@@ -297,6 +297,9 @@ func (container *Container) Start() (err error) {

 	if err := container.initializeNetworking(); err != nil {

 		return err

 	}

+	if err := container.updateParentsHosts(); err != nil {

+		return err

+	}

 	container.verifyDaemonSettings()

 	if err := prepareVolumesForContainer(container); err != nil {

 		return err

@@ -390,10 +393,7 @@ func (container *Container) buildHostnameFile() error {

 	return ioutil.WriteFile(container.HostnamePath, []byte(container.Config.Hostname+"\n"), 0644)

 }

-func (container *Container) buildHostnameAndHostsFiles(IP string) error {

-	if err := container.buildHostnameFile(); err != nil {

-		return err

-	}

+func (container *Container) buildHostsFiles(IP string) error {

 	hostsPath, err := container.getRootResourcePath("hosts")

 	if err != nil {

@@ -416,6 +416,14 @@ func (container *Container) buildHostnameAndHostsFiles(IP string) error {

 	return etchosts.Build(container.HostsPath, IP, container.Config.Hostname, container.Config.Domainname, &extraContent)

 }

+func (container *Container) buildHostnameAndHostsFiles(IP string) error {

+	if err := container.buildHostnameFile(); err != nil {

+		return err

+	}

+

+	return container.buildHostsFiles(IP)

+}

+

 func (container *Container) allocateNetwork() error {

 	mode := container.hostConfig.NetworkMode

 	if container.Config.NetworkDisabled || mode.IsContainer() || mode.IsHost() {

@@ -878,6 +886,26 @@ func (container *Container) setupContainerDns() error {

 	return ioutil.WriteFile(container.ResolvConfPath, resolvConf, 0644)

 }

+func (container *Container) updateParentsHosts() error {

+	parents, err := container.daemon.Parents(container.Name)

+	if err != nil {

+		return err

+	}

+	for _, cid := range parents {

+		if cid == "0" {

+			continue

+		}

+

+		c := container.daemon.Get(cid)

+		if c != nil && !container.daemon.config.DisableNetwork && !container.hostConfig.NetworkMode.IsContainer() && !container.hostConfig.NetworkMode.IsHost() {

+			if err := etchosts.Update(c.HostsPath, container.NetworkSettings.IPAddress, container.Name[1:]); err != nil {

+				return fmt.Errorf("Failed to update /etc/hosts in parent container: %v", err)

+			}

+		}

+	}

+	return nil

+}

+

 func (container *Container) initializeNetworking() error {

 	var err error

 	if container.hostConfig.NetworkMode.IsHost() {

@@ -621,6 +621,15 @@ func (daemon *Daemon) Children(name string) (map[string]*Container, error) {

 	return children, nil

 }

+func (daemon *Daemon) Parents(name string) ([]string, error) {

+	name, err := GetFullContainerName(name)

+	if err != nil {

+		return nil, err

+	}

+

+	return daemon.containerGraph.Parents(name)

+}

+

 func (daemon *Daemon) RegisterLink(parent, child *Container, alias string) error {

 	fullName := path.Join(parent.Name, alias)

 	if !daemon.containerGraph.Exists(fullName) {

@@ -150,7 +150,10 @@ Four different options affect container domain name services.

     `CONTAINER_NAME`.  This lets processes inside the new container

     connect to the hostname `ALIAS` without having to know its IP.  The

     `--link=` option is discussed in more detail below, in the section

-    [Communication between containers](#between-containers).

+    [Communication between containers](#between-containers). Because

+    Docker may assign a different IP address to the linked containers

+    on restart, Docker updates the ALIAS entry in the /etc/hosts file

+    of the recipient containers.

  *  `--dns=IP_ADDRESS...` — sets the IP addresses added as `server`

     lines to the container's `/etc/resolv.conf` file.  Processes in the

@@ -432,6 +432,9 @@ mechanism to communicate with a linked container by its alias:

     $ docker run -d --name servicename busybox sleep 30

     $ docker run -i -t --link servicename:servicealias busybox ping -c 1 servicealias

+If you restart the source container (`servicename` in this case), the recipient

+container's `/etc/hosts` entry will be automatically updated.

+

 ## VOLUME (Shared Filesystems)

     -v=[]: Create a bind mount with: [host-dir]:[container-dir]:[rw|ro].

@@ -241,6 +241,16 @@ to make use of your `db` container.

