cli: add config kubernetes-versions subcommand (#1224)

Allows users to learn which k8s versions are supported by the
current CLI.
Extend respective docs section.

cli/internal/cmd/config.go

@@ -23,6 +23,7 @@ func NewConfigCmd() *cobra.Command {
 	cmd.AddCommand(newConfigGenerateCmd())
 	cmd.AddCommand(newConfigFetchMeasurementsCmd())
 	cmd.AddCommand(newConfigInstanceTypesCmd())
+	cmd.AddCommand(newConfigKubernetesVersionsCmd())
 
 	return cmd
 }

cli/internal/cmd/configkubernetesversions.go

@@ -0,0 +1,34 @@
+/*
+Copyright (c) Edgeless Systems GmbH
+
+SPDX-License-Identifier: AGPL-3.0-only
+*/
+
+package cmd
+
+import (
+	"strings"
+
+	"github.com/edgelesssys/constellation/v2/internal/versions"
+	"github.com/spf13/cobra"
+)
+
+func newConfigKubernetesVersionsCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "kubernetes-versions",
+		Short: "Print the Kubernetes versions supported by this CLI",
+		Long:  "Print the Kubernetes versions supported by this CLI.",
+		Args:  cobra.ArbitraryArgs,
+		Run:   printSupportedKubernetesVersions,
+	}
+
+	return cmd
+}
+
+func printSupportedKubernetesVersions(cmd *cobra.Command, args []string) {
+	cmd.Printf("Supported Kubernetes Versions:\n\t%s\n", formatKubernetesVersions())
+}
+
+func formatKubernetesVersions() string {
+	return strings.Join(versions.SupportedK8sVersions(), "\n\t")
+}

docs/docs/architecture/versions.md

@@ -10,3 +10,6 @@ New releases are published on [GitHub](https://github.com/edgelesssys/constellat
 ### Kubernetes support policy
 
 Constellation is aligned to the [version support policy of Kubernetes](https://kubernetes.io/releases/version-skew-policy/#supported-versions), and therefore supports the most recent three minor versions.
+When a new minor version is released upstream, the next Constellation release will include four supported Kubernetes versions.
+The fourth version being the newly released Kubernetes version.
+Then, the next Constellation release after that will drop the oldest supported Kubernetes version.

docs/docs/workflows/config.md

@@ -36,7 +36,7 @@ This creates the file `constellation-conf.yaml` in the current directory.
 You can also automatically generate a configuration file by adding the `--generate-config` flag to the `constellation iam create` command when [creating an IAM configuration](#creating-an-iam-configuration).
 :::
 
-## Choosing VM types
+## Choosing a VM type
 
 Constellation supports the following VM types:
 <tabs groupId="csp">
@@ -61,6 +61,11 @@ By default, Constellation uses `m6a.xlarge` VMs (4 vCPUs, 16 GB RAM) to create y
 
 Fill the desired VM type into the **instanceType** field in the `constellation-conf.yml` file.
 
+## Choosing a Kubernetes version
+
+To learn which Kubernetes versions can be installed with your current CLI you can run `constellation config kubernetes-versions`.
+Our support policy for Kubernetes versions is described in [Kubernetes support policy](../architecture/versions.md#kubernetes-support-policy).
+
 ## Creating an IAM configuration
 
 You can create an IAM configuration for your cluster automatically using the `constellation iam create` command.

internal/versions/versions.go

@@ -49,17 +49,13 @@ func NewValidK8sVersion(k8sVersion string) (ValidK8sVersion, error) {
 
 // IsSupportedK8sVersion checks if a given Kubernetes version is supported by Constellation.
 func IsSupportedK8sVersion(version string) bool {
-	switch version {
-	case string(V1_24):
+	for _, valid := range SupportedK8sVersions() {
+		if valid == version {
 			return true
-	case string(V1_25):
-		return true
-	case string(V1_26):
-		return true
-	default:
-		return false
 		}
 	}
+	return false
+}
 
 // IsPreviewK8sVersion checks if a given Kubernetes version is still in preview and not fully supported.
 func IsPreviewK8sVersion(version ValidK8sVersion) bool {