kubernetes
diff --git a/‎cmd/kops/create_cluster.go‎
Lines changed: 14 additions & 0 deletions b/‎cmd/kops/create_cluster.go‎
Lines changed: 14 additions & 0 deletions
diff --git a/‎cmd/kops/create_cluster_test.go‎
Lines changed: 22 additions & 0 deletions b/‎cmd/kops/create_cluster_test.go‎
Lines changed: 22 additions & 0 deletions
@@ -212,6 +212,10 @@ func NewCmdCreateCluster(f *util.Factory, out io.Writer) *cobra.Command {
 				options.EncryptEtcdStorage = &encryptEtcdStorage
 			}
 
+			if err := checkProjectFlag(cmd.Flag("project").Changed, options.Project); err != nil {
+				return err
+			}
+
 			if sshPublicKey != "" {
 				options.SSHPublicKeys, err = loadSSHPublicKeys(sshPublicKey)
 				if err != nil {
@@ -931,6 +935,16 @@ func RunCreateCluster(ctx context.Context, f *util.Factory, out io.Writer, c *Cr
 	return nil
 }
 
+// checkProjectFlag rejects an explicitly empty --project flag. An empty value usually comes from
+// an unset environment variable (e.g. --project=$PROJECT); silently accepting it would fall back
+// to the gcloud default project, which may not be the intended one.
+func checkProjectFlag(flagSet bool, project string) error {
+	if flagSet && project == "" {
+		return fmt.Errorf("--project cannot be empty; specify a project or omit the flag to use the gcloud default project")
+	}
+	return nil
+}
+
 // parseCloudLabels takes a CSV list of key=value records and parses them into a map. Nested '='s are supported via
 // quoted strings (eg `foo="bar=baz"` parses to map[string]string{"foo":"bar=baz"}. Nested commas are not supported.
 func parseCloudLabels(s string) (map[string]string, error) {
 
@@ -20,6 +20,28 @@ import (
 	"testing"
 )
 
+func TestCheckProjectFlag(t *testing.T) {
+	grid := []struct {
+		flagSet   bool
+		project   string
+		shouldErr bool
+	}{
+		{flagSet: false, project: "", shouldErr: false},
+		{flagSet: true, project: "my-project", shouldErr: false},
+		{flagSet: true, project: "", shouldErr: true},
+	}
+
+	for _, g := range grid {
+		err := checkProjectFlag(g.flagSet, g.project)
+		if g.shouldErr && err == nil {
+			t.Errorf("checkProjectFlag(%v, %q): expected error, got nil", g.flagSet, g.project)
+		}
+		if !g.shouldErr && err != nil {
+			t.Errorf("checkProjectFlag(%v, %q): unexpected error: %v", g.flagSet, g.project, err)
+		}
+	}
+}
+
 func TestParseCloudLabels(t *testing.T) {
 	expect := map[string]string{"foo": "bar", "fib": "baz"}
 	checkParse(t, "", map[string]string{}, false)