Add --live-restore flag

This flags enables full support of daemonless containers in docker.  It
ensures that docker does not stop containers on shutdown or restore and
properly reconnects to the container when restarted.

This is not the default because of backwards compat but should be the
desired outcome for people running containers in prod.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

cmd/dockerd/daemon_unix.go

@@ -71,6 +71,9 @@ func (cli *DaemonCli) getPlatformRemoteOptions() []libcontainerd.RemoteOption {
 		args := []string{"--systemd-cgroup=true"}
 		opts = append(opts, libcontainerd.WithRuntimeArgs(args))
 	}
+	if cli.Config.LiveRestore {
+		opts = append(opts, libcontainerd.WithLiveRestore(true))
+	}
 	return opts
 }
 

daemon/config.go

@@ -90,6 +90,7 @@ type CommonConfig struct {
 	TrustKeyPath         string              `json:"-"`
 	CorsHeaders          string              `json:"api-cors-header,omitempty"`
 	EnableCors           bool                `json:"api-enable-cors,omitempty"`
+	LiveRestore          bool                `json:"live-restore,omitempty"`
 
 	// ClusterStore is the storage backend used for the cluster information. It is used by both
 	// multihost networking (to store networks and endpoints information) and by the node discovery

daemon/config_unix.go

@@ -82,6 +82,7 @@ func (config *Config) InstallFlags(cmd *flag.FlagSet, usageFn func(string) strin
 	cmd.StringVar(&config.CgroupParent, []string{"-cgroup-parent"}, "", usageFn("Set parent cgroup for all containers"))
 	cmd.StringVar(&config.RemappedRoot, []string{"-userns-remap"}, "", usageFn("User/Group setting for user namespaces"))
 	cmd.StringVar(&config.ContainerdAddr, []string{"-containerd"}, "", usageFn("Path to containerd socket"))
+	cmd.BoolVar(&config.LiveRestore, []string{"-live-restore"}, false, usageFn("Enable live restore of docker when containers are still running"))
 
 	config.attachExperimentalFlags(cmd, usageFn)
 }

daemon/daemon.go

@@ -92,6 +92,7 @@ type Daemon struct {
 	nameIndex                 *registrar.Registrar
 	linkIndex                 *linkIndex
 	containerd                libcontainerd.Client
+	containerdRemote          libcontainerd.Remote
 	defaultIsolation          containertypes.Isolation // Default isolation mode on Windows
 }
 
@@ -542,6 +543,7 @@ func NewDaemon(config *Config, registryService registry.Service, containerdRemot
 
 	d.nameIndex = registrar.NewRegistrar()
 	d.linkIndex = newLinkIndex()
+	d.containerdRemote = containerdRemote
 
 	go d.execCommandGC()
 
@@ -599,6 +601,11 @@ func (daemon *Daemon) shutdownContainer(c *container.Container) error {
 // Shutdown stops the daemon.
 func (daemon *Daemon) Shutdown() error {
 	daemon.shutdown = true
+	// Keep mounts and networking running on daemon shutdown if
+	// we are to keep containers running and restore them.
+	if daemon.configStore.LiveRestore {
+		return nil
+	}
 	if daemon.containers != nil {
 		logrus.Debug("starting clean shutdown of all containers...")
 		daemon.containers.ApplyAll(func(c *container.Container) {
@@ -782,6 +789,7 @@ func (daemon *Daemon) initDiscovery(config *Config) error {
 // - Daemon max concurrent downloads
 // - Daemon max concurrent uploads
 // - Cluster discovery (reconfigure and restart).
+// - Daemon live restore
 func (daemon *Daemon) Reload(config *Config) error {
 	daemon.configStore.reloadLock.Lock()
 	defer daemon.configStore.reloadLock.Unlock()
@@ -796,6 +804,13 @@ func (daemon *Daemon) Reload(config *Config) error {
 	if config.IsValueSet("debug") {
 		daemon.configStore.Debug = config.Debug
 	}
+	if config.IsValueSet("live-restore") {
+		daemon.configStore.LiveRestore = config.LiveRestore
+		if err := daemon.containerdRemote.UpdateOptions(libcontainerd.WithLiveRestore(config.LiveRestore)); err != nil {
+			return err
+		}
+
+	}
 
