Improving UX for kops validate cluster

Before the `kops validate cluster` attempts to connect to the K8s API
endpoint, the code now checks to see if the API DNS Entry is the kops
placeholder IP Address 203.0.113.123.  It prints a message to the user
and err's.  There is a new init func in validate cluster that disables
CGO based DNS for Darwin OS.  Darwin does two things with kops
validates; it caches the IP address, and it does not return the
placeholder IP address.  We cannot use CGO base DNS with kops validate.

cmd/kops/validate_cluster.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"runtime"
 	"strings"
 
 	"github.com/golang/glog"
@@ -31,10 +32,18 @@ import (
 	"k8s.io/kops/cmd/kops/util"
 	api "k8s.io/kops/pkg/apis/kops"
 	apiutil "k8s.io/kops/pkg/apis/kops/util"
+	"k8s.io/kops/pkg/dns"
 	"k8s.io/kops/pkg/validation"
 	"k8s.io/kops/util/pkg/tables"
 )
 
+func init() {
+	if runtime.GOOS == "darwin" {
+		// In order for  net.LookupHost(apiAddr.Host) to lookup our placeholder address on darwin, we have to
+		os.Setenv("GODEBUG", "netdns=go")
+	}
+}
+
 type ValidateClusterOptions struct {
 	// No options yet
 }
@@ -105,6 +114,25 @@ func RunValidateCluster(f *util.Factory, cmd *cobra.Command, args []string, out
 		return fmt.Errorf("Cannot build kube api client for %q: %v\n", contextName, err)
 	}
 
+	// Do not use if we are running gossip
+	if !dns.IsGossipHostname(cluster.ObjectMeta.Name) {
+		hasPlaceHolderIPAddress, err := validation.HasPlaceHolderIP(contextName)
+		if err != nil {
+			return err
+		}
+
+		if hasPlaceHolderIPAddress {
+			fmt.Println(
+				"Validation Failed\n\n" +
+					"The dns-controller Kubernetes deployment has not updated the Kubernetes cluster's API DNS entry to the correct IP address." +
+					"  The API DNS IP address is the placeholder address that kops creates: 203.0.113.123." +
+					"  Please wait about 5-10 minutes for a master to start, dns-controller to launch, and DNS to propagate." +
+					"  The protokube container and dns-controller deployment logs may contain more diagnostic information." +
+					"  Etcd and the API DNS entries must be updated for a kops Kubernetes cluster to start.")
+			return fmt.Errorf("\nCannot reach cluster's API server: unable to Validate Cluster: %s", cluster.ObjectMeta.Name)
+		}
+	}
+
 	validationCluster, validationFailed := validation.ValidateCluster(cluster.ObjectMeta.Name, list, k8sClient)
 
 	if validationCluster == nil || validationCluster.NodeList == nil || validationCluster.NodeList.Items == nil {

pkg/validation/BUILD.bazel

@@ -17,6 +17,7 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/wait:go_default_library",
         "//vendor/k8s.io/client-go/kubernetes:go_default_library",
+        "//vendor/k8s.io/client-go/tools/clientcmd:go_default_library",
     ],
 )
 

pkg/validation/validate_cluster.go

@@ -18,11 +18,15 @@ package validation
 
 import (
 	"fmt"
+	"net/url"
 	"time"
 
+	"net"
+
 	"k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/client-go/kubernetes"
+	"k8s.io/client-go/tools/clientcmd"
 	"k8s.io/kops/pkg/apis/kops"
 	"k8s.io/kops/pkg/apis/kops/util"
 	"k8s.io/kops/upup/pkg/fi"
@@ -54,6 +58,32 @@ type ValidationNode struct {
 	Status   v1.ConditionStatus `json:"status,omitempty"`
 }
 
+// HasPlaceHolderIP checks if the API DNS has been updated
+func HasPlaceHolderIP(clusterName string) (bool, error) {
+
+	config, err := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
+		clientcmd.NewDefaultClientConfigLoadingRules(),
+		&clientcmd.ConfigOverrides{CurrentContext: clusterName}).ClientConfig()
+
+	apiAddr, err := url.Parse(config.Host)
+	if err != nil {
+		return true, fmt.Errorf("unable to parse Kubernetes cluster API URL: %v", err)
+	}
+
+	hostAddrs, err := net.LookupHost(apiAddr.Host)
+	if err != nil {
+		return true, fmt.Errorf("unable to resolve Kubernetes cluster API URL dns: %v", err)
+	}
+
+	for _, h := range hostAddrs {
+		if h == "203.0.113.123" {
+			return true, nil
+		}
+	}
+
+	return false, nil
+}
+
 // ValidateCluster validate a k8s cluster with a provided instance group list
 func ValidateCluster(clusterName string, instanceGroupList *kops.InstanceGroupList, clusterKubernetesClient kubernetes.Interface) (*ValidationCluster, error) {
 	var instanceGroups []*kops.InstanceGroup