Check if vcluster version supports k8s version

Prior, an extra value, distro.k8s.version, could be set for a vcluster
with a version that does not support the distro.k8s.version field.
This would lead to a panic in vcluster. Now, the value is only set if
the vcluster chart version is known to support it. Otherwise, it is
left empty, leading to the omission of the field and no panic.

fix

config/default_extra_values.go

@@ -5,6 +5,8 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+
+	"github.com/blang/semver"
 )
 
 const (
@@ -71,6 +73,16 @@ var K8SEtcdVersionMap = map[string]string{
 	"1.27": "registry.k8s.io/etcd:3.5.7-0",
 }
 
+var vclusterVersionsWithK8sVersionSupport []semver.Version
+
+func init() {
+	vclusterVersionsWithK8sVersionSupport = []semver.Version{
+		semver.MustParse("0.20.0-beta.16"),
+		semver.MustParse("0.20.0-alpha.99"),
+		semver.MustParse("0.21.0-alpha.4"),
+	}
+}
+
 // ExtraValuesOptions holds the chart options
 type ExtraValuesOptions struct {
 	Distro string
@@ -91,21 +103,21 @@ type KubernetesVersion struct {
 	Minor string
 }
 
-func GetExtraValues(options *ExtraValuesOptions) (string, error) {
+func GetExtraValues(options *ExtraValuesOptions, chartVersion string) (string, error) {
 	fromConfig, err := NewDefaultConfig()
 	if err != nil {
 		return "", err
 	}
 
-	toConfig, err := getExtraValues(options)
+	toConfig, err := getExtraValues(options, chartVersion)
 	if err != nil {
 		return "", fmt.Errorf("get extra values: %w", err)
 	}
 
 	return Diff(fromConfig, toConfig)
 }
 
-func getExtraValues(options *ExtraValuesOptions) (*Config, error) {
+func getExtraValues(options *ExtraValuesOptions, chartVersion string) (*Config, error) {
 	vConfig, err := NewDefaultConfig()
 	if err != nil {
 		return nil, err
@@ -124,7 +136,7 @@ func getExtraValues(options *ExtraValuesOptions) (*Config, error) {
 	}
 
 	// apply k8s values
-	err = applyK8SExtraValues(vConfig, options)
+	err = applyK8SExtraValues(vConfig, options, chartVersion)
 	if err != nil {
 		return nil, err
 	}
@@ -166,7 +178,7 @@ func applyK0SExtraValues(vConfig *Config, options *ExtraValuesOptions) error {
 	return nil
 }
 
-func applyK8SExtraValues(vConfig *Config, options *ExtraValuesOptions) error {
+func applyK8SExtraValues(vConfig *Config, options *ExtraValuesOptions, chartVersion string) error {
 	// get api server image
 	apiImage, err := getImageByVersion(options.KubernetesVersion, K8SAPIVersionMap)
 	if err != nil {
@@ -180,16 +192,63 @@ func applyK8SExtraValues(vConfig *Config, options *ExtraValuesOptions) error {
 	}
 
 	// build values
-	if apiImage != "" {
-		vConfig.ControlPlane.Distro.K8S.Version = parseImage(apiImage).Tag
+	k8sVersion, err := getK8sVersion(chartVersion, apiImage)
+	if err != nil {
+		return err
 	}
+	vConfig.ControlPlane.Distro.K8S.Version = k8sVersion
+
 	if etcdImage != "" {
 		vConfig.ControlPlane.BackingStore.Etcd.Deploy.StatefulSet.Image = parseImage(etcdImage)
 	}
 
 	return nil
 }
 
+func getK8sVersion(chartVersion, apiImage string) (string, error) {
+	if apiImage == "" {
+		return "", nil
+	}
+	isSupported, err := isK8sVersionSupported(chartVersion)
+	if err != nil {
+		return "", err
+	}
+
+	if isSupported {
+		return parseImage(apiImage).Tag, nil
+	}
+	// if we set a non-empty value for a vcluster chart version that does not support
+	// the k8s version field, vcluster will panic
+	return "", nil
+}
+
+func isK8sVersionSupported(chartVersion string) (bool, error) {
+	if chartVersion == "" {
+		// probably dev chart
+		return true, nil
+	}
+	v, err := semver.Parse(strings.TrimPrefix(chartVersion, "v"))
+	if err != nil {
+		return false, err
+	}
+	for _, supportedStartVer := range vclusterVersionsWithK8sVersionSupport {
+		if v.Minor != supportedStartVer.Minor {
+			continue
+		}
+		if len(supportedStartVer.Pre) > 0 && len(v.Pre) > 0 && supportedStartVer.Pre[0] != v.Pre[0] {
+			// this is a special case- its possible in our releases for an alpha to be ahead of a beta;
+			// we cannot compare prebuilds unless they share the same first element.
+			return true, nil
+		}
+		if v.GTE(supportedStartVer) {
+			return true, nil
+		}
+		return false, nil
+	}
+	// in the case no relevant start version was found for minor we can assume k8s version is supported
+	return true, nil
+}
+
 func parseImage(image string) Image {
 	registry, repository, tag := SplitImage(image)
 	return Image{

pkg/cli/create_helm.go

@@ -265,7 +265,7 @@ func CreateHelm(ctx context.Context, options *CreateOptions, globalFlags *flags.
 	if err != nil {
 		return err
 	}
-	chartValues, err := config.GetExtraValues(chartOptions)
+	chartValues, err := config.GetExtraValues(chartOptions, options.ChartVersion)
 	if err != nil {
 		return err
 	}

pkg/cli/create_platform.go

@@ -612,7 +612,7 @@ func mergeValues(platformClient platform.Client, options *CreateOptions, log log
 	if err != nil {
 		return "", err
 	}
-	chartValues, err := vclusterconfig.GetExtraValues(chartOptions)
+	chartValues, err := vclusterconfig.GetExtraValues(chartOptions, options.ChartVersion)
 	if err != nil {
 		return "", err
 	}