BREAKING CHANGE: move Uncloud API socket to /run/uncloud/api/uncloud.sock, activate it by systemd socket unit

README.md

@@ -166,7 +166,9 @@ $ uc machine init --name oracle-vm ubuntu@152.67.101.197
 ✓ uncloudd binary installed: /usr/local/bin/uncloudd
 ⏳ Downloading uninstall script: https://raw.githubusercontent.com/psviderski/uncloud/refs/heads/main/scripts/uninstall.sh
 ✓ uncloud-uninstall script installed: /usr/local/bin/uncloud-uninstall
+✓ Systemd unit file created: /etc/systemd/system/uncloud.socket
 ✓ Systemd unit file created: /etc/systemd/system/uncloud.service
+Created symlink /etc/systemd/system/sockets.target.wants/uncloud.socket → /etc/systemd/system/uncloud.socket.
 Created symlink /etc/systemd/system/multi-user.target.wants/uncloud.service → /etc/systemd/system/uncloud.service.
 ⏳ Starting Uncloud machine daemon (uncloud.service)...
 ✓ Uncloud machine daemon started.
@@ -208,7 +210,9 @@ $ uc machine add --name hetzner-server root@5.223.45.199
 ✓ uncloudd binary installed: /usr/local/bin/uncloudd
 ⏳ Downloading uninstall script: https://raw.githubusercontent.com/psviderski/uncloud/refs/heads/main/scripts/uninstall.sh
 ✓ uncloud-uninstall script installed: /usr/local/bin/uncloud-uninstall
+✓ Systemd unit file created: /etc/systemd/system/uncloud.socket
 ✓ Systemd unit file created: /etc/systemd/system/uncloud.service
+Created symlink /etc/systemd/system/sockets.target.wants/uncloud.socket → /etc/systemd/system/uncloud.socket.
 Created symlink /etc/systemd/system/multi-user.target.wants/uncloud.service → /etc/systemd/system/uncloud.service.
 ⏳ Starting Uncloud machine daemon (uncloud.service)...
 ✓ Uncloud machine daemon started.
@@ -319,9 +323,9 @@ I'm grateful to the following projects that inspired Uncloud's design and implem
 * [Tailscale](https://tailscale.com/) — for pioneering the vision of decentralised flat mesh networking with an amazing
   user experience that feels like magic.
 * [Talos Linux](https://github.com/siderolabs/talos)
-  and [KubeSpan](https://www.talos.dev/v1.10/talos-guides/network/kubespan/) — for the machine API design using
-  [grpc-proxy](https://github.com/siderolabs/grpc-proxy) and for its elegant approach to secure WireGuard-based overlay
-  networking with zero configuration.
+  and [KubeSpan](https://www.talos.dev/v1.10/talos-guides/network/kubespan/) — for inspiring Uncloud's API routing
+  design with [grpc-proxy](https://github.com/siderolabs/grpc-proxy) and for their elegant approach to secure
+  WireGuard-based overlay networking with zero configuration.
 * [Docker Swarm Classic](https://github.com/docker-archive/classicswarm) and
   [Rancher 1.x](http://rancher-com-website-main-elb-elb-1798790864.us-west-2.elb.amazonaws.com/docs/rancher/v1.6/en/)
   — for showing the power of simplicity and pragmatism in container orchestration and that not every problem needs the

caddystorage/module.go

@@ -22,7 +22,7 @@ const (
 	// ModuleID is the Caddy module ID for Uncloud storage.
 	ModuleID = "caddy.storage.uncloud"
 	// DefaultSocketPath is the default path to the Uncloud API socket.
-	DefaultSocketPath = "/run/uncloud/uncloud.sock"
+	DefaultSocketPath = "/run/uncloud/api/uncloud.sock"
 	// DefaultLockTTL is the default duration of a distributed lock lease.
 	DefaultLockTTL = 20 * time.Second
 	// lockCleanupTimeout bounds how long an unloaded module waits for active lock operations when cleaning up.
@@ -37,7 +37,7 @@ func init() {
 // Storage implements a Caddy storage backend that uses an Uncloud cluster to store assets such as TLS certificates.
 type Storage struct {
 	// Socket is the path to the Uncloud API socket.
-	// Defaults to /run/uncloud/uncloud.sock when not set.
+	// Defaults to /run/uncloud/api/uncloud.sock when not set.
 	Socket string `json:"socket,omitempty"`
 	// LockTTL is the duration of a distributed lock after which it expires if not renewed. Locks renew automatically
 	// until unlocked. If an instance crashes or cannot renew, expiry allows another instance to acquire the stale lock.
@@ -154,7 +154,7 @@ func (s *Storage) CertMagicStorage() (certmagic.Storage, error) {
 //
 //	{
 //	    storage uncloud {
-//	        socket /run/uncloud/uncloud.sock
+//	        socket /run/uncloud/api/uncloud.sock
 //	        lock_ttl 20s
 //	    }
 //	}

cmd/uc/machine/add.go

@@ -192,7 +192,7 @@ func add(ctx context.Context, uncli *cli.CLI, remoteMachine *cli.RemoteMachine,
 	// Deploy a Caddy service container to the added machine. If caddy service is already deployed on other machines,
 	// use the deployed image version.
 	// NOTE: We use the cluster client to inspect and scale the Caddy service because the newly added machine may have
-	// issues accessing the Machine API of existing machines in the cluster.
+	// issues accessing the API of existing machines in the cluster.
 	// See the issue for more details: https://github.com/psviderski/uncloud/issues/65.
 	caddyImage := ""
 	caddySvc, err := clusterClient.InspectService(ctx, client.CaddyServiceName)

cmd/uc/main.go

@@ -88,10 +88,11 @@ func main() {
 
 			configPath := fs.ExpandHomeDir(opts.configPath)
 
