Set /etc/hostname.

Signed-off-by: Lantao Liu <lantaol@google.com>

integration/pod_hostname_test.go

@@ -28,7 +28,7 @@ import (
 	runtime "k8s.io/kubernetes/pkg/kubelet/apis/cri/runtime/v1alpha2"
 )
 
-func TestPodHostnameEnv(t *testing.T) {
+func TestPodHostname(t *testing.T) {
 	hostname, err := os.Hostname()
 	require.NoError(t, err)
 	for name, test := range map[string]struct {
@@ -56,13 +56,13 @@ func TestPodHostnameEnv(t *testing.T) {
 		},
 	} {
 		t.Run(name, func(t *testing.T) {
-			testPodLogDir, err := ioutil.TempDir("/tmp", "hostname-env")
+			testPodLogDir, err := ioutil.TempDir("/tmp", "hostname")
 			require.NoError(t, err)
 			defer os.RemoveAll(testPodLogDir)
 
 			opts := append(test.opts, WithPodLogDirectory(testPodLogDir))
 			t.Log("Create a sandbox with hostname")
-			sbConfig := PodSandboxConfig("sandbox", "hostname-env", opts...)
+			sbConfig := PodSandboxConfig("sandbox", "hostname", opts...)
 			sb, err := runtimeService.RunPodSandbox(sbConfig, *runtimeHandler)
 			require.NoError(t, err)
 			defer func() {
@@ -85,7 +85,8 @@ func TestPodHostnameEnv(t *testing.T) {
 			cnConfig := ContainerConfig(
 				containerName,
 				testImage,
-				WithCommand("env"),
+				WithCommand("sh", "-c",
+					"echo -n /etc/hostname= && cat /etc/hostname && env"),
 				WithLogPath(containerName),
 			)
 			cn, err := runtimeService.CreateContainer(sb, cnConfig, sbConfig)
@@ -106,10 +107,14 @@ func TestPodHostnameEnv(t *testing.T) {
 				return false, nil
 			}, time.Second, 30*time.Second))
 
-			t.Log("Search hostname env in container log")
 			content, err := ioutil.ReadFile(filepath.Join(testPodLogDir, containerName))
 			assert.NoError(t, err)
+
+			t.Log("Search hostname env in container log")
 			assert.Contains(t, string(content), "HOSTNAME="+test.expectedHostname)
+
+			t.Log("Search /etc/hostname content in container log")
+			assert.Contains(t, string(content), "/etc/hostname="+test.expectedHostname)
 		})
 	}
 }

pkg/server/container_create.go

@@ -339,8 +339,7 @@ func (c *criService) generateContainerSpec(id string, sandboxID string, sandboxP
 
 	// Add HOSTNAME env.
 	hostname := sandboxConfig.GetHostname()
-	if sandboxConfig.GetLinux().GetSecurityContext().GetNamespaceOptions().GetNetwork() == runtime.NamespaceMode_NODE &&
+	if sandboxConfig.GetHostname() == "" {
-		hostname == "" {
 		hostname, err = c.os.Hostname()
 		if err != nil {
 			return nil, err
@@ -483,6 +482,14 @@ func (c *criService) generateVolumeMounts(containerRootDir string, criMounts []*
 func (c *criService) generateContainerMounts(sandboxID string, config *runtime.ContainerConfig) []*runtime.Mount {
 	var mounts []*runtime.Mount
 	securityContext := config.GetLinux().GetSecurityContext()
+	if !isInCRIMounts(etcHostname, config.GetMounts()) {
+		mounts = append(mounts, &runtime.Mount{
+			ContainerPath: etcHostname,
+			HostPath:      c.getSandboxHostname(sandboxID),
+			Readonly:      securityContext.GetReadonlyRootfs(),
+		})
+	}
+
 	if !isInCRIMounts(etcHosts, config.GetMounts()) {
 		mounts = append(mounts, &runtime.Mount{
 			ContainerPath: etcHosts,