 	// If no value is set for max-concurrent-downloads we assume it is the default value
 	// We always "reset" as the cost is lightweight and easy to maintain.

docs/admin/configuring.md

@@ -278,3 +278,16 @@ be viewed using `journalctl -u docker`
     May 06 00:22:06 localhost.localdomain docker[2495]: time="2015-05-06T00:22:06Z" level="info" msg="-job acceptconnections() = OK (0)"
 
 _Note: Using and configuring journal is an advanced topic and is beyond the scope of this article._
+
+
+### Daemonless Containers
+
+Starting with Docker 1.12 containers can run without Docker or containerd running.  This allows the 
+Docker daemon to exit, be upgraded, or recover from a crash without affecting running containers 
+on the system.  To enable this functionality you need to add the `--live-restore` flag when
+launching `dockerd`.  This will ensure that Docker does not kill containers on graceful shutdown or
+on restart leaving the containers running.
+
+While the Docker daemon is down logging will still be captured, however, it will be capped at the kernel's pipe buffer size before the buffer fills up, blocking the process.
+Docker will need to be restarted to flush these buffers.
+You can modify the kernel's buffer size by changing `/proc/sys/fs/pipe-max-size`.

integration-cli/docker_cli_daemon_experimental_test.go

@@ -63,7 +63,7 @@ func (s *DockerDaemonSuite) TestDaemonRestartWithKilledRunningContainer(t *check
 // them now, should remove the mounts.
 func (s *DockerDaemonSuite) TestCleanupMountsAfterDaemonCrash(c *check.C) {
 	testRequires(c, DaemonIsLinux)
-	c.Assert(s.d.StartWithBusybox(), check.IsNil)
+	c.Assert(s.d.StartWithBusybox("--live-restore"), check.IsNil)
 
 	out, err := s.d.Cmd("run", "-d", "busybox", "top")
 	c.Assert(err, check.IsNil, check.Commentf("Output: %s", out))
@@ -78,7 +78,7 @@ func (s *DockerDaemonSuite) TestCleanupMountsAfterDaemonCrash(c *check.C) {
 	c.Assert(strings.Contains(string(mountOut), id), check.Equals, true, comment)
 
 	// restart daemon.
-	if err := s.d.Restart(); err != nil {
+	if err := s.d.Restart("--live-restore"); err != nil {
 		c.Fatal(err)
 	}
 
@@ -103,7 +103,7 @@ func (s *DockerDaemonSuite) TestCleanupMountsAfterDaemonCrash(c *check.C) {
 
 // TestDaemonRestartWithPausedRunningContainer requires live restore of running containers
 func (s *DockerDaemonSuite) TestDaemonRestartWithPausedRunningContainer(t *check.C) {
-	if err := s.d.StartWithBusybox(); err != nil {
+	if err := s.d.StartWithBusybox("--live-restore"); err != nil {
 		t.Fatal(err)
 	}
 
@@ -130,7 +130,7 @@ func (s *DockerDaemonSuite) TestDaemonRestartWithPausedRunningContainer(t *check
 	time.Sleep(3 * time.Second)
 
 	// restart the daemon
-	if err := s.d.Start(); err != nil {
+	if err := s.d.Start("--live-restore"); err != nil {
 		t.Fatal(err)
 	}
 
@@ -148,7 +148,7 @@ func (s *DockerDaemonSuite) TestDaemonRestartWithPausedRunningContainer(t *check
 func (s *DockerDaemonSuite) TestDaemonRestartWithUnpausedRunningContainer(t *check.C) {
 	// TODO(mlaventure): Not sure what would the exit code be on windows
 	testRequires(t, DaemonIsLinux)
-	if err := s.d.StartWithBusybox(); err != nil {
+	if err := s.d.StartWithBusybox("--live-restore"); err != nil {
 		t.Fatal(err)
 	}
 