+			// Make uc connect via the local Unix socket when running on a cluster machine.
 			if opts.connect == "" {
-				if !fs.Exists(configPath) && fs.Exists(machine.DefaultUncloudSockPath) {
+				if !fs.Exists(configPath) && fs.Exists(machine.DefaultClusterAPISockPath) {
 					conn = &config.MachineConnection{
-						Unix: machine.DefaultUncloudSockPath,
+						Unix: machine.DefaultClusterAPISockPath,
 					}
 				}
 			}

cmd/uncloudd/dialstdio.go

@@ -23,7 +23,7 @@ func newDialStdioCommand() *cobra.Command {
 		},
 	}
 
-	cmd.Flags().StringVar(&socketPath, "socket", machine.DefaultUncloudSockPath,
+	cmd.Flags().StringVar(&socketPath, "socket", machine.DefaultClusterAPISockPath,
 		"Path to the Uncloud API socket")
 
 	return cmd

experiment/wg/connector.go

@@ -60,7 +60,7 @@ func (c *WireGuardConnector) Connect(ctx context.Context) (*grpc.ClientConn, err
 	}
 	endpoint := netip.AddrPortFrom(endpointAddr, DefaultEndpointPort)
 	machineManagementIP := network.ManagementIP(machine.PublicKey)
-	machineAPIAddr := net.JoinHostPort(machineManagementIP.String(), strconv.Itoa(constants.MachineAPIPort))
+	machineAPIAddr := net.JoinHostPort(machineManagementIP.String(), strconv.Itoa(constants.UncloudAPIPort))
 
 	tunCfg := &Config{
 		LocalAddress:    c.user.ManagementIP(),

internal/cli/cli.go

@@ -603,7 +603,7 @@ func provisionOrConnectRemoteMachine(
 		if remoteMachine.User != rootUser {
 			// provisionMachine has just added the user to the uncloud group. Any SSH ControlMaster left over from
 			// a previous uc invocation (e.g. a failed uc command against the uninitialised machine) still holds
-			// the old user groups and would deny access to /run/uncloud/uncloud.sock. Close the current session
+			// the old user groups and would deny access to /run/uncloud/api/uncloud.sock. Close the current session
 			// if it exists so the next session picks up the new groups.
 			conn.CloseControlMaster(ctx)
 		}

internal/cli/config/connection_test.go

@@ -70,9 +70,9 @@ func TestMachineConnection_String(t *testing.T) {
 		{
 			name: "unix connection",
 			conn: MachineConnection{
-				Unix: "/run/uncloud/uncloud.sock",
+				Unix: "/run/uncloud/api/uncloud.sock",
 			},
-			want: "unix:///run/uncloud/uncloud.sock",
+			want: "unix:///run/uncloud/api/uncloud.sock",
 		},
 		{
 			name: "no connection",

internal/daemon/daemon.go

@@ -2,24 +2,50 @@ package daemon
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log/slog"
+	"net"
 
+	"github.com/coreos/go-systemd/activation"
 	systemd "github.com/coreos/go-systemd/daemon"
 	"github.com/psviderski/uncloud/internal/machine"
 )
 
+const systemdSocketUnit = "uncloud.socket"
+
 type Daemon struct {
 	machine *machine.Machine
 }
 
 func New(dataDir string) (*Daemon, error) {
+	listeners, err := activation.ListenersWithNames()
+	if err != nil {
+		return nil, fmt.Errorf("get systemd-activated sockets: %w", err)
+	}
+
+	listener, err := selectActivatedListener(listeners)
+	if err != nil {
+		return nil, err
+	}
+	if listener != nil {
+		slog.Info("Using systemd-activated API socket.", "addr", listener.Addr().String())
+	}
+
 	config := &machine.Config{
-		DataDir: dataDir,
+		DataDir:            dataDir,
+		ClusterAPISockPath: machine.DefaultClusterAPISockPath,
+		ClusterAPIListener: listener,
 	}
 	mach, err := machine.NewMachine(config)
 	if err != nil {
-		return nil, fmt.Errorf("init machine: %w", err)
+		initErr := fmt.Errorf("init machine: %w", err)
+		if listener != nil {
+			if closeErr := listener.Close(); closeErr != nil {
+				initErr = errors.Join(initErr, fmt.Errorf("close systemd-activated socket: %w", closeErr))
+			}
+		}
+		return nil, initErr
 	}
 
 	return &Daemon{
@@ -27,6 +53,40 @@ func New(dataDir string) (*Daemon, error) {
 	}, nil
 }
 
+// selectActivatedListener returns the systemd activated listener. If systemd supplied multiple listeners,
+// it returns the one associated with systemdSocketUnit.
+func selectActivatedListener(listeners map[string][]net.Listener) (net.Listener, error) {
+	var activated []net.Listener
+	for _, named := range listeners {
+		activated = append(activated, named...)
+	}
+
+	if len(activated) == 0 {
+		return nil, nil
+	}
+	if len(activated) == 1 {
+		return activated[0], nil
+	}
+
+	named, ok := listeners[systemdSocketUnit]
+	if !ok || len(named) != 1 {
+		return nil, fmt.Errorf("expected one systemd-activated socket named '%s', received %d",
+			systemdSocketUnit, len(named))
+	}
+
+	// Close all other unused listeners.
+	for name, unused := range listeners {
+		if name == systemdSocketUnit {
+			continue
+		}
+		for _, l := range unused {
+			_ = l.Close()
+		}
+	}
+
+	return named[0], nil
+}
+
 func (d *Daemon) Run(ctx context.Context) error {
 	slog.Info("Starting machine.")
 

