Merge pull request #59115 from alexbrand/kubeadm-confirm-reset-2

Automatic merge from submit-queue (batch tested with PRs 59965, 59115, 63076, 63059). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

kubeadm: prompt for confirmation when resetting a master

Signed-off-by: Alexander Brand <alexbrand09@gmail.com>



**What this PR does / why we need it**:
This PR implements a confirmation prompt when running `kubeadm reset` on a master node. This is to prevent users from mistakenly resetting a master node.

**Which issue(s) this PR fixes**:
Fixes https://github.com/kubernetes/kubeadm/issues/673

**Special notes for your reviewer**:
I am somewhat torn on the approach on how to detect that kubeadm is running on a master node. I went with checking for the apiserver manfiest file on the local filesystem, as it seems like a simpler approach when compared to getting a k8s client, getting a list of nodes, finding the current node, and checking if it has the master taint. I am happy to rework if the latter is more desirable.

Sample runs:
```
# ./kubeadm reset
[Warning] Are you sure you want to reset this master node? Type the word "confirm" to continue: no
Aborted reset operation on master node

# ./kubeadm reset
[Warning] Are you sure you want to reset this master node? Type the word "confirm" to continue: confirm
[preflight] Running pre-flight checks.
[reset] Stopping the kubelet service.
[reset] WARNING: The kubelet service could not be stopped by kubeadm: [exit status 1]
[reset] WARNING: Please ensure kubelet is stopped manually.
[reset] Unmounting mounted directories in "/var/lib/kubelet"
........

# ./kubeadm reset
[Warning] Are you sure you want to reset this master node? Type the word "confirm" to continue:
Aborted reset operation on master node
# ./kubeadm reset --confirm
[preflight] Running pre-flight checks.
[reset] Stopping the kubelet service.
[reset] WARNING: The kubelet service could not be stopped by kubeadm: [exit status 1]
[reset] WARNING: Please ensure kubelet is stopped manually.
[reset] Unmounting mounted directories in "/var/lib/kubelet"
........
```

**Release note**:

```release-note
kubeadm: prompt the user for confirmation when resetting a master node
```

cmd/kubeadm/app/cmd/cmd.go

@@ -32,7 +32,7 @@ import (
 )
 
 // NewKubeadmCommand return cobra.Command to run kubeadm command
-func NewKubeadmCommand(_ io.Reader, out, err io.Writer) *cobra.Command {
+func NewKubeadmCommand(in io.Reader, out, err io.Writer) *cobra.Command {
 	cmds := &cobra.Command{
 		Use:   "kubeadm",
 		Short: "kubeadm: easily bootstrap a secure Kubernetes cluster",
@@ -77,7 +77,7 @@ func NewKubeadmCommand(_ io.Reader, out, err io.Writer) *cobra.Command {
 	cmds.AddCommand(NewCmdConfig(out))
 	cmds.AddCommand(NewCmdInit(out))
 	cmds.AddCommand(NewCmdJoin(out))
-	cmds.AddCommand(NewCmdReset(out))
+	cmds.AddCommand(NewCmdReset(in, out))
 	cmds.AddCommand(NewCmdVersion(out))
 	cmds.AddCommand(NewCmdToken(out, err))
 	cmds.AddCommand(upgrade.NewCmdUpgrade(out))

cmd/kubeadm/app/cmd/reset.go

@@ -17,6 +17,8 @@ limitations under the License.
 package cmd
 
 import (
+	"bufio"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -44,11 +46,12 @@ var (
 )
 
 // NewCmdReset returns the "kubeadm reset" command
-func NewCmdReset(out io.Writer) *cobra.Command {
+func NewCmdReset(in io.Reader, out io.Writer) *cobra.Command {
 	var skipPreFlight bool
 	var certsDir string
 	var criSocketPath string
 	var ignorePreflightErrors []string
+	var forceReset bool
 
 	cmd := &cobra.Command{
 		Use:   "reset",
@@ -57,7 +60,7 @@ func NewCmdReset(out io.Writer) *cobra.Command {
 			ignorePreflightErrorsSet, err := validation.ValidateIgnorePreflightErrors(ignorePreflightErrors, skipPreFlight)
 			kubeadmutil.CheckErr(err)
 