@@ -180,7 +180,7 @@ func (s *DockerDaemonSuite) TestDaemonRestartWithUnpausedRunningContainer(t *che
 	time.Sleep(3 * time.Second)
 
 	// restart the daemon
-	if err := s.d.Start(); err != nil {
+	if err := s.d.Start("--live-restore"); err != nil {
 		t.Fatal(err)
 	}
 

libcontainerd/client_linux.go

@@ -8,6 +8,7 @@ import (
 	"strings"
 	"sync"
 	"syscall"
+	"time"
 
 	"github.com/Sirupsen/logrus"
 	containerd "github.com/docker/containerd/api/grpc/types"
@@ -24,6 +25,7 @@ type client struct {
 	remote        *remote
 	q             queue
 	exitNotifiers map[string]*exitNotifier
+	liveRestore   bool
 }
 
 func (clnt *client) AddProcess(containerID, processFriendlyName string, specp Process) error {
@@ -445,13 +447,48 @@ func (clnt *client) restore(cont *containerd.Container, options ...CreateOption)
 }
 
 func (clnt *client) Restore(containerID string, options ...CreateOption) error {
+	if clnt.liveRestore {
+		cont, err := clnt.getContainerdContainer(containerID)
+		if err == nil && cont.Status != "stopped" {
+			if err := clnt.restore(cont, options...); err != nil {
+				logrus.Errorf("error restoring %s: %v", containerID, err)
+			}
+			return nil
+		}
+		return clnt.setExited(containerID)
+	}
+
 	cont, err := clnt.getContainerdContainer(containerID)
 	if err == nil && cont.Status != "stopped" {
-		if err := clnt.restore(cont, options...); err != nil {
-			logrus.Errorf("error restoring %s: %v", containerID, err)
+		w := clnt.getOrCreateExitNotifier(containerID)
+		clnt.lock(cont.Id)
+		container := clnt.newContainer(cont.BundlePath)
+		container.systemPid = systemPid(cont)
+		clnt.appendContainer(container)
+		clnt.unlock(cont.Id)
+
+		container.discardFifos()
+
+		if err := clnt.Signal(containerID, int(syscall.SIGTERM)); err != nil {
+			logrus.Errorf("error sending sigterm to %v: %v", containerID, err)
+		}
+		select {
+		case <-time.After(10 * time.Second):
+			if err := clnt.Signal(containerID, int(syscall.SIGKILL)); err != nil {
+				logrus.Errorf("error sending sigkill to %v: %v", containerID, err)
+			}
+			select {
+			case <-time.After(2 * time.Second):
+			case <-w.wait():
+				return nil
+			}
+		case <-w.wait():
+			return nil
 		}
-		return nil
 	}
+
+	clnt.deleteContainer(containerID)
+
 	return clnt.setExited(containerID)
 }
 

libcontainerd/container_linux.go

@@ -2,6 +2,7 @@ package libcontainerd
 
 import (
 	"encoding/json"
+	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -194,3 +195,18 @@ func (ctr *container) handleEvent(e *containerd.Event) error {
 	}
 	return nil
 }
+
+// discardFifos attempts to fully read the container fifos to unblock processes
+// that may be blocked on the writer side.
+func (ctr *container) discardFifos() {
+	for _, i := range []int{syscall.Stdout, syscall.Stderr} {
+		f := ctr.fifo(i)
+		c := make(chan struct{})
+		go func() {
+			close(c) // this channel is used to not close the writer too early, before readonly open has been called.
+			io.Copy(ioutil.Discard, openReaderFromFifo(f))
+		}()
+		<-c
+		closeReaderFifo(f) // avoid blocking permanently on open if there is no writer side
+	}
+}

libcontainerd/remote.go

@@ -9,6 +9,8 @@ type Remote interface {
 	// Cleanup stops containerd if it was started by libcontainerd.
 	// Note this is not used on Windows as there is no remote containerd.
 	Cleanup()
+	// UpdateOptions allows various remote options to be updated at runtime.
+	UpdateOptions(...RemoteOption) error
 }
 