internal/daemon/daemon_test.go

@@ -0,0 +1,71 @@
+package daemon
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSelectActivatedListener(t *testing.T) {
+	t.Run("no activated listeners", func(t *testing.T) {
+		listener, err := selectActivatedListener(nil)
+		require.NoError(t, err)
+		assert.Nil(t, listener)
+	})
+
+	t.Run("only listener regardless of name", func(t *testing.T) {
+		activated := testListener(t)
+
+		listener, err := selectActivatedListener(map[string][]net.Listener{"another.socket": {activated}})
+		require.NoError(t, err)
+		assert.Same(t, activated, listener)
+	})
+
+	t.Run("named listener when multiple", func(t *testing.T) {
+		activated := testListener(t)
+		extra := testListener(t)
+
+		listener, err := selectActivatedListener(map[string][]net.Listener{
+			systemdSocketUnit: {activated},
+			"another.socket":  {extra},
+		})
+		require.NoError(t, err)
+		assert.Same(t, activated, listener)
+		assert.Error(t, extra.Close())
+	})
+
+	t.Run("multiple listeners without expected name", func(t *testing.T) {
+		first := testListener(t)
+		second := testListener(t)
+
+		listener, err := selectActivatedListener(map[string][]net.Listener{
+			"first.socket":  {first},
+			"second.socket": {second},
+		})
+		require.ErrorContains(t, err, "expected one systemd-activated socket")
+		assert.Nil(t, listener)
+	})
+
+	t.Run("multiple listeners under expected name", func(t *testing.T) {
+		first := testListener(t)
+		second := testListener(t)
+
+		listener, err := selectActivatedListener(map[string][]net.Listener{
+			systemdSocketUnit: {first, second},
+		})
+		require.ErrorContains(t, err, "expected one systemd-activated socket")
+		assert.Nil(t, listener)
+	})
+}
+
+func testListener(t *testing.T) net.Listener {
+	t.Helper()
+
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = listener.Close() })
+
+	return listener
+}

internal/machine/cluster.go

@@ -176,7 +176,7 @@ func (cc *clusterController) Run(ctx context.Context) error {
 	// Start the network API server before waiting for the store sync so the machine is reachable on the mesh
 	// during the sync and can serve requests that don't depend on the store.
 	// Assume the management IP can't be changed when the network is running.
-	apiAddr := net.JoinHostPort(cc.state.Network.ManagementIP.String(), strconv.Itoa(constants.MachineAPIPort))
+	apiAddr := net.JoinHostPort(cc.state.Network.ManagementIP.String(), strconv.Itoa(constants.UncloudAPIPort))
 	listener, err := net.Listen("tcp", apiAddr)
 	if err != nil {
 		return fmt.Errorf("listen API port: %w", err)

internal/machine/constants/constants.go

@@ -1,8 +1,9 @@
 package constants
 
 const (
-	// MachineAPIPort is the port for the Machine API service on the management WireGuard network.
-	MachineAPIPort = 51000
-	// UnregistryPort is the port for the embedded container registry listening on the machine IP.
+	// UncloudAPIPort is the TCP port on which each machine serves the Uncloud API over the management WireGuard
+	// network.
+	UncloudAPIPort = 51000
+	// UnregistryPort is the TCP port for the embedded container registry listening on the machine IP.
 	UnregistryPort = 51500
 )

internal/machine/firewall/iptables_linux.go

@@ -48,12 +48,12 @@ func ConfigureIptablesChains(machineIP netip.Addr, wgPort int) error {
 		}
 	}
 
-	// Allow cluster machines to access Machine API via the management IPv6 WireGuard network.
+	// Allow cluster machines to access the Uncloud API via the management IPv6 WireGuard network.
 	acceptMachineAPIRule := []string{
 		"-i", network.WireGuardInterfaceName,
 		"-s", "fdcc::/16",
 		"-p", "tcp",
-		"--dport", strconv.Itoa(constants.MachineAPIPort),
+		"--dport", strconv.Itoa(constants.UncloudAPIPort),
 		"-j", "ACCEPT",
 	}
 	// Allow Corrosion gossip traffic from cluster machines via the management IPv6 WireGuard network.

internal/machine/machine.go

@@ -58,9 +58,13 @@ import (
 )
 
 const (
-	DefaultMachineSockPath = "/run/uncloud/machine.sock"
-	DefaultUncloudSockPath = "/run/uncloud/uncloud.sock"
-	DefaultSockGroup       = "uncloud"
+	// DefaultMachineAPISockPath is the default path to the Unix socket for API requests handled directly by this
+	// machine.
+	DefaultMachineAPISockPath = "/run/uncloud/machine.sock"
+	// DefaultClusterAPISockPath is the default path to the Unix socket for the client-facing API that routes requests
+	// across the cluster.
+	DefaultClusterAPISockPath = "/run/uncloud/api/uncloud.sock"
+	DefaultSockGroup          = "uncloud"
 	// DefaultCaddyAdminSockPath is the default path to the Caddy admin socket for validating the generated Caddy
 	// reverse proxy configuration.
 	DefaultCaddyAdminSockPath = "/run/uncloud/caddy/admin.sock"
@@ -70,9 +74,15 @@ const (
 
 type Config struct {
 	// DataDir is the directory where the machine stores its persistent state. Default is /var/lib/uncloud.
-	DataDir         string
-	MachineSockPath string
-	UncloudSockPath string
+	DataDir string
+	// MachineAPISockPath is the path to the Unix socket for API requests handled directly by this machine.
+	MachineAPISockPath string
+	// ClusterAPISockPath is the path to the Unix socket for the client-facing API that routes requests across the
+	// cluster.
+	ClusterAPISockPath string
+	// ClusterAPIListener is an optional pre-bound listener for the client-facing API that routes requests across the
+	// cluster. If set, Run takes ownership of it and closes it on shutdown or startup failure.
+	ClusterAPIListener net.Listener
 