-			r, err := NewReset(ignorePreflightErrorsSet, certsDir, criSocketPath)
+			r, err := NewReset(in, ignorePreflightErrorsSet, forceReset, certsDir, criSocketPath)
 			kubeadmutil.CheckErr(err)
 			kubeadmutil.CheckErr(r.Run(out))
 		},
@@ -83,6 +86,11 @@ func NewCmdReset(out io.Writer) *cobra.Command {
 		"The path to the CRI socket to use with crictl when cleaning up containers.",
 	)
 
+	cmd.PersistentFlags().BoolVar(
+		&forceReset, "force", false,
+		"Reset the node without prompting for confirmation.",
+	)
+
 	return cmd
 }
 
@@ -93,9 +101,21 @@ type Reset struct {
 }
 
 // NewReset instantiate Reset struct
-func NewReset(ignorePreflightErrors sets.String, certsDir, criSocketPath string) (*Reset, error) {
+func NewReset(in io.Reader, ignorePreflightErrors sets.String, forceReset bool, certsDir, criSocketPath string) (*Reset, error) {
-	glog.Infoln("[preflight] running pre-flight checks")
+	if !forceReset {
+		fmt.Println("[reset] WARNING: changes made to this host by 'kubeadm init' or 'kubeadm join' will be reverted.")
+		fmt.Print("[reset] are you sure you want to proceed? [y/N]: ")
+		s := bufio.NewScanner(in)
+		s.Scan()
+		if err := s.Err(); err != nil {
+			return nil, err
+		}
+		if strings.ToLower(s.Text()) != "y" {
+			return nil, errors.New("Aborted reset operation")
+		}
+	}
 
+	glog.Infoln("[preflight] running pre-flight checks")
 	if err := preflight.RunRootCheckOnly(ignorePreflightErrors); err != nil {
 		return nil, err
 	}

cmd/kubeadm/app/cmd/reset_test.go

@@ -56,28 +56,31 @@ func assertDirEmpty(t *testing.T, path string) {
 }
 
 func TestNewReset(t *testing.T) {
+	var in io.Reader
 	certsDir := kubeadmapiext.DefaultCertificatesDir
 	criSocketPath := "/var/run/dockershim.sock"
 	skipPreFlight := false
+	forceReset := true
 
 	ignorePreflightErrors := []string{"all"}
 	ignorePreflightErrorsSet, _ := validation.ValidateIgnorePreflightErrors(ignorePreflightErrors, skipPreFlight)
-	NewReset(ignorePreflightErrorsSet, certsDir, criSocketPath)
+	NewReset(in, ignorePreflightErrorsSet, forceReset, certsDir, criSocketPath)
 
 	ignorePreflightErrors = []string{}
 	ignorePreflightErrorsSet, _ = validation.ValidateIgnorePreflightErrors(ignorePreflightErrors, skipPreFlight)
-	NewReset(ignorePreflightErrorsSet, certsDir, criSocketPath)
+	NewReset(in, ignorePreflightErrorsSet, forceReset, certsDir, criSocketPath)
 }
 
 func TestNewCmdReset(t *testing.T) {
 	var out io.Writer
-	cmd := NewCmdReset(out)
+	var in io.Reader
+	cmd := NewCmdReset(in, out)
 
 	tmpDir, err := ioutil.TempDir("", "kubeadm-reset-test")
 	if err != nil {
 		t.Errorf("Unable to create temporary directory: %v", err)
 	}
-	args := []string{"--ignore-preflight-errors=all", "--cert-dir=" + tmpDir}
+	args := []string{"--ignore-preflight-errors=all", "--cert-dir=" + tmpDir, "--force"}
 	cmd.SetArgs(args)
 	if err := cmd.Execute(); err != nil {
 		t.Errorf("Cannot execute reset command: %v", err)