kubeadm: skip upgrade if manifest is not changed

When doing upgrades kubeadm generates new manifest and
waits until kubelet restarts correspondent pod.

However, kubelet won't restart pod if there are no changes
in the manifest. That makes kubeadm stuck waiting for
restarted pod.

Skipping upgrade if new component manifest is the same as
current manifest should solve this.

Fixes: kubernetes/kubeadm#1054

cmd/kubeadm/app/phases/upgrade/BUILD

@@ -37,6 +37,7 @@ go_library(
         "//cmd/kubeadm/app/util/apiclient:go_default_library",
         "//cmd/kubeadm/app/util/dryrun:go_default_library",
         "//cmd/kubeadm/app/util/etcd:go_default_library",
+        "//cmd/kubeadm/app/util/staticpod:go_default_library",
         "//pkg/version:go_default_library",
         "//staging/src/k8s.io/api/apps/v1:go_default_library",
         "//staging/src/k8s.io/api/core/v1:go_default_library",

cmd/kubeadm/app/phases/upgrade/staticpods.go

@@ -32,6 +32,7 @@ import (
 	"k8s.io/kubernetes/cmd/kubeadm/app/util"
 	"k8s.io/kubernetes/cmd/kubeadm/app/util/apiclient"
 	etcdutil "k8s.io/kubernetes/cmd/kubeadm/app/util/etcd"
+	"k8s.io/kubernetes/cmd/kubeadm/app/util/staticpod"
 )
 
 const (
@@ -201,6 +202,16 @@ func upgradeComponent(component string, waiter apiclient.Waiter, pathMgr StaticP
 	// Store the backup path in the recover list. If something goes wrong now, this component will be rolled back.
 	recoverManifests[component] = backupManifestPath
 
+	// Skip upgrade if current and new manifests are equal
+	equal, err := staticpod.ManifestFilesAreEqual(currentManifestPath, newManifestPath)
+	if err != nil {
+		return err
+	}
+	if equal {
+		fmt.Printf("[upgrade/staticpods] current and new manifests of %s are equal, skipping upgrade\n", component)
+		return nil
+	}
+
 	// Move the old manifest into the old-manifests directory
 	if err := pathMgr.MoveFile(currentManifestPath, backupManifestPath); err != nil {
 		return rollbackOldManifests(recoverManifests, err, pathMgr, recoverEtcd)

cmd/kubeadm/app/util/staticpod/utils.go

@@ -17,6 +17,7 @@ limitations under the License.
 package staticpod
 
 import (
+	"bytes"
 	"fmt"
 	"io/ioutil"
 	"net"
@@ -288,3 +289,17 @@ func GetProbeAddress(cfg *kubeadmapi.InitConfiguration, componentName string) st
 	}
 	return "127.0.0.1"
 }
+
+// ManifestFilesAreEqual compares 2 files. It returns true if their contents are equal, false otherwise
+func ManifestFilesAreEqual(path1, path2 string) (bool, error) {
+	content1, err := ioutil.ReadFile(path1)
+	if err != nil {
+		return false, err
+	}
+	content2, err := ioutil.ReadFile(path2)
+	if err != nil {
+		return false, err
+	}
+
+	return bytes.Equal(content1, content2), nil
+}

cmd/kubeadm/app/util/staticpod/utils_test.go

@@ -22,6 +22,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"sort"
+	"strconv"
 	"testing"
 
 	"k8s.io/api/core/v1"
@@ -622,3 +623,73 @@ func TestReadStaticPodFromDisk(t *testing.T) {
 		}
 	}
 }
+
+func TestManifestFilesAreEqual(t *testing.T) {
+	var tests = []struct {
+		description    string
+		podYamls       []string
+		expectedResult bool
+		expectErr      bool
+	}{
+		{
+			description:    "manifests are equal",
+			podYamls:       []string{validPod, validPod},
+			expectedResult: true,
+			expectErr:      false,
+		},
+		{
+			description:    "manifests are not equal",
+			podYamls:       []string{validPod, validPod + "\n"},
+			expectedResult: false,
+			expectErr:      false,
+		},
+		{
+			description:    "first manifest doesn't exist",
+			podYamls:       []string{validPod, ""},
+			expectedResult: false,
+			expectErr:      true,
+		},
+		{
+			description:    "second manifest doesn't exist",
+			podYamls:       []string{"", validPod},
+			expectedResult: false,
+			expectErr:      true,
+		},
+	}
+
+	for _, rt := range tests {
+		tmpdir := testutil.SetupTempDir(t)
+		defer os.RemoveAll(tmpdir)
+
+		// write 2 manifests
+		for i := 0; i < 2; i++ {
+			if rt.podYamls[i] != "" {
+				manifestPath := filepath.Join(tmpdir, strconv.Itoa(i)+".yaml")
+				err := ioutil.WriteFile(manifestPath, []byte(rt.podYamls[i]), 0644)
+				if err != nil {
+					t.Fatalf("Failed to write manifest file\n%s\n\tfatal error: %v", rt.description, err)
+				}
+			}
+		}
+
+		// compare them
+		result, actualErr := ManifestFilesAreEqual(filepath.Join(tmpdir, "0.yaml"), filepath.Join(tmpdir, "1.yaml"))
+		if result != rt.expectedResult {
+			t.Errorf(
+				"ManifestFilesAreEqual failed\n%s\nexpected result: %t\nactual result: %t",
+				rt.description,
+				rt.expectedResult,
+				result,
+			)
+		}
+		if (actualErr != nil) != rt.expectErr {
+			t.Errorf(
+				"ManifestFilesAreEqual failed\n%s\n\texpected error: %t\n\tgot: %t\n\tactual error: %v",
+				rt.description,
+				rt.expectErr,
+				(actualErr != nil),
+				actualErr,
+			)
+		}
+	}
+}