pkg/server/container_create_test.go

@@ -534,6 +534,11 @@ func TestGenerateContainerMounts(t *testing.T) {
 				ReadonlyRootfs: true,
 			},
 			expectedMounts: []*runtime.Mount{
+				{
+					ContainerPath: "/etc/hostname",
+					HostPath:      filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hostname"),
+					Readonly:      true,
+				},
 				{
 					ContainerPath: "/etc/hosts",
 					HostPath:      filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hosts"),
@@ -554,6 +559,11 @@ func TestGenerateContainerMounts(t *testing.T) {
 		"should setup rw mount when rootfs is read-write": {
 			securityContext: &runtime.LinuxContainerSecurityContext{},
 			expectedMounts: []*runtime.Mount{
+				{
+					ContainerPath: "/etc/hostname",
+					HostPath:      filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hostname"),
+					Readonly:      false,
+				},
 				{
 					ContainerPath: "/etc/hosts",
 					HostPath:      filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hosts"),
@@ -576,6 +586,11 @@ func TestGenerateContainerMounts(t *testing.T) {
 				NamespaceOptions: &runtime.NamespaceOption{Ipc: runtime.NamespaceMode_NODE},
 			},
 			expectedMounts: []*runtime.Mount{
+				{
+					ContainerPath: "/etc/hostname",
+					HostPath:      filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hostname"),
+					Readonly:      false,
+				},
 				{
 					ContainerPath: "/etc/hosts",
 					HostPath:      filepath.Join(testRootDir, sandboxesDir, testSandboxID, "hosts"),
@@ -595,6 +610,10 @@ func TestGenerateContainerMounts(t *testing.T) {
 		},
 		"should skip container mounts if already mounted by CRI": {
 			criMounts: []*runtime.Mount{
+				{
+					ContainerPath: "/etc/hostname",
+					HostPath:      "/test-etc-hostname",
+				},
 				{
 					ContainerPath: "/etc/hosts",
 					HostPath:      "/test-etc-host",

pkg/server/helpers.go

@@ -99,6 +99,8 @@ const (
 	devShm = "/dev/shm"
 	// etcHosts is the default path of /etc/hosts file.
 	etcHosts = "/etc/hosts"
+	// etcHostname is the default path of /etc/hostname file.
+	etcHostname = "/etc/hostname"
 	// resolvConfPath is the abs path of resolv.conf on host or container.
 	resolvConfPath = "/etc/resolv.conf"
 	// hostnameEnv is the key for HOSTNAME env.
@@ -199,6 +201,11 @@ func (c *criService) getVolatileContainerRootDir(id string) string {
 	return filepath.Join(c.config.StateDir, containersDir, id)
 }
 
+// getSandboxHostname returns the hostname file path inside the sandbox root directory.
+func (c *criService) getSandboxHostname(id string) string {
+	return filepath.Join(c.getSandboxRootDir(id), "hostname")
+}
+
 // getSandboxHosts returns the hosts file path inside the sandbox root directory.
 func (c *criService) getSandboxHosts(id string) string {
 	return filepath.Join(c.getSandboxRootDir(id), "hosts")

pkg/server/sandbox_run.go

@@ -233,7 +233,7 @@ func (c *criService) RunPodSandbox(ctx context.Context, r *runtime.RunPodSandbox
 		}
 	}()
 
-	// Setup sandbox /dev/shm, /etc/hosts and /etc/resolv.conf.
+	// Setup sandbox /dev/shm, /etc/hosts, /etc/resolv.conf and /etc/hostname.
 	if err = c.setupSandboxFiles(id, config); err != nil {
 		return nil, errors.Wrapf(err, "failed to setup sandbox files")
 	}
@@ -456,9 +456,22 @@ func (c *criService) generateSandboxContainerSpec(id string, config *runtime.Pod
 	return g.Config, nil
 }
 
-// setupSandboxFiles sets up necessary sandbox files including /dev/shm, /etc/hosts
+// setupSandboxFiles sets up necessary sandbox files including /dev/shm, /etc/hosts,
-// and /etc/resolv.conf.
+// /etc/resolv.conf and /etc/hostname.
 func (c *criService) setupSandboxFiles(id string, config *runtime.PodSandboxConfig) error {
+	sandboxEtcHostname := c.getSandboxHostname(id)
+	hostname := config.GetHostname()
+	if hostname == "" {
+		var err error
+		hostname, err = c.os.Hostname()
+		if err != nil {
+			return errors.Wrap(err, "failed to get hostname")
+		}
+	}
+	if err := c.os.WriteFile(sandboxEtcHostname, []byte(hostname+"\n"), 0644); err != nil {
+		return errors.Wrapf(err, "failed to write hostname to %q", sandboxEtcHostname)
+	}
+
 	// TODO(random-liu): Consider whether we should maintain /etc/hosts and /etc/resolv.conf in kubelet.
 	sandboxEtcHosts := c.getSandboxHosts(id)
 	if err := c.os.CopyFile(etcHosts, sandboxEtcHosts, 0644); err != nil {