 > example, you could have multiple (differently named) web containers attached to your

 >`db` container.

+If you restart the source container, the linked containers `/etc/hosts` files

+will be automatically updated with the source container's new IP address,

+allowing linked communication to continue.

+

+    $ sudo docker restart db

+    root@aed84ee21bde:/opt/webapp# cat /etc/hosts

+    172.17.0.7  aed84ee21bde

+    . . .

+    172.17.0.9  db

+

 # Next step

 Now that you know how to link Docker containers together, the next step is

@@ -1723,3 +1723,50 @@ func TestBindMounts(t *testing.T) {

 		t.Fatalf("Output should be %q, actual out: %q", expected, content)

 	}

 }

+

+func TestHostsLinkedContainerUpdate(t *testing.T) {

+	tmpdir, err := ioutil.TempDir("", "docker-integration")

+	if err != nil {

+		t.Fatal(err)

+	}

+	defer os.RemoveAll(tmpdir)

+

+	out, _, err := runCommandWithOutput(exec.Command(dockerBinary, "run", "-d", "--name", "c1", "busybox", "sleep", "5"))

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	// TODO fix docker cp and /etc/hosts

+	out, _, err = runCommandWithOutput(exec.Command(dockerBinary, "run", "-d", "--link", "c1:c1", "--name", "c2", "busybox", "sh", "-c", "while true;do cp /etc/hosts /hosts; done"))

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	out, _, err = runCommandWithOutput(exec.Command(dockerBinary, "cp", "c2:/hosts", tmpdir+"/1"))

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	out, _, err = runCommandWithOutput(exec.Command(dockerBinary, "restart", "-t", "0", "c1"))

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	out, _, err = runCommandWithOutput(exec.Command(dockerBinary, "cp", "c2:/hosts", tmpdir+"/2"))

+	if err != nil {

+		t.Fatal(err, out)

+	}

+

+	out, _, _, err = runCommandWithStdoutStderr(exec.Command("diff", tmpdir+"/1", tmpdir+"/2"))

+	if err == nil {

+		t.Fatalf("Expecting error, got none")

+	}

+	out = stripTrailingCharacters(out)

+	if out == "" {

+		t.Fatalf("expected /etc/hosts to be updated, but wasn't")

+	}

+

+	deleteAllContainers()

+

+	logDone("run - /etc/hosts updated in parent when restart")

+}

@@ -281,6 +281,18 @@ func (db *Database) Children(name string, depth int) ([]WalkMeta, error) {

 	return db.children(e, name, depth, nil)

 }

+// Return the parents of a specified entity

+func (db *Database) Parents(name string) ([]string, error) {

+	db.mux.RLock()

+	defer db.mux.RUnlock()

+

+	e, err := db.get(name)

+	if err != nil {

+		return nil, err

+	}

+	return db.parents(e)

+}

+

 // Return the refrence count for a specified id

 func (db *Database) Refs(id string) int {

 	db.mux.RLock()

@@ -466,6 +478,28 @@ func (db *Database) children(e *Entity, name string, depth int, entities []WalkM

 	return entities, nil

 }

+func (db *Database) parents(e *Entity) (parents []string, err error) {

+	if e == nil {

+		return parents, nil

+	}

+

+	rows, err := db.conn.Query("SELECT parent_id FROM edge where entity_id = ?;", e.id)

+	if err != nil {

+		return nil, err

+	}

+	defer rows.Close()

+

+	for rows.Next() {

+		var parentId string

+		if err := rows.Scan(&parentId); err != nil {

+			return nil, err

+		}

+		parents = append(parents, parentId)

+	}

+

+	return parents, nil

+}

+

 // Return the entity based on the parent path and name

 func (db *Database) child(parent *Entity, name string) *Entity {

 	var id string

@@ -34,7 +34,7 @@ func TestNewDatabase(t *testing.T) {

 	defer destroyTestDb(dbpath)

 }

-func TestCreateRootEnity(t *testing.T) {

+func TestCreateRootEntity(t *testing.T) {

 	db, dbpath := newTestDb(t)

 	defer destroyTestDb(dbpath)

 	root := db.RootEntity()

@@ -94,6 +94,84 @@ func TestCreateChild(t *testing.T) {

 	}

 }

+func TestParents(t *testing.T) {

+	db, dbpath := newTestDb(t)

+	defer destroyTestDb(dbpath)

