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Move exported constants/functions from dockertools to dockershim

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Previously we exported many constants and functions in dockertools to
share with the dockershim package. This change moves such
constants/functions to dockershim and unexport them.

This change involves only mechnical changes and should not have any
functional impact.
This commit is contained in:
Yu-Ju Hong
2017-05-01 17:17:19 -07:00
parent 93ecaf6812
commit b209f47562
5 changed files with 245 additions and 325 deletions
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22
pkg/kubelet/dockershim/docker_image.go
View File

@@ -17,6 +17,8 @@ limitations under the License.
package dockershim
import (
"fmt"
dockertypes "github.com/docker/engine-api/types"
runtimeapi "k8s.io/kubernetes/pkg/kubelet/api/v1alpha1/runtime"
"k8s.io/kubernetes/pkg/kubelet/dockertools"
@@ -80,7 +82,7 @@ func (ds *dockerService) PullImage(image *runtimeapi.ImageSpec, auth *runtimeapi
return "", err
}
return dockertools.GetImageRef(ds.client, image.Image)
return getImageRef(ds.client, image.Image)
}
// RemoveImage removes the image.
@@ -101,3 +103,21 @@ func (ds *dockerService) RemoveImage(image *runtimeapi.ImageSpec) error {
_, err = ds.client.RemoveImage(image.Image, dockertypes.ImageRemoveOptions{PruneChildren: true})
return err
}
// getImageRef returns the image digest if exists, or else returns the image ID.
func getImageRef(client dockertools.DockerInterface, image string) (string, error) {
img, err := client.InspectImageByRef(image)
if err != nil {
return "", err
}
if img == nil {
return "", fmt.Errorf("unable to inspect image %s", image)
}
// Returns the digest if it exist.
if len(img.RepoDigests) > 0 {
return img.RepoDigests[0], nil
}
return img.ID, nil
}

29
pkg/kubelet/dockershim/docker_service.go
View File

@@ -20,12 +20,14 @@ import (
"fmt"
"io"
"net/http"
"strconv"
"time"
"github.com/blang/semver"
dockertypes "github.com/docker/engine-api/types"
"github.com/golang/glog"
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
"k8s.io/kubernetes/pkg/api/v1"
"k8s.io/kubernetes/pkg/apis/componentconfig"
internalapi "k8s.io/kubernetes/pkg/kubelet/api"
@@ -489,7 +491,32 @@ func (d *dockerLegacyService) GetContainerLogs(pod *v1.Pod, containerID kubecont
if err != nil {
return err
}
return dockertools.GetContainerLogs(d.client, pod, containerID, logOptions, stdout, stderr, container.Config.Tty)
var since int64
if logOptions.SinceSeconds != nil {
t := metav1.Now().Add(-time.Duration(*logOptions.SinceSeconds) * time.Second)
since = t.Unix()
}
if logOptions.SinceTime != nil {
since = logOptions.SinceTime.Unix()
}
opts := dockertypes.ContainerLogsOptions{
ShowStdout: true,
ShowStderr: true,
Since: strconv.FormatInt(since, 10),
Timestamps: logOptions.Timestamps,
Follow: logOptions.Follow,
}
if logOptions.TailLines != nil {
opts.Tail = strconv.FormatInt(*logOptions.TailLines, 10)
}
sopts := dockertools.StreamOptions{
OutputStream: stdout,
ErrorStream: stderr,
RawTerminal: container.Config.Tty,
}
return d.client.Logs(containerID.ID, opts, sopts)
}
// criSupportedLogDrivers are log drivers supported by native CRI integration.

