// set up the watch on the host's /etc/resolv.conf so that we can update container's
// live resolv.conf when the network changes on the host
func (daemon *Daemon) setupResolvconfWatcher() error {
watcher, err := fsnotify.NewWatcher()
if err != nil {
return err
}
//this goroutine listens for the events on the watch we add
//on the resolv.conf file on the host
go func() {
for {
select {
case event := <-watcher.Events:
if event.Name == "/etc/resolv.conf" &&
(event.Op&fsnotify.Write == fsnotify.Write ||
event.Op&fsnotify.Create == fsnotify.Create) {
// verify a real change happened before we go further--a file write may have happened
// without an actual change to the file
updatedResolvConf, newResolvConfHash, err := resolvconf.GetIfChanged()
if err != nil {
log.Debugf("Error retrieving updated host resolv.conf: %v", err)
} else if updatedResolvConf != nil {
// because the new host resolv.conf might have localhost nameservers..
updatedResolvConf, modified := resolvconf.FilterResolvDns(updatedResolvConf, daemon.config.EnableIPv6)
if modified {
// changes have occurred during localhost cleanup: generate an updated hash
newHash, err := utils.HashData(bytes.NewReader(updatedResolvConf))
if err != nil {
log.Debugf("Error generating hash of new resolv.conf: %v", err)
} else {
newResolvConfHash = newHash
}
}
log.Debugf("host network resolv.conf changed--walking container list for updates")
contList := daemon.containers.List()
for _, container := range contList {
if err := container.updateResolvConf(updatedResolvConf, newResolvConfHash); err != nil {
log.Debugf("Error on resolv.conf update check for container ID: %s: %v", container.ID, err)
}
}
}
}
case err := <-watcher.Errors:
log.Debugf("host resolv.conf notify error: %v", err)
}
}
}()
if err := watcher.Add("/etc"); err != nil {
return err
}
return nil
}
// GetIfChanged retrieves the host /etc/resolv.conf file, checks against the last hash
// and, if modified since last check, returns the bytes and new hash.
// This feature is used by the resolv.conf updater for containers
func GetIfChanged() ([]byte, string, error) {
lastModified.Lock()
defer lastModified.Unlock()
resolv, err := ioutil.ReadFile("/etc/resolv.conf")
if err != nil {
return nil, "", err
}
newHash, err := utils.HashData(bytes.NewReader(resolv))
if err != nil {
return nil, "", err
}
if lastModified.sha256 != newHash {
lastModified.sha256 = newHash
lastModified.contents = resolv
return resolv, newHash, nil
}
// nothing changed, so return no data
return nil, "", nil
}
// called when the host's resolv.conf changes to check whether container's resolv.conf
// is unchanged by the container "user" since container start: if unchanged, the
// container's resolv.conf will be updated to match the host's new resolv.conf
func (container *Container) updateResolvConf(updatedResolvConf []byte, newResolvHash string) error {
if container.ResolvConfPath == "" {
return nil
}
if container.Running {
//set a marker in the hostConfig to update on next start/restart
container.UpdateDns = true
return nil
}
resolvHashFile := container.ResolvConfPath + ".hash"
//read the container's current resolv.conf and compute the hash
resolvBytes, err := ioutil.ReadFile(container.ResolvConfPath)
if err != nil {
return err
}
curHash, err := utils.HashData(bytes.NewReader(resolvBytes))
if err != nil {
return err
}
//read the hash from the last time we wrote resolv.conf in the container
hashBytes, err := ioutil.ReadFile(resolvHashFile)
if err != nil {
if !os.IsNotExist(err) {
return err
}
// backwards compat: if no hash file exists, this container pre-existed from
// a Docker daemon that didn't contain this update feature. Given we can't know
// if the user has modified the resolv.conf since container start time, safer
