Allow specifying the latest version for a release channel

go.mod

@@ -10,6 +10,7 @@ require (
 	github.com/spf13/cobra v1.0.0
 	github.com/spf13/pflag v1.0.5
 	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
+	gopkg.in/yaml.v2 v2.2.8
 	k8s.io/klog v1.0.0
 	sigs.k8s.io/boskos v0.0.0-20200710214748-f5935686c7fc
 )

kubetest2-gke/deployer/commandutils.go

@@ -22,6 +22,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"gopkg.in/yaml.v2"
 	"k8s.io/klog"
 
 	"sigs.k8s.io/kubetest2/pkg/exec"
@@ -116,3 +117,36 @@ func getClusterCredentials(project, loc, cluster string) error {
 
 	return nil
 }
+
+// Resolve the current latest version in the given release channel.
+func resolveLatestVersionInChannel(loc, channelName string) (string, error) {
+	// Get the server config for the current location.
+	out, err := exec.Output(exec.RawCommand(
+		fmt.Sprintf("gcloud container get-server-config --format=\"yaml(channels:format='yaml(channel,validVersions)')\" %s", loc)))
+	if err != nil {
+		return "", fmt.Errorf("failed to get the server config: %w", err)
+	}
+
+	type Channel struct {
+		Name          string   `yaml:"channel"`
+		ValidVersions []string `yaml:"validVersions"`
+	}
+	type Channels struct {
+		Channels []Channel `yaml:"channels"`
+	}
+	var cs Channels
+	if err = yaml.Unmarshal(out, &cs); err != nil {
+		return "", fmt.Errorf("failed to unmarshal the server config: %w", err)
+	}
+
+	for _, channel := range cs.Channels {
+		if strings.EqualFold(channel.Name, channelName) {
+			if len(channel.ValidVersions) == 0 {
+				return "", fmt.Errorf("no valid versions for channel %q", channelName)
+			}
+			return channel.ValidVersions[0], nil
+		}
+	}
+
+	return "", fmt.Errorf("channel %q does not exist in the server config", channelName)
+}

kubetest2-gke/deployer/deployer.go

@@ -88,7 +88,7 @@ type deployer struct {
 
 	RepoRoot       string `desc:"Path to root of the kubernetes repo. Used with --build and for dumping cluster logs."`
 	ReleaseChannel string `desc:"Use a GKE release channel, could be one of empty, rapid, regular and stable - https://cloud.google.com/kubernetes-engine/docs/concepts/release-channels"`
-	Version        string `desc:"Use a specific GKE version e.g. 1.16.13.gke-400 or 'latest'. If --build is specified it will default to building kubernetes from source."`
+	Version        string `desc:"Use a specific GKE version e.g. 1.16.13.gke-400, 'latest' or ''. If --build is specified it will default to building kubernetes from source."`
 
 	// doInit helps to make sure the initialization is performed only once
 	doInit sync.Once
@@ -166,7 +166,8 @@ func New(opts types.Options) (types.Deployer, *pflag.FlagSet) {
 			NumClusters: 1,
 		},
 		localLogsDir: filepath.Join(opts.ArtifactsDir(), "logs"),
-		Version:      "latest",
+		// Leave Version as empty to use the default cluster version.
+		Version: "",
 	}
 
 	// register flags

kubetest2-gke/deployer/up.go

@@ -88,8 +88,15 @@ func (d *deployer) Up() error {
 				}
 				if d.ReleaseChannel != "" {
 					args = append(args, "--release-channel="+d.ReleaseChannel)
-					// --cluster-version must be a specific valid version if --release-channel is not empty.
-					if d.Version != "latest" {
+					if d.Version == "latest" {
+						// If latest is specified, get the latest version from server config for this channel.
+						actualVersion, err := resolveLatestVersionInChannel(loc, d.ReleaseChannel)
+						if err != nil {
+							return err
+						}
+						klog.V(0).Infof("Using the latest version %q in %q channel", actualVersion, d.ReleaseChannel)
+						args = append(args, "--cluster-version="+actualVersion)
+					} else {
 						args = append(args, "--cluster-version="+d.Version)
 					}
 				} else {
@@ -264,7 +271,7 @@ func generateClusterNames(numClusters int, uid string) []string {
 
 func validateVersion(version string) error {
 	switch version {
-	case "latest":
+	case "latest", "":
 		return nil
 	default:
 		re, err := regexp.Compile(`(\d)\.(\d)+\.(\d)*(.*)`)