88
pkg/kubelet/dockershim/docker_streaming.go
View File

@@ -21,11 +21,15 @@ import (
"fmt"
"io"
"math"
"os/exec"
"strings"
"time"
dockertypes "github.com/docker/engine-api/types"
"github.com/golang/glog"
"k8s.io/kubernetes/pkg/client/unversioned/remotecommand"
runtimeapi "k8s.io/kubernetes/pkg/kubelet/api/v1alpha1/runtime"
kubecontainer "k8s.io/kubernetes/pkg/kubelet/container"
"k8s.io/kubernetes/pkg/kubelet/dockertools"
"k8s.io/kubernetes/pkg/kubelet/server/streaming"
"k8s.io/kubernetes/pkg/kubelet/util/ioutils"
@@ -57,14 +61,14 @@ func (r *streamingRuntime) Attach(containerID string, in io.Reader, out, errw io
return err
}
return dockertools.AttachContainer(r.client, containerID, in, out, errw, tty, resize)
return attachContainer(r.client, containerID, in, out, errw, tty, resize)
}
func (r *streamingRuntime) PortForward(podSandboxID string, port int32, stream io.ReadWriteCloser) error {
if port < 0 || port > math.MaxUint16 {
return fmt.Errorf("invalid port %d", port)
}
return dockertools.PortForward(r.client, podSandboxID, port, stream)
return portForward(r.client, podSandboxID, port, stream)
}
// ExecSync executes a command in the container, and returns the stdout output.
@@ -128,3 +132,83 @@ func checkContainerStatus(client dockertools.DockerInterface, containerID string
}
return container, nil
}
func attachContainer(client dockertools.DockerInterface, containerID string, stdin io.Reader, stdout, stderr io.WriteCloser, tty bool, resize <-chan remotecommand.TerminalSize) error {
// Have to start this before the call to client.AttachToContainer because client.AttachToContainer is a blocking
// call :-( Otherwise, resize events don't get processed and the terminal never resizes.
kubecontainer.HandleResizing(resize, func(size remotecommand.TerminalSize) {
client.ResizeContainerTTY(containerID, int(size.Height), int(size.Width))
})
// TODO(random-liu): Do we really use the *Logs* field here?
opts := dockertypes.ContainerAttachOptions{
Stream: true,
Stdin: stdin != nil,
Stdout: stdout != nil,
Stderr: stderr != nil,
}
sopts := dockertools.StreamOptions{
InputStream: stdin,
OutputStream: stdout,
ErrorStream: stderr,
RawTerminal: tty,
}
return client.AttachToContainer(containerID, opts, sopts)
}
func portForward(client dockertools.DockerInterface, podInfraContainerID string, port int32, stream io.ReadWriteCloser) error {
container, err := client.InspectContainer(podInfraContainerID)
if err != nil {
return err
}
if !container.State.Running {
return fmt.Errorf("container not running (%s)", container.ID)
}
containerPid := container.State.Pid
socatPath, lookupErr := exec.LookPath("socat")
if lookupErr != nil {
return fmt.Errorf("unable to do port forwarding: socat not found.")
}
args := []string{"-t", fmt.Sprintf("%d", containerPid), "-n", socatPath, "-", fmt.Sprintf("TCP4:localhost:%d", port)}
nsenterPath, lookupErr := exec.LookPath("nsenter")
if lookupErr != nil {
return fmt.Errorf("unable to do port forwarding: nsenter not found.")
}
commandString := fmt.Sprintf("%s %s", nsenterPath, strings.Join(args, " "))
glog.V(4).Infof("executing port forwarding command: %s", commandString)
command := exec.Command(nsenterPath, args...)
command.Stdout = stream
stderr := new(bytes.Buffer)
command.Stderr = stderr
// If we use Stdin, command.Run() won't return until the goroutine that's copying
// from stream finishes. Unfortunately, if you have a client like telnet connected
// via port forwarding, as long as the user's telnet client is connected to the user's
// local listener that port forwarding sets up, the telnet session never exits. This
// means that even if socat has finished running, command.Run() won't ever return
// (because the client still has the connection and stream open).
//
// The work around is to use StdinPipe(), as Wait() (called by Run()) closes the pipe
// when the command (socat) exits.
inPipe, err := command.StdinPipe()
if err != nil {
return fmt.Errorf("unable to do port forwarding: error creating stdin pipe: %v", err)
}
go func() {
io.Copy(inPipe, stream)
inPipe.Close()
}()
if err := command.Run(); err != nil {
return fmt.Errorf("%v: %s", err, stderr.String())
}
return nil
}

