🐛 Add kubernetes server validation on clusterctl

cmd/clusterctl/client/cluster/client.go

@@ -30,6 +30,10 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/client"
 )
 
+const (
+	minimumKubernetesVersion = "v1.16.0"
+)
+
 var (
 	ctx = context.TODO()
 )
@@ -187,6 +191,9 @@ type Proxy interface {
 	// CurrentNamespace returns the namespace from the current context in the kubeconfig file
 	CurrentNamespace() (string, error)
 
+	// ValidateKubernetesVersion returns an error if management cluster version less than minimumKubernetesVersion
+	ValidateKubernetesVersion() error
+
 	// NewClient returns a new controller runtime Client object for working on the management cluster
 	NewClient() (client.Client, error)
 

cmd/clusterctl/client/cluster/inventory.go

@@ -91,6 +91,10 @@ func newInventoryClient(proxy Proxy, pollImmediateWaiter PollImmediateWaiter) *i
 func (p *inventoryClient) EnsureCustomResourceDefinitions() error {
 	log := logf.Log
 
+	if err := p.proxy.ValidateKubernetesVersion(); err != nil {
+		return err
+	}
+
 	// Being this the first connection of many clusterctl operations, we want to fail fast if there is no
 	// connectivity to the cluster, so we try to get a client as a first thing.
 	// NB. NewClient has an internal retry loop that should mitigate temporary connection glitch; here we are

cmd/clusterctl/client/cluster/proxy.go

@@ -23,6 +23,7 @@ import (
 	"github.com/pkg/errors"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	utilversion "k8s.io/apimachinery/pkg/util/version"
 	"k8s.io/client-go/discovery"
 	"k8s.io/client-go/kubernetes"
 	"k8s.io/client-go/rest"
@@ -64,6 +65,30 @@ func (k *proxy) CurrentNamespace() (string, error) {
 	return "default", nil
 }
 
+func (k *proxy) ValidateKubernetesVersion() error {
+	config, err := k.getConfig()
+	if err != nil {
+		return err
+	}
+
+	client := discovery.NewDiscoveryClientForConfigOrDie(config)
+	serverVersion, err := client.ServerVersion()
+	if err != nil {
+		return errors.Wrap(err, "failed to retrieve server version")
+	}
+
+	compver, err := utilversion.MustParseGeneric(serverVersion.String()).Compare(minimumKubernetesVersion)
+	if err != nil {
+		return errors.Wrap(err, "failed to parse and compare server version")
+	}
+
+	if compver == -1 {
+		return errors.Errorf("unsupported management cluster server version: %s - minimum required version is %s", serverVersion.String(), minimumKubernetesVersion)
+	}
+
+	return nil
+}
+
 func (k *proxy) NewClient() (client.Client, error) {
 	config, err := k.getConfig()
 	if err != nil {

cmd/clusterctl/internal/test/fake_proxy.go

@@ -57,6 +57,10 @@ func (f *FakeProxy) CurrentNamespace() (string, error) {
 	return "default", nil
 }
 
+func (f *FakeProxy) ValidateKubernetesVersion() error {
+	return nil
+}
+
 func (f *FakeProxy) NewClient() (client.Client, error) {
 	if f.cs != nil {
 		return f.cs, nil