pkg/server/sandbox_run_test.go

@@ -180,15 +180,30 @@ func TestGenerateSandboxContainerSpec(t *testing.T) {
 }
 
 func TestSetupSandboxFiles(t *testing.T) {
-	const testID = "test-id"
+	const (
+		testID       = "test-id"
+		realhostname = "test-real-hostname"
+	)
 	for desc, test := range map[string]struct {
 		dnsConfig     *runtime.DNSConfig
+		hostname      string
 		ipcMode       runtime.NamespaceMode
 		expectedCalls []ostesting.CalledDetail
 	}{
 		"should check host /dev/shm existence when ipc mode is NODE": {
 			ipcMode: runtime.NamespaceMode_NODE,
 			expectedCalls: []ostesting.CalledDetail{
+				{
+					Name: "Hostname",
+				},
+				{
+					Name: "WriteFile",
+					Arguments: []interface{}{
+						filepath.Join(testRootDir, sandboxesDir, testID, "hostname"),
+						[]byte(realhostname + "\n"),
+						os.FileMode(0644),
+					},
+				},
 				{
 					Name: "CopyFile",
 					Arguments: []interface{}{
@@ -219,6 +234,17 @@ func TestSetupSandboxFiles(t *testing.T) {
 			},
 			ipcMode: runtime.NamespaceMode_NODE,
 			expectedCalls: []ostesting.CalledDetail{
+				{
+					Name: "Hostname",
+				},
+				{
+					Name: "WriteFile",
+					Arguments: []interface{}{
+						filepath.Join(testRootDir, sandboxesDir, testID, "hostname"),
+						[]byte(realhostname + "\n"),
+						os.FileMode(0644),
+					},
+				},
 				{
 					Name: "CopyFile",
 					Arguments: []interface{}{
@@ -246,6 +272,17 @@ options timeout:1
 		"should create sandbox shm when ipc namespace mode is not NODE": {
 			ipcMode: runtime.NamespaceMode_POD,
 			expectedCalls: []ostesting.CalledDetail{
+				{
+					Name: "Hostname",
+				},
+				{
+					Name: "WriteFile",
+					Arguments: []interface{}{
+						filepath.Join(testRootDir, sandboxesDir, testID, "hostname"),
+						[]byte(realhostname + "\n"),
+						os.FileMode(0644),
+					},
+				},
 				{
 					Name: "CopyFile",
 					Arguments: []interface{}{
@@ -275,10 +312,48 @@ options timeout:1
 				},
 			},
 		},
+		"should create /etc/hostname when hostname is set": {
+			hostname: "test-hostname",
+			ipcMode:  runtime.NamespaceMode_NODE,
+			expectedCalls: []ostesting.CalledDetail{
+				{
+					Name: "WriteFile",
+					Arguments: []interface{}{
+						filepath.Join(testRootDir, sandboxesDir, testID, "hostname"),
+						[]byte("test-hostname\n"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name: "CopyFile",
+					Arguments: []interface{}{
+						"/etc/hosts",
+						filepath.Join(testRootDir, sandboxesDir, testID, "hosts"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name: "CopyFile",
+					Arguments: []interface{}{
+						"/etc/resolv.conf",
+						filepath.Join(testRootDir, sandboxesDir, testID, "resolv.conf"),
+						os.FileMode(0644),
+					},
+				},
+				{
+					Name:      "Stat",
+					Arguments: []interface{}{"/dev/shm"},
+				},
+			},
+		},
 	} {
 		t.Logf("TestCase %q", desc)
 		c := newTestCRIService()
+		c.os.(*ostesting.FakeOS).HostnameFn = func() (string, error) {
+			return realhostname, nil
+		}
 		cfg := &runtime.PodSandboxConfig{
+			Hostname:  test.hostname,
 			DnsConfig: test.dnsConfig,
 			Linux: &runtime.LinuxPodSandboxConfig{
 				SecurityContext: &runtime.LinuxSandboxSecurityContext{