119
pkg/kubelet/dockershim/helpers.go
View File

@@ -17,7 +17,12 @@ limitations under the License.
package dockershim
import (
"bytes"
"crypto/md5"
"encoding/json"
"fmt"
"io/ioutil"
"path/filepath"
"regexp"
"strconv"
"strings"
@@ -28,14 +33,21 @@ import (
dockernat "github.com/docker/go-connections/nat"
"github.com/golang/glog"
"k8s.io/kubernetes/pkg/api/v1"
v1helper "k8s.io/kubernetes/pkg/api/v1/helper"
runtimeapi "k8s.io/kubernetes/pkg/kubelet/api/v1alpha1/runtime"
"k8s.io/kubernetes/pkg/kubelet/dockertools"
"k8s.io/kubernetes/pkg/kubelet/types"
"k8s.io/kubernetes/pkg/security/apparmor"
)
const (
annotationPrefix = "annotation."
// Docker changed the API for specifying options in v1.11
securityOptSeparatorChangeVersion = "1.23.0" // Corresponds to docker 1.11.x
securityOptSeparatorOld = ':'
securityOptSeparatorNew = '='
)
var (
@@ -43,7 +55,9 @@ var (
// Docker changes the security option separator from ':' to '=' in the 1.23
// API version.
optsSeparatorChangeVersion = semver.MustParse(dockertools.SecurityOptSeparatorChangeVersion)
optsSeparatorChangeVersion = semver.MustParse(securityOptSeparatorChangeVersion)
defaultSeccompOpt = []dockerOpt{{"seccomp", "unconfined", ""}}
)
// generateEnvList converts KeyValue list to a list of strings, in the form of
@@ -181,17 +195,57 @@ func makePortsAndBindings(pm []*runtimeapi.PortMapping) (map[dockernat.Port]stru
return exposedPorts, portBindings
}
func getSeccompDockerOpts(annotations map[string]string, ctrName, profileRoot string) ([]dockerOpt, error) {
profile, profileOK := annotations[v1.SeccompContainerAnnotationKeyPrefix+ctrName]
if !profileOK {
// try the pod profile
profile, profileOK = annotations[v1.SeccompPodAnnotationKey]
if !profileOK {
// return early the default
return defaultSeccompOpt, nil
}
}
if profile == "unconfined" {
// return early the default
return defaultSeccompOpt, nil
}
if profile == "docker/default" {
// return nil so docker will load the default seccomp profile
return nil, nil
}
if !strings.HasPrefix(profile, "localhost/") {
return nil, fmt.Errorf("unknown seccomp profile option: %s", profile)
}
name := strings.TrimPrefix(profile, "localhost/") // by pod annotation validation, name is a valid subpath
fname := filepath.Join(profileRoot, filepath.FromSlash(name))
file, err := ioutil.ReadFile(fname)
if err != nil {
return nil, fmt.Errorf("cannot load seccomp profile %q: %v", name, err)
}
b := bytes.NewBuffer(nil)
if err := json.Compact(b, file); err != nil {
return nil, err
}
// Rather than the full profile, just put the filename & md5sum in the event log.
msg := fmt.Sprintf("%s(md5:%x)", name, md5.Sum(file))
return []dockerOpt{{"seccomp", b.String(), msg}}, nil
}
// getSeccompSecurityOpts gets container seccomp options from container and sandbox
// config, currently from sandbox annotations.
// It is an experimental feature and may be promoted to official runtime api in the future.
func getSeccompSecurityOpts(containerName string, sandboxConfig *runtimeapi.PodSandboxConfig, seccompProfileRoot string, separator rune) ([]string, error) {