 	CorrosionDataDir string
 	// CorrosionRunDir is the runtime directory for the corrosion service.
@@ -104,11 +114,11 @@ func (c *Config) SetDefaults() (*Config, error) {
 	if cfg.DataDir == "" {
 		cfg.DataDir = "/var/lib/uncloud"
 	}
-	if cfg.MachineSockPath == "" {
-		cfg.MachineSockPath = DefaultMachineSockPath
+	if cfg.MachineAPISockPath == "" {
+		cfg.MachineAPISockPath = DefaultMachineAPISockPath
 	}
-	if cfg.UncloudSockPath == "" {
-		cfg.UncloudSockPath = DefaultUncloudSockPath
+	if cfg.ClusterAPISockPath == "" && cfg.ClusterAPIListener == nil {
+		cfg.ClusterAPISockPath = DefaultClusterAPISockPath
 	}
 
 	if cfg.DockerClient == nil {
@@ -165,7 +175,7 @@ type Machine struct {
 
 	config Config
 	state  *State
-	// started is closed when the machine is ready to serve requests on the local API server.
+	// started is closed when the machine and cluster API servers are ready to serve requests.
 	started chan struct{}
 	// initialised is closed when the machine is configured as a member of a cluster.
 	initialised chan struct{}
@@ -186,15 +196,14 @@ type Machine struct {
 	// dockerService provides high-level operations for managing Docker containers.
 	dockerService *machinedocker.Service
 	dockerServer  *machinedocker.Server
-	// localMachineServer is the gRPC server for the machine API listening on the local Unix socket.
-	localMachineServer *grpc.Server
+	// machineAPIServer handles API requests directly on this machine.
+	machineAPIServer *grpc.Server
 
-	// proxyDirector manages routing of gRPC requests between local and remote machine API servers.
+	// proxyDirector routes API requests to local or remote machines.
 	proxyDirector *apiproxy.Director
-	// localProxyServer is the gRPC proxy server for the machine API listening on the local Unix socket.
-	// It proxies requests to the local or remote machine API servers depending on the request targets
-	// and aggregates responses.
-	localProxyServer *grpc.Server
+	// clusterAPIServer is the client-facing gRPC server that routes API requests across the cluster. It sends requests
+	// to one or more local or remote machines and aggregates their responses.
+	clusterAPIServer *grpc.Server
 
 	// mu protects the Machine from concurrent reads and writes.
 	mu sync.RWMutex
@@ -269,10 +278,10 @@ func NewMachine(config *Config) (*Machine, error) {
 	}
 	dockerService := machinedocker.NewService(config.DockerClient, db)
 
-	// Init a local gRPC proxy server that proxies requests to the local or remote machine API servers.
+	// Init the client-facing API server that routes requests to local or remote machines.
 	mapper := apiproxy.NewCorrosionMapper(corroStore)
-	proxyDirector := apiproxy.NewDirector(config.MachineSockPath, constants.MachineAPIPort, mapper)
-	localProxyServer := grpc.NewServer(
+	proxyDirector := apiproxy.NewDirector(config.MachineAPISockPath, constants.UncloudAPIPort, mapper)
+	clusterAPIServer := grpc.NewServer(
 		grpc.ForceServerCodecV2(proxy.Codec()),
 		grpc.UnaryInterceptor(grpcversion.ServerUnaryInterceptor),
 		grpc.StreamInterceptor(grpcversion.ServerStreamInterceptor),
@@ -291,7 +300,7 @@ func NewMachine(config *Config) (*Machine, error) {
 		store:            corroStore,
 		cluster:          c,
 		dockerService:    dockerService,
-		localProxyServer: localProxyServer,
+		clusterAPIServer: clusterAPIServer,
 		proxyDirector:    proxyDirector,
 	}
 
@@ -316,7 +325,7 @@ func NewMachine(config *Config) (*Machine, error) {
 	caddyStorageServer := caddystorage.NewServer(caddyStore)
 
 	leaseServer := distlockgrpc.NewServer(distlock.NewMemoryStore())
-	m.localMachineServer = newGRPCServer(m, c, m.dockerServer, caddyServer, caddyStorageServer, leaseServer)
+	m.machineAPIServer = newGRPCServer(m, c, m.dockerServer, caddyServer, caddyStorageServer, leaseServer)
 
 	if m.Initialised() {
 		close(m.initialised)
@@ -343,7 +352,7 @@ func newGRPCServer(
 	return s
 }
 
-// Started returns a channel that is closed when the machine is ready to serve requests on the local API server.
+// Started returns a channel that is closed when the machine and cluster API servers are ready to serve requests.
 func (m *Machine) Started() <-chan struct{} {
 	return m.started
 }
@@ -395,21 +404,54 @@ func (m *Machine) Run(ctx context.Context) error {
 	// Create a cancellable context for the Run method to allow stopping the machine gracefully.
 	ctx, m.stop = context.WithCancel(ctx)
 
+	// Take over the systemd-activated socket for the cluster API if provided, otherwise bind to the configured
+	// Unix socket path.
+	clusterAPIListener := m.config.ClusterAPIListener
+	clusterAPISockPath := m.config.ClusterAPISockPath
+	if clusterAPIListener != nil {
+		if clusterAPIListener.Addr().Network() == "unix" {
+			clusterAPISockPath = clusterAPIListener.Addr().String()
+		} else {
+			clusterAPISockPath = ""
+		}
+		defer clusterAPIListener.Close()
+	}
+
+	sockGID, err := socketGID()
+	if err != nil {
+		return err
+	}
+	if err = prepareUnixSocketDirectory(m.config.MachineAPISockPath, sockGID); err != nil {
+		return fmt.Errorf("prepare machine API Unix socket directory: %w", err)
+	}
+	// The cluster API socket activated by systemd may have been created with root group ownership.
+	// Apply the intended access permissions.
+	if clusterAPISockPath != "" {
+		if err = prepareUnixSocketDirectory(clusterAPISockPath, sockGID); err != nil {
+			return fmt.Errorf("prepare cluster API Unix socket directory: %w", err)
+		}
+	}
+
 	// Docker dependency is essential for the machine to function. Block until it's ready.
 	if err := docker.WaitDaemonReady(ctx, m.config.DockerClient); err != nil {
 		return fmt.Errorf("wait for Docker daemon: %w", err)
 	}
 	defer m.config.DockerClient.Close()
 
