Plain mode: support port forwarding

Signed-off-by: Praful Khanduri <holiodin@gmail.com>

Author: Horiodino

cmd/limactl/editflags/editflags.go

@@ -96,6 +96,11 @@ func RegisterCreate(cmd *cobra.Command, commentPrefix string) {
 	})
 
 	flags.Bool("plain", false, commentPrefix+"Plain mode. Disables mounts, port forwarding, containerd, etc.")
+
+	flags.StringSlice("port-forward", nil, commentPrefix+"Port forwards (host:guest), works even in plain mode, e.g., '8080:80,2222:22'")
+	_ = cmd.RegisterFlagCompletionFunc("port-forward", func(*cobra.Command, []string, string) ([]string, cobra.ShellCompDirective) {
+		return []string{"8080:80", "2222:22", "3000:3000"}, cobra.ShellCompDirectiveNoFileComp
+	})
 }
 
 func defaultExprFunc(expr string) func(v *flag.Flag) (string, error) {
@@ -206,6 +211,7 @@ func YQExpressions(flags *flag.FlagSet, newInstance bool) ([]string, error) {
 			false,
 			false,
 		},
+
 		{
 			"rosetta",
 			func(_ *flag.Flag) (string, error) {
@@ -261,6 +267,36 @@ func YQExpressions(flags *flag.FlagSet, newInstance bool) ([]string, error) {
 		{"disk", d(".disk= \"%sGiB\""), false, false},
 		{"vm-type", d(".vmType = %q"), true, false},
 		{"plain", d(".plain = %s"), true, false},
+		{
+			"port-forward",
+			func(_ *flag.Flag) (string, error) {
+				ss, err := flags.GetStringSlice("port-forward")
+				if err != nil {
+					return "", err
+				}
+				if len(ss) == 0 {
+					return "", nil
+				}
+
+				expr := `.portForwards = [`
+				for i, s := range ss {
+					parts := strings.Split(s, ":")
+					if len(parts) != 2 {
+						return "", fmt.Errorf("invalid port forward format %q, expected HOST:GUEST", s)
+					}
+					hostPort := strings.TrimSpace(parts[0])
+					guestPort := strings.TrimSpace(parts[1])
+					expr += fmt.Sprintf(`{"hostPort": %s, "guestPort": %s}`, hostPort, guestPort)
+					if i < len(ss)-1 {
+						expr += ","
+					}
+				}
+				expr += `]`
+				return expr, nil
+			},
+			false,
+			false,
+		},
 	}
 	var exprs []string
 	for _, def := range defs {

pkg/hostagent/hostagent.go

@@ -420,7 +420,11 @@ func (a *HostAgent) Info(_ context.Context) (*hostagentapi.Info, error) {
 
 func (a *HostAgent) startHostAgentRoutines(ctx context.Context) error {
 	if *a.instConfig.Plain {
-		logrus.Info("Running in plain mode. Mounts, port forwarding, containerd, etc. will be ignored. Guest agent will not be running.")
+		if len(a.instConfig.PortForwards) > 0 {
+			logrus.Info("Running in plain mode. Mounts, containerd, etc. will be ignored. Guest agent will not be running. Port forwarding is enabled via static SSH tunnels.")
+		} else {
+			logrus.Info("Running in plain mode. Mounts, port forwarding, containerd, etc. will be ignored. Guest agent will not be running.")
+		}
 	}
 	a.onClose = append(a.onClose, func() error {
 		logrus.Debugf("shutting down the SSH master")
@@ -478,7 +482,7 @@ sudo chown -R "${USER}" /run/host-services`
 			return errors.Join(unlockErrs...)
 		})
 	}
-	if !*a.instConfig.Plain {
+	if !*a.instConfig.Plain || len(a.instConfig.PortForwards) > 0 && *a.instConfig.Plain {
 		go a.watchGuestAgentEvents(ctx)
 	}
 	if err := a.waitForRequirements("optional", a.optionalRequirements()); err != nil {
@@ -543,6 +547,26 @@ func (a *HostAgent) watchGuestAgentEvents(ctx context.Context) {
 		}
 	}
 
+	if *a.instConfig.Plain {
+		logrus.Debugf("Setting up static TCP port forwarding for plain mode")
+		for _, rule := range a.instConfig.PortForwards {
+			if rule.GuestSocket == "" {
+				guest := &guestagentapi.IPPort{
+					Ip:       rule.GuestIP.String(),
+					Port:     int32(rule.GuestPort),
+					Protocol: string(rule.Proto),
+				}
+				local, remote := a.portForwarder.forwardingAddresses(guest)
+				if local != "" {
+					logrus.Infof("Setting up static TCP forwarding from %s to %s", remote, local)
+					if err := forwardTCP(ctx, a.sshConfig, a.sshLocalPort, local, remote, verbForward); err != nil {
+						logrus.WithError(err).Warnf("failed to set up static TCP forwarding %s -> %s", remote, local)
+					}
+				}
+			}
+		}
+	}
+
 	localUnix := filepath.Join(a.instDir, filenames.GuestAgentSock)
 	remoteUnix := "/run/lima-guestagent.sock"
 

pkg/limayaml/defaults.go

@@ -916,7 +916,6 @@ func fixUpForPlainMode(y *LimaYAML) {
 		return
 	}
 	y.Mounts = nil
-	y.PortForwards = nil
 	y.Containerd.System = ptr.Of(false)
 	y.Containerd.User = ptr.Of(false)
 	y.Rosetta.BinFmt = ptr.Of(false)

pkg/limayaml/validate.go

@@ -415,6 +415,16 @@ func Validate(y *LimaYAML, warn bool) error {
 			}
 		}
 	}
+	if y.Plain != nil && *y.Plain {
+		const portRangeWarnThreshold = 10
+		for i, rule := range y.PortForwards {
+			guestRange := rule.GuestPortRange[1] - rule.GuestPortRange[0] + 1
+			hostRange := rule.HostPortRange[1] - rule.HostPortRange[0] + 1
+			if guestRange > portRangeWarnThreshold || hostRange > portRangeWarnThreshold {
+				logrus.Warnf("[plain mode] portForwards[%d] covers a range of more than %d ports (guest: %d, host: %d). All ports will be forwarded unconditionally, which may be inefficient.", i, portRangeWarnThreshold, guestRange, hostRange)
+			}
+		}
+	}
 
 	return errs
 }

templates/default.yaml

@@ -422,7 +422,7 @@ networks:
 
 # Port forwarding rules. Forwarding between ports 22 and ssh.localPort cannot be overridden.
 # Rules are checked sequentially until the first one matches.
-# portForwards:
+portForwards: null
 # - guestPort: 443
 #   hostIP: "0.0.0.0" # overrides the default value "127.0.0.1"; allows privileged port forwarding
 # # default: hostPort: 443 (same as guestPort)
@@ -613,4 +613,4 @@ nestedVirtualization: null
 
 # ===================================================================== #
 # END OF TEMPLATE
-# ===================================================================== #
+# ===================================================================== #