// to just never update the container's resolv.conf during it's lifetime which
// we can control by setting hashBytes to an empty string
hashBytes = []byte("")
}
//if the user has not modified the resolv.conf of the container since we wrote it last
//we will replace it with the updated resolv.conf from the host
if string(hashBytes) == curHash {
log.Debugf("replacing %q with updated host resolv.conf", container.ResolvConfPath)
// for atomic updates to these files, use temporary files with os.Rename:
dir := path.Dir(container.ResolvConfPath)
tmpHashFile, err := ioutil.TempFile(dir, "hash")
if err != nil {
return err
}
tmpResolvFile, err := ioutil.TempFile(dir, "resolv")
if err != nil {
return err
}
// write the updates to the temp files
if err = ioutil.WriteFile(tmpHashFile.Name(), []byte(newResolvHash), 0644); err != nil {
return err
}
if err = ioutil.WriteFile(tmpResolvFile.Name(), updatedResolvConf, 0644); err != nil {
return err
}
// rename the temp files for atomic replace
if err = os.Rename(tmpHashFile.Name(), resolvHashFile); err != nil {
return err
}
return os.Rename(tmpResolvFile.Name(), container.ResolvConfPath)
}
return nil
}
func (container *Container) setupContainerDns() error {
if container.ResolvConfPath != "" {
// check if this is an existing container that needs DNS update:
if container.UpdateDns {
// read the host's resolv.conf, get the hash and call updateResolvConf
log.Debugf("Check container (%s) for update to resolv.conf - UpdateDns flag was set", container.ID)
latestResolvConf, latestHash := resolvconf.GetLastModified()
// clean container resolv.conf re: localhost nameservers and IPv6 NS (if IPv6 disabled)
updatedResolvConf, modified := resolvconf.FilterResolvDns(latestResolvConf, container.daemon.config.EnableIPv6)
if modified {
// changes have occurred during resolv.conf localhost cleanup: generate an updated hash
newHash, err := utils.HashData(bytes.NewReader(updatedResolvConf))
if err != nil {
return err
}
latestHash = newHash
}
if err := container.updateResolvConf(updatedResolvConf, latestHash); err != nil {
return err
}
// successful update of the restarting container; set the flag off
container.UpdateDns = false
}
return nil
}
var (
config = container.hostConfig
daemon = container.daemon
)
resolvConf, err := resolvconf.Get()
if err != nil {
return err
}
container.ResolvConfPath, err = container.getRootResourcePath("resolv.conf")
if err != nil {
return err
}
if config.NetworkMode != "host" {
// check configurations for any container/daemon dns settings
if len(config.Dns) > 0 || len(daemon.config.Dns) > 0 || len(config.DnsSearch) > 0 || len(daemon.config.DnsSearch) > 0 {
var (
dns = resolvconf.GetNameservers(resolvConf)
dnsSearch = resolvconf.GetSearchDomains(resolvConf)
)
if len(config.Dns) > 0 {
dns = config.Dns
} else if len(daemon.config.Dns) > 0 {
dns = daemon.config.Dns
}
if len(config.DnsSearch) > 0 {
dnsSearch = config.DnsSearch
} else if len(daemon.config.DnsSearch) > 0 {
dnsSearch = daemon.config.DnsSearch
}
return resolvconf.Build(container.ResolvConfPath, dns, dnsSearch)
}
// replace any localhost/127.*, and remove IPv6 nameservers if IPv6 disabled in daemon
resolvConf, _ = resolvconf.FilterResolvDns(resolvConf, daemon.config.EnableIPv6)
}
//get a sha256 hash of the resolv conf at this point so we can check
//for changes when the host resolv.conf changes (e.g. network update)
resolvHash, err := utils.HashData(bytes.NewReader(resolvConf))
if err != nil {
return err
}
resolvHashFile := container.ResolvConfPath + ".hash"
if err = ioutil.WriteFile(resolvHashFile, []byte(resolvHash), 0644); err != nil {
return err
}
return ioutil.WriteFile(container.ResolvConfPath, resolvConf, 0644)
}