-	// Bind the local API listeners before starting the dependencies (e.g. corrosion) to not deal with the teardown
+	// Bind the API listeners before starting the dependencies (e.g. corrosion) to not deal with the teardown
 	// on failure.
-	machineListener, err := listenUnixSocket(m.config.MachineSockPath)
+	machineAPIListener, err := sockets.NewUnixSocket(m.config.MachineAPISockPath, sockGID)
 	if err != nil {
-		return fmt.Errorf("listen machine API unix socket %q: %w", m.config.MachineSockPath, err)
+		return fmt.Errorf("listen machine API Unix socket %q: %w", m.config.MachineAPISockPath, err)
 	}
-	proxyListener, err := listenUnixSocket(m.config.UncloudSockPath)
-	if err != nil {
-		return fmt.Errorf("listen API proxy unix socket %q: %w", m.config.UncloudSockPath, err)
+	defer machineAPIListener.Close()
+
+	if clusterAPIListener == nil {
+		clusterAPIListener, err = sockets.NewUnixSocket(clusterAPISockPath, sockGID)
+		if err != nil {
+			return fmt.Errorf("listen cluster API Unix socket %q: %w", clusterAPISockPath, err)
+		}
+		defer clusterAPIListener.Close()
 	}
 
 	// Configure and start the corrosion service on the loopback if the machine is not initialised as a cluster
@@ -437,20 +479,20 @@ func (m *Machine) Run(ctx context.Context) error {
 	// Use an errgroup to coordinate error handling and graceful shutdown of multiple machine components.
 	errGroup, ctx := errgroup.WithContext(ctx)
 
-	// Start the local machine API server.
+	// Start the API server that handles requests directly on this machine.
 	errGroup.Go(func() error {
-		slog.Info("Starting local machine API server.", "path", m.config.MachineSockPath)
-		if err := m.localMachineServer.Serve(machineListener); err != nil {
-			return fmt.Errorf("local machine API server failed: %w", err)
+		slog.Info("Starting machine API server.", "path", m.config.MachineAPISockPath)
+		if err := m.machineAPIServer.Serve(machineAPIListener); err != nil {
+			return fmt.Errorf("machine API server failed: %w", err)
 		}
 		return nil
 	})
 
-	// Start the local API proxy server.
+	// Start the client-facing API server that routes requests across the cluster.
 	errGroup.Go(func() error {
-		slog.Info("Starting local API proxy server.", "path", m.config.UncloudSockPath)
-		if err := m.localProxyServer.Serve(proxyListener); err != nil {
-			return fmt.Errorf("local API proxy server failed: %w", err)
+		slog.Info("Starting cluster API server.", "path", clusterAPIListener.Addr().String())
+		if err := m.clusterAPIServer.Serve(clusterAPIListener); err != nil {
+			return fmt.Errorf("cluster API server failed: %w", err)
 		}
 		return nil
 	})
@@ -478,7 +520,7 @@ func (m *Machine) Run(ctx context.Context) error {
 
 			slog.Info("Starting cluster controller.")
 			// Update the proxy director's local address to the machine's management IP address, allowing
-			// the proxy to identify which requests should be proxied to the local machine API server.
+			// the proxy to identify which requests should be handled by the local API server.
 			m.proxyDirector.UpdateLocalAddress(m.state.Network.ManagementIP.String())
 			proxyServer := grpc.NewServer(
 				grpc.ForceServerCodecV2(proxy.Codec()),
@@ -577,17 +619,17 @@ func (m *Machine) Run(ctx context.Context) error {
 	// Shutdown goroutine.
 	errGroup.Go(func() error {
 		<-ctx.Done()
-		slog.Info("Stopping local machine API server.")
+		slog.Info("Stopping machine API server.")
 		// TODO: implement timeout for graceful shutdown.
-		m.localMachineServer.GracefulStop()
-		slog.Info("Local machine API server stopped.")
+		m.machineAPIServer.GracefulStop()
+		slog.Info("Machine API server stopped.")
 
-		slog.Info("Stopping local API proxy server.")
+		slog.Info("Stopping cluster API server.")
 		// TODO: implement timeout for graceful shutdown.
-		m.localProxyServer.GracefulStop()
+		m.clusterAPIServer.GracefulStop()
 		// Close the proxy director to close all backend connections.
 		m.proxyDirector.Close()
-		slog.Info("Local API proxy server stopped.")
+		slog.Info("Cluster API server stopped.")
 
 		return nil
 	})
@@ -616,38 +658,46 @@ func (m *Machine) Run(ctx context.Context) error {
 	return err
 }
 
