Kubeadm: Add some validation for external etcd config

cmd/kubeadm/app/preflight/checks.go

@@ -677,6 +677,15 @@ func RunInitMasterChecks(cfg *kubeadmapi.MasterConfiguration) error {
 		)
 	} else {
 		// Only check etcd version when external endpoints are specified
+		if cfg.Etcd.CAFile != "" {
+			checks = append(checks, FileExistingCheck{Path: cfg.Etcd.CAFile})
+		}
+		if cfg.Etcd.CertFile != "" {
+			checks = append(checks, FileExistingCheck{Path: cfg.Etcd.CertFile})
+		}
+		if cfg.Etcd.KeyFile != "" {
+			checks = append(checks, FileExistingCheck{Path: cfg.Etcd.KeyFile})
+		}
 		checks = append(checks,
 			ExternalEtcdVersionCheck{Etcd: cfg.Etcd},
 		)

cmd/kubeadm/app/preflight/checks_test.go

@@ -174,24 +174,47 @@ func (pfct preflightCheckTest) Check() (warning, errors []error) {
 
 func TestRunInitMasterChecks(t *testing.T) {
 	var tests = []struct {
+		name     string
 		cfg      *kubeadmapi.MasterConfiguration
 		expected bool
 	}{
-		{
+		{name: "Test valid advertised address",
 			cfg: &kubeadmapi.MasterConfiguration{
 				API: kubeadmapi.API{AdvertiseAddress: "foo"},
 			},
 			expected: false,
 		},
+		{
+			name: "Test CA file exists if specfied",
+			cfg: &kubeadmapi.MasterConfiguration{
+				Etcd: kubeadmapi.Etcd{CAFile: "/foo"},
+			},
+			expected: false,
+		},
+		{
+			name: "Test Cert file exists if specfied",
+			cfg: &kubeadmapi.MasterConfiguration{
+				Etcd: kubeadmapi.Etcd{CertFile: "/foo"},
+			},
+			expected: false,
+		},
+		{
+			name: "Test Key file exists if specfied",
+			cfg: &kubeadmapi.MasterConfiguration{
+				Etcd: kubeadmapi.Etcd{CertFile: "/foo"},
+			},
+			expected: false,
+		},
 	}
 
 	for _, rt := range tests {
 		actual := RunInitMasterChecks(rt.cfg)
 		if (actual == nil) != rt.expected {
 			t.Errorf(
-				"failed RunInitMasterChecks:\n\texpected: %t\n\t  actual: %t",
+				"failed RunInitMasterChecks:\n\texpected: %t\n\t  actual: %t\n\t error: %v",
 				rt.expected,
-				(actual != nil),
+				(actual == nil),
+				actual,
 			)
 		}
 	}