Allowing generic driver to use ssh-agent to get identities

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

docs/drivers/generic.md

@@ -33,9 +33,20 @@ Options:
 
 Environment variables and default values:
 
-| CLI option                 | Environment variable | Default             |
-| -------------------------- | -------------------- | ------------------- |
-| **`--generic-ip-address`** | `GENERIC_IP_ADDRESS` | -                   |
-| `--generic-ssh-key`        | `GENERIC_SSH_KEY`    | `$HOME/.ssh/id_rsa` |
-| `--generic-ssh-user`       | `GENERIC_SSH_USER`   | `root`              |
-| `--generic-ssh-port`       | `GENERIC_SSH_PORT`   | `22`                |
+| CLI option                 | Environment variable | Default                   |
+|----------------------------|----------------------|---------------------------|
+| **`--generic-ip-address`** | `GENERIC_IP_ADDRESS` | -                         |
+| `--generic-ssh-key`        | `GENERIC_SSH_KEY`    | _(defers to `ssh-agent`)_ |
+| `--generic-ssh-user`       | `GENERIC_SSH_USER`   | `root`                    |
+| `--generic-ssh-port`       | `GENERIC_SSH_PORT`   | `22`                      |
+
+##### Interaction with SSH Agents
+
+When an SSH identity is not provided (with the `--generic-ssh-key` flag),
+the SSH agent (if running) will be consulted. This makes it possible to
+easily use password-protected SSH keys.
+
+Note that this usage is _only_ supported if you're using the external SSH client,
+which is the default behaviour when the `ssh` binary is available. If you're
+using the native client (with `--native-ssh`), using the SSH agent is not yet
+supported.

drivers/generic/generic.go

@@ -5,7 +5,6 @@ import (
 	"fmt"
 	"net"
 	"os"
-	"path/filepath"
 	"strconv"
 	"time"
 
@@ -25,10 +24,6 @@ const (
 	defaultTimeout = 1 * time.Second
 )
 
-var (
-	defaultSourceSSHKey = filepath.Join(mcnutils.GetHomeDir(), ".ssh", "id_rsa")
-)
-
 // GetCreateFlags registers the flags this driver adds to
 // "docker hosts create"
 func (d *Driver) GetCreateFlags() []mcnflag.Flag {
@@ -46,8 +41,8 @@ func (d *Driver) GetCreateFlags() []mcnflag.Flag {
 		},
 		mcnflag.StringFlag{
 			Name:   "generic-ssh-key",
-			Usage:  "SSH private key path",
-			Value:  defaultSourceSSHKey,
+			Usage:  "SSH private key path (if not provided, identities in ssh-agent will be used)",
+			Value:  "",
 			EnvVar: "GENERIC_SSH_KEY",
 		},
 		mcnflag.IntFlag{
@@ -66,7 +61,6 @@ func NewDriver(hostName, storePath string) drivers.Driver {
 			MachineName: hostName,
 			StorePath:   storePath,
 		},
-		SSHKey: defaultSourceSSHKey,
 	}
 }
 
@@ -83,6 +77,17 @@ func (d *Driver) GetSSHUsername() string {
 	return d.SSHUser
 }
 
+func (d *Driver) GetSSHKeyPath() string {
+	if d.SSHKey == "" {
+		return ""
+	}
+
+	if d.SSHKeyPath == "" {
+		d.SSHKeyPath = d.ResolveStorePath("id_rsa")
+	}
+	return d.SSHKeyPath
+}
+
 func (d *Driver) SetConfigFromFlags(flags drivers.DriverOptions) error {
 	d.IPAddress = flags.String("generic-ip-address")
 	d.SSHUser = flags.String("generic-ssh-user")
@@ -93,31 +98,33 @@ func (d *Driver) SetConfigFromFlags(flags drivers.DriverOptions) error {
 		return errors.New("generic driver requires the --generic-ip-address option")
 	}
 