-// listenUnixSocket creates a new Unix socket listener with the specified path. The socket file is created with 0660
-// access mode and uncloud group if the group is found, otherwise it falls back to the root group.
-func listenUnixSocket(path string) (net.Listener, error) {
+// socketGID returns the uncloud group ID, or the root group ID if the uncloud group does not exist.
+func socketGID() (int, error) {
 	gid := 0 // Fall back to the root group if the uncloud group is not found.
 	group, err := user.LookupGroup(DefaultSockGroup)
 	if err != nil {
 		//goland:noinspection GoTypeAssertionOnErrors
 		if _, ok := err.(user.UnknownGroupError); ok {
 			slog.Info(
-				"Specified group not found, using root group for the API socket.",
-				"group", DefaultSockGroup, "path", path,
+				"Specified group not found, using root group for API sockets.",
+				"group", DefaultSockGroup,
 			)
 		} else {
-			return nil, fmt.Errorf("lookup %q group ID (GID): %w", DefaultSockGroup, err)
+			return 0, fmt.Errorf("lookup %q group ID (GID): %w", DefaultSockGroup, err)
 		}
 	} else {
 		gid, err = strconv.Atoi(group.Gid)
 		if err != nil {
-			return nil, fmt.Errorf("parse %q group ID (GID) %q: %w", DefaultSockGroup, group.Gid, err)
+			return 0, fmt.Errorf("parse %q group ID (GID) %q: %w", DefaultSockGroup, group.Gid, err)
 		}
 	}
 
-	// Ensure the parent directory exists and has the correct group permissions.
+	return gid, nil
+}
+
+// prepareUnixSocketDirectory ensures the socket's parent directory has the intended group and permissions.
+func prepareUnixSocketDirectory(path string, gid int) error {
 	parent, _ := filepath.Split(path)
-	if err = os.MkdirAll(parent, 0o750); err != nil {
-		return nil, fmt.Errorf("create directory %q: %w", parent, err)
+	if err := os.MkdirAll(parent, 0o750); err != nil {
+		return fmt.Errorf("create directory %q: %w", parent, err)
 	}
-	if err = os.Chown(parent, -1, gid); err != nil {
-		return nil, fmt.Errorf("chown directory %q: %w", parent, err)
+	if err := os.Chown(parent, -1, gid); err != nil {
+		return fmt.Errorf("chown directory %q: %w", parent, err)
+	}
+	// MkdirAll preserves the mode of an existing directory. A Docker container may have created the bind-mount source
+	// first, so apply the intended mode explicitly.
+	if err := os.Chmod(parent, 0o750); err != nil {
+		return fmt.Errorf("chmod directory %q: %w", parent, err)
 	}
 
-	return sockets.NewUnixSocket(path, gid)
+	return nil
 }
 
 func (m *Machine) configureCorrosion() error {

pkg/client/connector/ssh.go

@@ -35,7 +35,7 @@ func (cfg *SSHConnectorConfig) Destination() string {
 	return dst
 }
 
-// SSHConnector establishes a connection to the machine API through an SSH tunnel to the machine.
+// SSHConnector establishes a connection to the Uncloud API through an SSH tunnel to the machine.
 type SSHConnector struct {
 	config SSHConnectorConfig
 	client *ssh.Client
@@ -69,7 +69,7 @@ func (c *SSHConnector) Connect(ctx context.Context) (*grpc.ClientConn, error) {
 
 	sockPath := c.config.SockPath
 	if sockPath == "" {
-		sockPath = machine.DefaultUncloudSockPath
+		sockPath = machine.DefaultClusterAPISockPath
 	}
 	conn, err := grpc.NewClient(
 		"unix://"+sockPath,
@@ -83,7 +83,7 @@ func (c *SSHConnector) Connect(ctx context.Context) (*grpc.ClientConn, error) {
 				conn, dErr := c.client.DialContext(ctx, "unix", addr)
 				if dErr != nil {
 					return nil, fmt.Errorf(
-						"connect to machine API socket '%s' through SSH tunnel (is uncloud.service running "+
+						"connect to Uncloud API socket '%s' through SSH tunnel (is uncloud.service running "+
 							"on the remote machine and does the SSH user '%s' have permissions to access the socket?):"+
 							" %w",
 						addr, c.client.User(), dErr,
@@ -94,7 +94,7 @@ func (c *SSHConnector) Connect(ctx context.Context) (*grpc.ClientConn, error) {
 		),
 	)
 	if err != nil {
-		return nil, fmt.Errorf("create machine API client: %w", err)
+		return nil, fmt.Errorf("create Uncloud API client: %w", err)
 	}
 	return conn, nil
 }

pkg/client/connector/sshcli.go

@@ -19,7 +19,7 @@ import (
 	"google.golang.org/grpc/credentials/insecure"
 )
 
-// SSHCLIConnector establishes a connection to the machine API by executing SSH CLI
+// SSHCLIConnector establishes a connection to the Uncloud API by executing SSH CLI
 // and running `uncloudd dial-stdio` on the remote machine.
 type SSHCLIConnector struct {
 	config SSHConnectorConfig
@@ -104,7 +104,7 @@ func (c *SSHCLIConnector) Connect(ctx context.Context) (*grpc.ClientConn, error)
 		}),
 	)
 	if err != nil {
-		return nil, fmt.Errorf("create machine API client: %w", err)
+		return nil, fmt.Errorf("create Uncloud API client: %w", err)
 	}
 
 	return grpcConn, nil

pkg/client/connector/tcp.go

@@ -13,7 +13,7 @@ import (
 	"google.golang.org/grpc/credentials/insecure"
 )
 
-// TCPConnector establishes a connection to the machine API through a direct TCP connection to an API endpoint.
+// TCPConnector establishes a connection to the Uncloud API through a direct TCP connection.
 type TCPConnector struct {
 	apiAddr netip.AddrPort
 }
@@ -40,7 +40,7 @@ func (c *TCPConnector) Connect(_ context.Context) (*grpc.ClientConn, error) {
 		grpc.WithStreamInterceptor(grpcversion.ClientStreamInterceptor),
 	)
 	if err != nil {
-		return nil, fmt.Errorf("create machine API client: %w", err)
+		return nil, fmt.Errorf("create Uncloud API client: %w", err)
 	}
 	return conn, nil
 }

pkg/client/connector/unix.go

@@ -10,7 +10,7 @@ import (
 	"google.golang.org/grpc/credentials/insecure"
 )
 