seccompOpts, err := dockertools.GetSeccompOpts(sandboxConfig.GetAnnotations(), containerName, seccompProfileRoot)
seccompOpts, err := getSeccompDockerOpts(sandboxConfig.GetAnnotations(), containerName, seccompProfileRoot)
if err != nil {
return nil, err
}
fmtOpts := dockertools.FmtDockerOpts(seccompOpts, separator)
return fmtOpts, nil
return fmtDockerOpts(seccompOpts, separator), nil
}
// getApparmorSecurityOpts gets apparmor options from container config.
@@ -200,12 +254,12 @@ func getApparmorSecurityOpts(sc *runtimeapi.LinuxContainerSecurityContext, separ
return nil, nil
}
appArmorOpts, err := dockertools.GetAppArmorOpts(sc.ApparmorProfile)
appArmorOpts, err := getAppArmorOpts(sc.ApparmorProfile)
if err != nil {
return nil, err
}
fmtOpts := dockertools.FmtDockerOpts(appArmorOpts, separator)
fmtOpts := fmtDockerOpts(appArmorOpts, separator)
return fmtOpts, nil
}
@@ -258,10 +312,23 @@ func (f *dockerFilter) AddLabel(key, value string) {
f.Add("label", fmt.Sprintf("%s=%s", key, value))
}
// parseUserFromImageUser splits the user out of an user:group string.
func parseUserFromImageUser(id string) string {
if id == "" {
return id
}
// split instances where the id may contain user:group
if strings.Contains(id, ":") {
return strings.Split(id, ":")[0]
}
// no group, just return the id
return id
}
// getUserFromImageUser gets uid or user name of the image user.
// If user is numeric, it will be treated as uid; or else, it is treated as user name.
func getUserFromImageUser(imageUser string) (*int64, string) {
user := dockertools.GetUserFromImageUser(imageUser)
user := parseUserFromImageUser(imageUser)
// return both nil if user is not specified in the image.
if user == "" {
return nil, ""
@@ -321,9 +388,9 @@ func getSecurityOptSeparator(v *semver.Version) rune {
case -1:
// Current version is less than the API change version; use the old
// separator.
return dockertools.SecurityOptSeparatorOld
return securityOptSeparatorOld
default:
return dockertools.SecurityOptSeparatorNew
return securityOptSeparatorNew
}
}
@@ -342,3 +409,35 @@ func ensureSandboxImageExists(client dockertools.DockerInterface, image string)
}
return nil
}
func getAppArmorOpts(profile string) ([]dockerOpt, error) {
if profile == "" || profile == apparmor.ProfileRuntimeDefault {
// The docker applies the default profile by default.
return nil, nil
}
// Assume validation has already happened.
profileName := strings.TrimPrefix(profile, apparmor.ProfileNamePrefix)
return []dockerOpt{{"apparmor", profileName, ""}}, nil
}
// fmtDockerOpts formats the docker security options using the given separator.
func fmtDockerOpts(opts []dockerOpt, sep rune) []string {
fmtOpts := make([]string, len(opts))
for i, opt := range opts {
fmtOpts[i] = fmt.Sprintf("%s%c%s", opt.key, sep, opt.value)
}
return fmtOpts
}
type dockerOpt struct {
// The key-value pair passed to docker.
key, value string
// The alternative value to use in log/event messages.
msg string
}
// Expose key/value from dockertools
func (d dockerOpt) GetKV() (string, string) {
return d.key, d.value
}