-	if d.SSHKey == "" {
-		return errors.New("generic driver requires the --generic-ssh-key option")
-	}
-
 	return nil
 }
 
 func (d *Driver) PreCreateCheck() error {
-	if _, err := os.Stat(d.SSHKey); os.IsNotExist(err) {
-		return fmt.Errorf("Ssh key does not exist: %q", d.SSHKey)
+	if d.SSHKey != "" {
+		if _, err := os.Stat(d.SSHKey); os.IsNotExist(err) {
+			return fmt.Errorf("Ssh key does not exist: %q", d.SSHKey)
+		}
 	}
 
 	return nil
 }
 
 func (d *Driver) Create() error {
-	log.Info("Importing SSH key...")
+	if d.SSHKey == "" {
+		log.Info("No SSH key specified. Connecting to this machine now and in the" +
+			" future will require the ssh agent to contain the appropriate key.")
+	} else {
+		log.Info("Importing SSH key...")
+		// TODO: validate the key is a valid key
+		if err := mcnutils.CopyFile(d.SSHKey, d.GetSSHKeyPath()); err != nil {
+			return fmt.Errorf("unable to copy ssh key: %s", err)
+		}
 
-	// TODO: validate the key is a valid key
-	if err := mcnutils.CopyFile(d.SSHKey, d.GetSSHKeyPath()); err != nil {
-		return fmt.Errorf("unable to copy ssh key: %s", err)
-	}
-
-	if err := os.Chmod(d.GetSSHKeyPath(), 0600); err != nil {
-		return fmt.Errorf("unable to set permissions on the ssh key: %s", err)
+		if err := os.Chmod(d.GetSSHKeyPath(), 0600); err != nil {
+			return fmt.Errorf("unable to set permissions on the ssh key: %s", err)
+		}
 	}
 
 	log.Debugf("IP: %s", d.IPAddress)

libmachine/drivers/utils.go

@@ -19,8 +19,13 @@ func GetSSHClientFromDriver(d Driver) (ssh.Client, error) {
 		return nil, err
 	}
 
-	auth := &ssh.Auth{
-		Keys: []string{d.GetSSHKeyPath()},
+	var auth *ssh.Auth
+	if d.GetSSHKeyPath() == "" {
+		auth = &ssh.Auth{}
+	} else {
+		auth = &ssh.Auth{
+			Keys: []string{d.GetSSHKeyPath()},
+		}
 	}
 
 	client, err := ssh.NewClient(d.GetSSHUsername(), address, port, auth)

libmachine/host/host.go

@@ -69,8 +69,13 @@ func (h *Host) CreateSSHClient() (ssh.Client, error) {
 		return ssh.ExternalClient{}, err
 	}
 
-	auth := &ssh.Auth{
-		Keys: []string{h.Driver.GetSSHKeyPath()},
+	var auth *ssh.Auth
+	if h.Driver.GetSSHKeyPath() == "" {
+		auth = &ssh.Auth{}
+	} else {
+		auth = &ssh.Auth{
+			Keys: []string{h.Driver.GetSSHKeyPath()},
+		}
 	}
 
 	return ssh.NewClient(h.Driver.GetSSHUsername(), addr, port, auth)

libmachine/ssh/client.go

@@ -49,7 +49,6 @@ const (
 var (
 	baseSSHArgs = []string{
 		"-o", "PasswordAuthentication=no",
-		"-o", "IdentitiesOnly=yes",
 		"-o", "StrictHostKeyChecking=no",
 		"-o", "UserKnownHostsFile=/dev/null",
 		"-o", "LogLevel=quiet", // suppress "Warning: Permanently added '[localhost]:2022' (ECDSA) to the list of known hosts."
@@ -262,9 +261,17 @@ func NewExternalClient(sshBinaryPath, user, host string, port int, auth *Auth) (
 
 	args := append(baseSSHArgs, fmt.Sprintf("%s@%s", user, host))
 
+	// If no identities are explicitly provided, also look at the identities
+	// offered by ssh-agent
+	if len(auth.Keys) > 0 {
+		args = append(args, "-o", "IdentitiesOnly=yes")
+	}
+
 	// Specify which private keys to use to authorize the SSH request.
 	for _, privateKeyPath := range auth.Keys {
-		args = append(args, "-i", privateKeyPath)
+		if privateKeyPath != "" {
+			args = append(args, "-i", privateKeyPath)
+		}
 	}
 
 	// Set which port to use for SSH.