Add option to add the ssh-host key to known_hosts

This matches the ssh-add command for identity keys,
it will add the host key to the ssh known_hosts file.

If a ssh key for the host already exists in the file,
it will not be added again so can be run multiple times.

cmd/minikube/cmd/ssh-host.go

@@ -19,8 +19,10 @@ package cmd
 import (
 	"fmt"
 	"os"
+	"path/filepath"
 
 	"github.com/spf13/cobra"
+	"k8s.io/client-go/util/homedir"
 
 	"k8s.io/minikube/pkg/minikube/config"
 	"k8s.io/minikube/pkg/minikube/driver"
@@ -30,6 +32,11 @@ import (
 	"k8s.io/minikube/pkg/minikube/node"
 	"k8s.io/minikube/pkg/minikube/out"
 	"k8s.io/minikube/pkg/minikube/reason"
+	"k8s.io/minikube/pkg/minikube/sshutil"
+)
+
+var (
+	appendKnown bool
 )
 
 // sshHostCmd represents the sshHostCmd command
@@ -65,10 +72,45 @@ var sshHostCmd = &cobra.Command{
 			os.Exit(1)
 		}
 
+		if appendKnown {
+			addr, port, err := machine.GetSSHHostAddrPort(co.API, *co.Config, *n)
+			if err != nil {
+				out.ErrLn("GetSSHHostAddrPort: %v", err)
+				os.Exit(1)
+			}
+
+			host := addr
+			if port != 22 {
+				host = fmt.Sprintf("[%s]:%d", addr, port)
+			}
+			knownHosts := filepath.Join(homedir.HomeDir(), ".ssh", "known_hosts")
+
+			fmt.Fprintf(os.Stderr, "Host added: %s (%s)\n", knownHosts, host)
+			if sshutil.KnownHost(host, knownHosts) {
+				return
+			}
+
+			f, err := os.OpenFile(knownHosts, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0600)
+			if err != nil {
+				out.ErrLn("OpenFile: %v", err)
+				os.Exit(1)
+			}
+			defer f.Close()
+
+			_, err = f.WriteString(keys)
+			if err != nil {
+				out.ErrLn("WriteString: %v", err)
+				os.Exit(1)
+			}
+
+			return
+		}
+
 		fmt.Printf("%s", keys)
 	},
 }
 
 func init() {
 	sshHostCmd.Flags().StringVarP(&nodeName, "node", "n", "", "The node to ssh into. Defaults to the primary control plane.")
+	sshHostCmd.Flags().BoolVar(&appendKnown, "append-known", false, "Add host key to SSH known_hosts file")
 }

pkg/minikube/machine/ssh.go

@@ -69,31 +69,39 @@ func CreateSSHShell(api libmachine.API, cc config.ClusterConfig, n config.Node,
 	return client.Shell(args...)
 }
 
-// RunSSHHostCommand runs a command to the SSH host
-func RunSSHHostCommand(api libmachine.API, cc config.ClusterConfig, n config.Node, command string, args []string) (string, error) {
+func GetSSHHostAddrPort(api libmachine.API, cc config.ClusterConfig, n config.Node) (string, int, error) {
 	host, err := getHost(api, cc, n)
 	if err != nil {
-		return "", err
+		return "", 0, err
 	}
 
-	cmdPath, err := exec.LookPath(command)
+	addr, err := host.Driver.GetSSHHostname()
 	if err != nil {
-		return "", err
+		return "", 0, err
 	}
-
 	port, err := host.Driver.GetSSHPort()
 	if err != nil {
-		return "", err
+		return "", 0, err
 	}
 
-	args = append(args, "-p")
-	args = append(args, fmt.Sprintf("%d", port))
+	return addr, port, nil
+}
 
-	addr, err := host.Driver.GetSSHHostname()
+// RunSSHHostCommand runs a command to the SSH host
+func RunSSHHostCommand(api libmachine.API, cc config.ClusterConfig, n config.Node, command string, args []string) (string, error) {
+	addr, port, err := GetSSHHostAddrPort(api, cc, n)
 	if err != nil {
 		return "", err
 	}
 
+	cmdPath, err := exec.LookPath(command)
+	if err != nil {
+		return "", err
+	}
+
+	args = append(args, "-p")
+	args = append(args, fmt.Sprintf("%d", port))
+
 	args = append(args, addr)
 
 	cmd := exec.Command(cmdPath, args...)

pkg/minikube/sshutil/sshutil.go

@@ -17,14 +17,17 @@ limitations under the License.
 package sshutil
 
 import (
+	"bufio"
 	"net"
+	"os"
 	"strconv"
 	"time"
 
 	"github.com/docker/machine/libmachine/drivers"
 	machinessh "github.com/docker/machine/libmachine/ssh"
 	"github.com/pkg/errors"
 	"golang.org/x/crypto/ssh"
+	"golang.org/x/crypto/ssh/knownhosts"
 	"k8s.io/klog/v2"
 
 	"k8s.io/minikube/pkg/util/retry"
@@ -89,3 +92,28 @@ func newSSHHost(d drivers.Driver) (*sshHost, error) {
 		Username:   d.GetSSHUsername(),
 	}, nil
 }
+
+func KnownHost(host string, knownHosts string) bool {
+	fd, err := os.Open(knownHosts)
+	if err != nil {
+		return false
+	}
+	defer fd.Close()
+
+	hashhost := knownhosts.HashHostname(host)
+	scanner := bufio.NewScanner(fd)
+	for scanner.Scan() {
+		_, hosts, _, _, _, err := ssh.ParseKnownHosts(scanner.Bytes())
+		if err != nil {
+			continue
+		}
+
+		for _, h := range hosts {
+			if h == host || h == hashhost {
+				return true
+			}
+		}
+	}
+
+	return false
+}

site/content/en/docs/commands/ssh-host.md

@@ -20,7 +20,8 @@ minikube ssh-host [flags]
 ### Options
 
 ```
-  -n, --node string   The node to ssh into. Defaults to the primary control plane.
+      --append-known   Add host key to SSH known_hosts file
+  -n, --node string    The node to ssh into. Defaults to the primary control plane.
 ```
 
 ### Options inherited from parent commands