patch kubeadm for dualstack 1.20

pkg/cluster/internal/create/create.go

@@ -22,9 +22,11 @@ import (
 	"time"
 
 	"github.com/alessio/shellescape"
+	"k8s.io/apimachinery/pkg/util/version"
 
 	"sigs.k8s.io/kind/pkg/cluster/internal/delete"
 	"sigs.k8s.io/kind/pkg/cluster/internal/providers"
+	"sigs.k8s.io/kind/pkg/cluster/nodeutils"
 	"sigs.k8s.io/kind/pkg/errors"
 	"sigs.k8s.io/kind/pkg/internal/apis/config"
 	"sigs.k8s.io/kind/pkg/internal/apis/config/encoding"
@@ -106,6 +108,11 @@ func Cluster(logger log.Logger, p providers.Provider, opts *ClusterOptions) erro
 		return err
 	}
 
+	// TODO: remove once 1.20 is EOL or we no longer want to support dual-stack in 1.20 images
+	if err := fixupDualStack(p, opts.Config); err != nil {
+		return err
+	}
+
 	// TODO(bentheelder): make this controllable from the command line?
 	actionsToRun := []actions.Action{
 		loadbalancer.NewAction(), // setup external loadbalancer
@@ -255,3 +262,64 @@ func validateProvider(p providers.Provider) error {
 	}
 	return nil
 }
+
+// fixupDualStack enables the Kubeadm feature gate if kubernetes version is 1.20
+// previous versions doesn't support dual-stack so it returns an error
+// 1.21+ enable the feature gate by default
+func fixupDualStack(p providers.Provider, cfg *config.Cluster) error {
+	// return early if is not dualstack
+	if cfg.Networking.IPFamily != config.DualStackFamily {
+		return nil
+	}
+
+	// we need to obtain the kubernetes version from the nodes
+	name := cfg.Name
+	n, err := p.ListNodes(name)
+	if err != nil {
+		return err
+	}
+	if len(n) == 0 {
+		return errors.New("no nodes found")
+	}
+	// use the first control plane node available
+	// we validate against the apiserver version.
+	node, err := nodeutils.BootstrapControlPlaneNode(n)
+	if err != nil {
+		return err
+	}
+	kubeVersion, err := nodeutils.KubeVersion(node)
+	if err != nil {
+		return errors.Wrapf(err, "failed to get kubernetes version from node %s", node.String())
+	}
+	ver, err := version.ParseSemantic(kubeVersion)
+	if err != nil {
+		return errors.Wrapf(err, "failed to parse node version %s", kubeVersion)
+	}
+
+	// dual-stack is only supported in 1.20+
+	if ver.LessThan(version.MustParseSemantic("v1.20.0")) {
+		return errors.New("failed to create cluster, dual-stack is only supported on Kubernetes versions 1.20+")
+	}
+
+	// dual-stack feature gate is enabled by default since 1.21
+	if ver.AtLeast(version.MustParseSemantic("v1.21.0")) {
+		return nil
+	}
+
+	// for 1.20 we have to explicitly enable the feature gate
+	// we can patch kubeadm here so we avoid to plumb this hack further
+	dualPatch := `
+apiVersion: kubeadm.k8s.io/v1beta2
+kind: ClusterConfiguration
+metadata:
+  name: config
+featureGates:
+  IPv6DualStack: true
+`
+	if len(cfg.KubeadmConfigPatches) > 0 {
+		cfg.KubeadmConfigPatches = append(cfg.KubeadmConfigPatches, dualPatch)
+	} else {
+		cfg.KubeadmConfigPatches = []string{dualPatch}
+	}
+	return nil
+}