312
pkg/kubelet/dockertools/docker_manager.go
View File

@@ -16,38 +16,8 @@ limitations under the License.
package dockertools
import (
"bytes"
"crypto/md5"
"encoding/json"
"fmt"
"io"
"io/ioutil"
"os"
"os/exec"
"path/filepath"
"strconv"
"strings"
"time"
dockertypes "github.com/docker/engine-api/types"
"github.com/golang/glog"
metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
"k8s.io/kubernetes/pkg/api/v1"
"k8s.io/kubernetes/pkg/client/unversioned/remotecommand"
kubecontainer "k8s.io/kubernetes/pkg/kubelet/container"
"k8s.io/kubernetes/pkg/security/apparmor"
)
const (
DockerType = "docker"
dockerDefaultLoggingDriver = "json-file"
// Docker changed the API for specifying options in v1.11
SecurityOptSeparatorChangeVersion = "1.23.0" // Corresponds to docker 1.11.x
SecurityOptSeparatorOld = ':'
SecurityOptSeparatorNew = '='
DockerType = "docker"
// https://docs.docker.com/engine/reference/api/docker_remote_api/
// docker version should be at least 1.10.x
@@ -56,284 +26,4 @@ const (
statusRunningPrefix = "Up"
statusExitedPrefix = "Exited"
statusCreatedPrefix = "Created"
ndotsDNSOption = "options ndots:5\n"
)
var (
defaultSeccompOpt = []dockerOpt{{"seccomp", "unconfined", ""}}
)
// GetImageRef returns the image digest if exists, or else returns the image ID.
// It is exported for reusing in dockershim.
func GetImageRef(client DockerInterface, image string) (string, error) {
img, err := client.InspectImageByRef(image)
if err != nil {
return "", err
}
if img == nil {
return "", fmt.Errorf("unable to inspect image %s", image)
}
// Returns the digest if it exist.
if len(img.RepoDigests) > 0 {
return img.RepoDigests[0], nil
}
return img.ID, nil
}
// Temporarily export this function to share with dockershim.
// TODO: clean this up.
func GetContainerLogs(client DockerInterface, pod *v1.Pod, containerID kubecontainer.ContainerID, logOptions *v1.PodLogOptions, stdout, stderr io.Writer, rawTerm bool) error {
var since int64
if logOptions.SinceSeconds != nil {
t := metav1.Now().Add(-time.Duration(*logOptions.SinceSeconds) * time.Second)
since = t.Unix()
}
if logOptions.SinceTime != nil {
since = logOptions.SinceTime.Unix()
}
opts := dockertypes.ContainerLogsOptions{
ShowStdout: true,
ShowStderr: true,
Since: strconv.FormatInt(since, 10),
Timestamps: logOptions.Timestamps,
Follow: logOptions.Follow,
}
if logOptions.TailLines != nil {
opts.Tail = strconv.FormatInt(*logOptions.TailLines, 10)
}
sopts := StreamOptions{
OutputStream: stdout,
ErrorStream: stderr,
RawTerminal: rawTerm,
}
return client.Logs(containerID.ID, opts, sopts)
}
// Temporarily export this function to share with dockershim.
// TODO: clean this up.
func AttachContainer(client DockerInterface, containerID string, stdin io.Reader, stdout, stderr io.WriteCloser, tty bool, resize <-chan remotecommand.TerminalSize) error {
// Have to start this before the call to client.AttachToContainer because client.AttachToContainer is a blocking
// call :-( Otherwise, resize events don't get processed and the terminal never resizes.
kubecontainer.HandleResizing(resize, func(size remotecommand.TerminalSize) {
client.ResizeContainerTTY(containerID, int(size.Height), int(size.Width))
})
// TODO(random-liu): Do we really use the *Logs* field here?
opts := dockertypes.ContainerAttachOptions{
Stream: true,
Stdin: stdin != nil,
Stdout: stdout != nil,
Stderr: stderr != nil,
}
sopts := StreamOptions{
InputStream: stdin,
OutputStream: stdout,
ErrorStream: stderr,
RawTerminal: tty,
}
return client.AttachToContainer(containerID, opts, sopts)
}
// Temporarily export this function to share with dockershim.
func PortForward(client DockerInterface, podInfraContainerID string, port int32, stream io.ReadWriteCloser) error {
container, err := client.InspectContainer(podInfraContainerID)
if err != nil {
return err
}
if !container.State.Running {
return fmt.Errorf("container not running (%s)", container.ID)
}
containerPid := container.State.Pid
socatPath, lookupErr := exec.LookPath("socat")
if lookupErr != nil {
return fmt.Errorf("unable to do port forwarding: socat not found.")
}
args := []string{"-t", fmt.Sprintf("%d", containerPid), "-n", socatPath, "-", fmt.Sprintf("TCP4:localhost:%d", port)}
nsenterPath, lookupErr := exec.LookPath("nsenter")
if lookupErr != nil {
return fmt.Errorf("unable to do port forwarding: nsenter not found.")
}
commandString := fmt.Sprintf("%s %s", nsenterPath, strings.Join(args, " "))
glog.V(4).Infof("executing port forwarding command: %s", commandString)
command := exec.Command(nsenterPath, args...)
command.Stdout = stream
stderr := new(bytes.Buffer)
command.Stderr = stderr
// If we use Stdin, command.Run() won't return until the goroutine that's copying
// from stream finishes. Unfortunately, if you have a client like telnet connected