-// UnixConnector establishes a connection to the machine API through a unix domain socket.
+// UnixConnector establishes a connection to the Uncloud API through a Unix domain socket.
 type UnixConnector struct {
 	socketPath string
 }
@@ -31,7 +31,7 @@ func (c *UnixConnector) Connect(_ context.Context) (*grpc.ClientConn, error) {
 		grpc.WithStreamInterceptor(grpcversion.ClientStreamInterceptor),
 	)
 	if err != nil {
-		return nil, fmt.Errorf("create machine API client: %w", err)
+		return nil, fmt.Errorf("create Uncloud API client: %w", err)
 	}
 	return conn, nil
 }

scripts/docker/entrypoint.sh

@@ -35,9 +35,9 @@ echo "Docker in Docker is ready."
 echo "Loading corrosion image from /images/corrosion.tar..."
 docker load < /images/corrosion.tar
 
-# Make machine API accessible from the host via port publishing.
-echo "Proxying Uncloud API port 51000/tcp to Unix socket /run/uncloud/uncloud.sock..."
-socat TCP-LISTEN:51000,reuseaddr,fork,bind="$(hostname -i)" UNIX-CONNECT:/run/uncloud/uncloud.sock &
+# Make the Uncloud API accessible from the host via port publishing.
+echo "Proxying Uncloud API port 51000/tcp to Unix socket /run/uncloud/api/uncloud.sock..."
+socat TCP-LISTEN:51000,reuseaddr,fork,bind="$(hostname -i)" UNIX-CONNECT:/run/uncloud/api/uncloud.sock &
 
 # Execute the passed command and wait for it while maintaining signal handling.
 "$@" &

scripts/install.sh

@@ -277,11 +277,33 @@ install_uncloud_binaries() {
 }
 
 install_uncloud_systemd() {
+    local uncloud_socket_path="${INSTALL_SYSTEMD_DIR}/uncloud.socket"
     local uncloud_service_path="${INSTALL_SYSTEMD_DIR}/uncloud.service"
+
+    mkdir -p "${INSTALL_SYSTEMD_DIR}"
+
+    cat > "${uncloud_socket_path}" << EOF
+[Unit]
+Description=Uncloud API socket
+Before=docker.service
+
+[Socket]
+ListenStream=/run/uncloud/api/uncloud.sock
+SocketUser=root
+SocketGroup=uncloud
+SocketMode=0660
+DirectoryMode=0750
+
+[Install]
+WantedBy=sockets.target
+EOF
+    log "✓ Systemd unit file created: ${uncloud_socket_path}"
+
     cat > "${uncloud_service_path}" << EOF
 [Unit]
 Description=Uncloud machine daemon
-After=network-online.target docker.service
+Requires=uncloud.socket
+After=network-online.target uncloud.socket docker.service
 Wants=network-online.target
 
 [Service]
@@ -306,12 +328,11 @@ WantedBy=multi-user.target
 EOF
     log "✓ Systemd unit file created: ${uncloud_service_path}"
 
-
     if [[ "${INSTALL_ONLY}" != "true" ]]; then
         # Reload systemd to recognize the new or updated unit file.
         systemctl daemon-reload
     fi
-    systemctl enable uncloud.service
+    systemctl enable uncloud.socket uncloud.service
 }
 
 start_uncloud() {

scripts/uninstall.sh

@@ -57,14 +57,17 @@ fi
 
 log "⏳ Stopping systemd services..."
 systemctl stop uncloud.service || log "uncloud.service not running or doesn't exist."
+systemctl stop uncloud.socket || log "uncloud.socket not running or doesn't exist."
 # TODO: remove uncloud-corrosion.service handling in 0.22 once pre-0.20 systemd installs are gone.
 systemctl stop uncloud-corrosion.service || log "uncloud-corrosion.service not running or doesn't exist."
 systemctl disable uncloud.service || log "uncloud.service already disabled or doesn't exist."
+systemctl disable uncloud.socket || log "uncloud.socket already disabled or doesn't exist."
 systemctl disable uncloud-corrosion.service || log "uncloud-corrosion.service already disabled or doesn't exist."
 log "✓ Systemd services stopped."
 
 log "⏳ Removing systemd service files..."
 rm -fv "${INSTALL_SYSTEMD_DIR}/uncloud.service"
+rm -fv "${INSTALL_SYSTEMD_DIR}/uncloud.socket"
 # TODO: remove uncloud-corrosion.service handling in 0.22 once pre-0.20 systemd installs are gone.
 rm -fv "${INSTALL_SYSTEMD_DIR}/uncloud-corrosion.service"
 systemctl daemon-reload

website/docs/2-getting-started/2-deploy-demo-app.md

@@ -142,7 +142,9 @@ WARNING: Access to the remote API on a privileged Docker daemon is equivalent
 ✓ uncloudd binary installed: /usr/local/bin/uncloudd
 ⏳ Downloading uninstall script: https://raw.githubusercontent.com/psviderski/uncloud/refs/heads/main/scripts/uninstall.sh
 ✓ uncloud-uninstall script installed: /usr/local/bin/uncloud-uninstall
+✓ Systemd unit file created: /etc/systemd/system/uncloud.socket
 ✓ Systemd unit file created: /etc/systemd/system/uncloud.service
+Created symlink /etc/systemd/system/sockets.target.wants/uncloud.socket → /etc/systemd/system/uncloud.socket.
 Created symlink /etc/systemd/system/multi-user.target.wants/uncloud.service → /etc/systemd/system/uncloud.service.
 ⏳ Starting Uncloud machine daemon (uncloud.service)...
 ✓ Uncloud machine daemon started.
@@ -393,9 +395,11 @@ The following actions will be performed:
 Do you want to proceed with uninstallation? [y/N] y
 ⏳ Stopping systemd services...
 Removed /etc/systemd/system/multi-user.target.wants/uncloud.service.
+Removed /etc/systemd/system/sockets.target.wants/uncloud.socket.
 ✓ Systemd services stopped.
 ⏳ Removing systemd service files...
 removed '/etc/systemd/system/uncloud.service'
+removed '/etc/systemd/system/uncloud.socket'
 ✓ Systemd service files removed.
 ⏳ Removing binaries...
 removed '/usr/local/bin/uncloudd'

website/docs/3-concepts/1-clusters/1-connecting.md

@@ -17,9 +17,9 @@ cluster. It has a name and a list of connection details for the machines in that
 A context is not the same thing as a cluster. It is your local view of a cluster: which machines you can connect through
 and in what order to try them. Different people or environments may need to reach the same cluster in different ways.
 