 // RemoteOption allows to configure parameters of remotes.

libcontainerd/remote_linux.go

@@ -52,6 +52,7 @@ type remote struct {
 	pastEvents    map[string]*containerd.Event
 	runtimeArgs   []string
 	daemonWaitCh  chan struct{}
+	liveRestore   bool
 }
 
 // New creates a fresh instance of libcontainerd remote.
@@ -111,6 +112,15 @@ func New(stateDir string, options ...RemoteOption) (_ Remote, err error) {
 	return r, nil
 }
 
+func (r *remote) UpdateOptions(options ...RemoteOption) error {
+	for _, option := range options {
+		if err := option.Apply(r); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 func (r *remote) handleConnectionChange() {
 	var transientFailureCount = 0
 	state := grpc.Idle
@@ -184,6 +194,7 @@ func (r *remote) Client(b Backend) (Client, error) {
 		},
 		remote:        r,
 		exitNotifiers: make(map[string]*exitNotifier),
+		liveRestore:   r.liveRestore,
 	}
 
 	r.Lock()
@@ -460,3 +471,21 @@ func (d debugLog) Apply(r Remote) error {
 	}
 	return fmt.Errorf("WithDebugLog option not supported for this remote")
 }
+
+// WithLiveRestore defines if containers are stopped on shutdown or restored.
+func WithLiveRestore(v bool) RemoteOption {
+	return liveRestore(v)
+}
+
+type liveRestore bool
+
+func (l liveRestore) Apply(r Remote) error {
+	if remote, ok := r.(*remote); ok {
+		remote.liveRestore = bool(l)
+		for _, c := range remote.clients {
+			c.liveRestore = bool(l)
+		}
+		return nil
+	}
+	return fmt.Errorf("WithLiveRestore option not supported for this remote")
+}

libcontainerd/remote_solaris.go

@@ -19,7 +19,16 @@ func (r *remote) Client(b Backend) (Client, error) {
 func (r *remote) Cleanup() {
 }
 
+func (r *remote) UpdateOptions(opts ...RemoteOption) error {
+	return nil
+}
+
 // New creates a fresh instance of libcontainerd remote.
 func New(_ string, _ ...RemoteOption) (Remote, error) {
 	return &remote{}, nil
 }
+
+// WithLiveRestore is a noop on solaris.
+func WithLiveRestore(v bool) RemoteOption {
+	return nil
+}

libcontainerd/remote_windows.go

@@ -20,8 +20,17 @@ func (r *remote) Client(b Backend) (Client, error) {
 func (r *remote) Cleanup() {
 }
 
+func (r *remote) UpdateOptions(opts ...RemoteOption) error {
+	return nil
+}
+
 // New creates a fresh instance of libcontainerd remote. On Windows,
 // this is not used as there is no remote containerd process.
 func New(_ string, _ ...RemoteOption) (Remote, error) {
 	return &remote{}, nil
 }
+
+// WithLiveRestore is a noop on windows.
+func WithLiveRestore(v bool) RemoteOption {
+	return nil
+}

man/dockerd.8.md

@@ -42,6 +42,7 @@ dockerd - Enable daemon mode
 [**--isolation**[=*default*]]
 [**-l**|**--log-level**[=*info*]]
 [**--label**[=*[]*]]
+[**--live-restore**[=*false*]]
 [**--log-driver**[=*json-file*]]
 [**--log-opt**[=*map[]*]]
 [**--mtu**[=*0*]]
@@ -195,6 +196,9 @@ is `hyperv`. Linux only supports `default`.
 **--label**="[]"
   Set key=value labels to the daemon (displayed in `docker info`)
 
+**--live-restore**=*false*
+  Enable live restore of running containers when the daemon starts so that they are not restarted.
+
 **--log-driver**="*json-file*|*syslog*|*journald*|*gelf*|*fluentd*|*awslogs*|*splunk*|*etwlogs*|*gcplogs*|*none*"
   Default driver for container logs. Default is `json-file`.
   **Warning**: `docker logs` command works only for `json-file` logging driver.