// via port forwarding, as long as the user's telnet client is connected to the user's
// local listener that port forwarding sets up, the telnet session never exits. This
// means that even if socat has finished running, command.Run() won't ever return
// (because the client still has the connection and stream open).
//
// The work around is to use StdinPipe(), as Wait() (called by Run()) closes the pipe
// when the command (socat) exits.
inPipe, err := command.StdinPipe()
if err != nil {
return fmt.Errorf("unable to do port forwarding: error creating stdin pipe: %v", err)
}
go func() {
io.Copy(inPipe, stream)
inPipe.Close()
}()
if err := command.Run(); err != nil {
return fmt.Errorf("%v: %s", err, stderr.String())
}
return nil
}
// Temporarily export this function to share with dockershim.
// TODO: clean this up.
func GetAppArmorOpts(profile string) ([]dockerOpt, error) {
if profile == "" || profile == apparmor.ProfileRuntimeDefault {
// The docker applies the default profile by default.
return nil, nil
}
// Assume validation has already happened.
profileName := strings.TrimPrefix(profile, apparmor.ProfileNamePrefix)
return []dockerOpt{{"apparmor", profileName, ""}}, nil
}
// Temporarily export this function to share with dockershim.
// TODO: clean this up.
func GetSeccompOpts(annotations map[string]string, ctrName, profileRoot string) ([]dockerOpt, error) {
profile, profileOK := annotations[v1.SeccompContainerAnnotationKeyPrefix+ctrName]
if !profileOK {
// try the pod profile
profile, profileOK = annotations[v1.SeccompPodAnnotationKey]
if !profileOK {
// return early the default
return defaultSeccompOpt, nil
}
}
if profile == "unconfined" {
// return early the default
return defaultSeccompOpt, nil
}
if profile == "docker/default" {
// return nil so docker will load the default seccomp profile
return nil, nil
}
if !strings.HasPrefix(profile, "localhost/") {
return nil, fmt.Errorf("unknown seccomp profile option: %s", profile)
}
name := strings.TrimPrefix(profile, "localhost/") // by pod annotation validation, name is a valid subpath
fname := filepath.Join(profileRoot, filepath.FromSlash(name))
file, err := ioutil.ReadFile(fname)
if err != nil {
return nil, fmt.Errorf("cannot load seccomp profile %q: %v", name, err)
}
b := bytes.NewBuffer(nil)
if err := json.Compact(b, file); err != nil {
return nil, err
}
// Rather than the full profile, just put the filename & md5sum in the event log.
msg := fmt.Sprintf("%s(md5:%x)", name, md5.Sum(file))
return []dockerOpt{{"seccomp", b.String(), msg}}, nil
}
// FmtDockerOpts formats the docker security options using the given separator.
func FmtDockerOpts(opts []dockerOpt, sep rune) []string {
fmtOpts := make([]string, len(opts))
for i, opt := range opts {
fmtOpts[i] = fmt.Sprintf("%s%c%s", opt.key, sep, opt.value)
}
return fmtOpts
}
type dockerOpt struct {
// The key-value pair passed to docker.
key, value string
// The alternative value to use in log/event messages.
msg string
}
// Expose key/value from dockertools
func (d dockerOpt) GetKV() (string, string) {
return d.key, d.value
}
// GetUserFromImageUser splits the user out of an user:group string.
func GetUserFromImageUser(id string) string {
if id == "" {
return id
}
// split instances where the id may contain user:group
if strings.Contains(id, ":") {
return strings.Split(id, ":")[0]
}
// no group, just return the id
return id
}
// RewriteResolvFile rewrites resolv.conf file generated by docker.
// Exported for reusing in dockershim.
func RewriteResolvFile(resolvFilePath string, dns []string, dnsSearch []string, useClusterFirstPolicy bool) error {
if len(resolvFilePath) == 0 {
glog.Errorf("ResolvConfPath is empty.")
return nil
}
if _, err := os.Stat(resolvFilePath); os.IsNotExist(err) {
return fmt.Errorf("ResolvConfPath %q does not exist", resolvFilePath)
}
var resolvFileContent []string
for _, srv := range dns {
resolvFileContent = append(resolvFileContent, "nameserver "+srv)
}
if len(dnsSearch) > 0 {
resolvFileContent = append(resolvFileContent, "search "+strings.Join(dnsSearch, " "))
}
if len(resolvFileContent) > 0 {
if useClusterFirstPolicy {
resolvFileContent = append(resolvFileContent, ndotsDNSOption)
}
resolvFileContentStr := strings.Join(resolvFileContent, "\n")
resolvFileContentStr += "\n"
glog.V(4).Infof("Will attempt to re-write config file %s with: \n%s", resolvFilePath, resolvFileContent)
if err := rewriteFile(resolvFilePath, resolvFileContentStr); err != nil {
glog.Errorf("resolv.conf could not be updated: %v", err)
return err
}
}
return nil
}
func rewriteFile(filePath, stringToWrite string) error {
f, err := os.OpenFile(filePath, os.O_TRUNC|os.O_WRONLY, 0644)
if err != nil {
return err
}
defer f.Close()
_, err = f.WriteString(stringToWrite)
return err
}