-You can also manually create multiple contexts for the same cluster. For example, one that connects through
-a machine with a public IP when you're not in the office, and another that connects through a private machine on the
-office network when you're on-site to reduce latency. You can switch between them depending on where you are.
+You can also manually create multiple contexts for the same cluster. For example, one that connects through a machine
+with a public IP when you're not in the office, and another that connects through a private machine on the office
+network when you're on-site to reduce latency. You can switch between them depending on where you are.
 
 ### Managing contexts
 
@@ -46,11 +46,14 @@ When you run a `uc` command, it determines which cluster to connect to using thi
 Once the context is resolved, `uc` tries each connection in the context's `connections` list in order until one
 succeeds.
 
-## User permissions on the machine
+## API socket access
 
-When `uc` connects to a machine over SSH, it communicates with the Uncloud daemon through the Unix socket
-`/run/uncloud/uncloud.sock` on that machine. The daemon restricts access to the socket to the `root` user and members
-of the `uncloud` Linux group. This means your SSH user must be either `root` or a member of the `uncloud` group.
+The Uncloud daemon exposes the API through the Unix socket `/run/uncloud/api/uncloud.sock` on each machine. It restricts
+access to the `root` user and members of the `uncloud` Linux group.
+
+### User access
+
+When `uc` connects to a machine over SSH, the SSH user must be either `root` or a member of the `uncloud` group.
 
 In most cases you don't need to set this up manually. When you initialise or add a machine with a non-root user,
 `uc machine init` and `uc machine add` automatically add that user to the `uncloud` group during installation.
@@ -67,6 +70,21 @@ user, close any long-running SSH connections to the machine (for example, SSH Co
 The same requirement applies when running `uc` locally on a cluster machine with a `unix://` connection. The local user
 must be `root` or a member of the `uncloud` group.
 
+### Container access
+
+If a container needs to talk to the Uncloud API over the socket, mount `/run/uncloud/api` as a read-only directory. Do
+not mount the socket file directly. The directory mount lets the container see a replacement socket after the daemon
+restarts.
+
+:::warning Full cluster access
+
+Mounting the Uncloud API socket gives the container the same cluster-wide privileges as a local `uc` client. A process
+with access can manage workloads across the cluster and may be able to gain root access to cluster machines through the
+workloads it creates. Treat the Uncloud API socket like the Docker socket. Only mount it into containers that you fully
+trust.
+
+:::
+
 ## Global flags and environment variables
 
 These flags are available on every `uc` command. They can also be set with an environment variable. The flag takes
@@ -95,11 +113,11 @@ uc --connect ssh://root@203.0.113.1 ls
 # Go's built-in SSH library (no SSH config support, useful when the system ssh is not available)
 uc --connect ssh+go://root@203.0.113.1 ls
 
-# Direct connection to machine gRPC API over TCP (for advanced users with custom setups)
+# Direct connection to the Uncloud API over TCP (for advanced users with custom setups)
 uc --connect tcp://[fdcc:4439:f545:3ca:5d17:66e5:7c96:40bd]:51000 ls
 
-# Direct connection to machine gRPC API over a Unix socket (for running uc locally on a cluster machine)
-uc --connect unix:///run/uncloud/uncloud.sock ls
+# Direct connection to the Uncloud API over a Unix socket (for running uc locally on a cluster machine)
+uc --connect unix:///run/uncloud/api/uncloud.sock ls
 ```
 
 :::info

website/docs/7-cli-config-reference.md

@@ -68,12 +68,12 @@ next one. You can change the default connection with an interactive command
 
 Every connection must have exactly one connection type attribute:
 
-| Attribute | Format                      | Description                                                                                                                        |
-|-----------|-----------------------------|------------------------------------------------------------------------------------------------------------------------------------|
-| `ssh`     | `user@host[:port]`          | Connect using the system `ssh` command with full SSH config support (default for new connections added with `uc machine init/add`) |
-| `ssh_go`  | `user@host[:port]`          | Connect using Go's built-in SSH library (no SSH config support)                                                                |
-| `tcp`     | `host:port`                 | Connect directly to the machine gRPC API over TCP (for advanced users with custom setups)                                          |
-| `unix`    | `/run/uncloud/uncloud.sock` | Connect directly to the machine gRPC API over a Unix socket (for running `uc` locally on the cluster machines)                     |
+| Attribute | Format                          | Description                                                                                                                        |
+|-----------|---------------------------------|------------------------------------------------------------------------------------------------------------------------------------|
+| `ssh`     | `user@host[:port]`              | Connect using the system `ssh` command with full SSH config support (default for new connections added with `uc machine init/add`) |
+| `ssh_go`  | `user@host[:port]`              | Connect using Go's built-in SSH library (no SSH config support)                                                                    |
+| `tcp`     | `host:port`                     | Connect directly to the Uncloud API over TCP (for advanced users with custom setups)                                               |
+| `unix`    | `/run/uncloud/api/uncloud.sock` | Connect directly to the Uncloud API over a Unix socket (for running `uc` locally on a cluster machine)                             |
 
 A connection can also have these optional attributes: