create clientset with KUBE_API_VERSIONS=%q. KUBE_API_VERSIONS is only for testing. Things will break.", kubeAPIVersions)
 	}
 	sharedInformers := informers.NewSharedInformerFactory(nil, client, 10*time.Minute)