+

+	for i := 1; i < 6; i++ {

+		a := strconv.Itoa(i)

+		if _, err := db.Set("/"+a, a); err != nil {

+			t.Fatal(err)

+		}

+	}

+

+	for i := 6; i < 11; i++ {

+		a := strconv.Itoa(i)

+		p := strconv.Itoa(i - 5)

+

+		key := fmt.Sprintf("/%s/%s", p, a)

+

+		if _, err := db.Set(key, a); err != nil {

+			t.Fatal(err)

+		}

+

+		parents, err := db.Parents(key)

+		if err != nil {

+			t.Fatal(err)

+		}

+

+		if len(parents) != 1 {

+			t.Fatalf("Expected 2 entries for %s got %d", key, len(parents))

+		}

+

+		if parents[0] != p {

+			t.Fatalf("ID %s received, %s expected", parents[0], p)

+		}

+	}

+}

+

+func TestChildren(t *testing.T) {

+	db, dbpath := newTestDb(t)

+	defer destroyTestDb(dbpath)

+

+	str := "/"

+	for i := 1; i < 6; i++ {

+		a := strconv.Itoa(i)

+		if _, err := db.Set(str+a, a); err != nil {

+			t.Fatal(err)

+		}

+

+		str = str + a + "/"

+	}

+

+	str = "/"

+	for i := 10; i < 30; i++ { // 20 entities

+		a := strconv.Itoa(i)

+		if _, err := db.Set(str+a, a); err != nil {

+			t.Fatal(err)

+		}

+

+		str = str + a + "/"

+	}

+	entries, err := db.Children("/", 5)

+	if err != nil {

+		t.Fatal(err)

+	}

+

+	if len(entries) != 11 {

+		t.Fatalf("Expect 11 entries for / got %d", len(entries))

+	}

+

+	entries, err = db.Children("/", 20)

+	if err != nil {

+		t.Fatal(err)

+	}

+

+	if len(entries) != 25 {

+		t.Fatalf("Expect 25 entries for / got %d", len(entries))

+	}

+}

+

 func TestListAllRootChildren(t *testing.T) {

 	db, dbpath := newTestDb(t)

 	defer destroyTestDb(dbpath)

@@ -4,6 +4,7 @@ import (

 	"bytes"

 	"fmt"

 	"io/ioutil"

+	"regexp"

 )

 var defaultContent = map[string]string{

@@ -41,3 +42,12 @@ func Build(path, IP, hostname, domainname string, extraContent *map[string]strin

 	return ioutil.WriteFile(path, content.Bytes(), 0644)

 }

+

+func Update(path, IP, hostname string) error {

+	old, err := ioutil.ReadFile(path)

+	if err != nil {

+		return err

+	}

+	var re = regexp.MustCompile(fmt.Sprintf("(\\S*)(\\t%s)", regexp.QuoteMeta(hostname)))

+	return ioutil.WriteFile(path, re.ReplaceAll(old, []byte(IP+"$2")), 0644)

+}

@@ -72,3 +72,37 @@ func TestBuildNoIP(t *testing.T) {

 		t.Fatalf("Expected to find '%s' got '%s'", expected, content)

 	}

 }

+

+func TestUpdate(t *testing.T) {

+	file, err := ioutil.TempFile("", "")

+	if err != nil {

+		t.Fatal(err)

+	}

+	defer os.Remove(file.Name())

+

+	if err := Build(file.Name(), "10.11.12.13", "testhostname", "testdomainname", nil); err != nil {

+		t.Fatal(err)

+	}

+

+	content, err := ioutil.ReadFile(file.Name())

+	if err != nil {

+		t.Fatal(err)

+	}

+

+	if expected := "10.11.12.13\ttesthostname.testdomainname testhostname\n"; !bytes.Contains(content, []byte(expected)) {

+		t.Fatalf("Expected to find '%s' got '%s'", expected, content)

+	}

+

+	if err := Update(file.Name(), "1.1.1.1", "testhostname"); err != nil {

+		t.Fatal(err)

+	}

+

+	content, err = ioutil.ReadFile(file.Name())

+	if err != nil {

+		t.Fatal(err)

+	}

+

+	if expected := "1.1.1.1\ttesthostname.testdomainname testhostname\n"; !bytes.Contains(content, []byte(expected)) {

+		t.Fatalf("Expected to find '%s' got '%s'", expected, content)

+	}

+}