func (ep *endpoint) setupDNS() error {
	ep.Lock()
	container := ep.container
	joinInfo := ep.joinInfo
	ep.Unlock()

	if container == nil {
		return ErrNoContainer{}
	}

	if container.config.resolvConfPath == "" {
		container.config.resolvConfPath = defaultPrefix + "/" + container.id + "/resolv.conf"
	}

	dir, _ := filepath.Split(container.config.resolvConfPath)
	err := createBasePath(dir)
	if err != nil {
		return err
	}

	if joinInfo.resolvConfPath != "" {
		if err := copyFile(joinInfo.resolvConfPath, container.config.resolvConfPath); err != nil {
			return fmt.Errorf("could not copy source resolv.conf file %s to %s: %v", joinInfo.resolvConfPath, container.config.resolvConfPath, err)
		}

		return nil
	}

	resolvConf, err := resolvconf.Get()
	if err != nil {
		return err
	}

	if len(container.config.dnsList) > 0 ||
		len(container.config.dnsSearchList) > 0 {
		var (
			dnsList       = resolvconf.GetNameservers(resolvConf)
			dnsSearchList = resolvconf.GetSearchDomains(resolvConf)
		)

		if len(container.config.dnsList) > 0 {
			dnsList = container.config.dnsList
		}

		if len(container.config.dnsSearchList) > 0 {
			dnsSearchList = container.config.dnsSearchList
		}

		return resolvconf.Build(container.config.resolvConfPath, dnsList, dnsSearchList)
	}

	return ep.updateDNS(resolvConf)
}

func (sb *sandbox) setupDNS() error {
	if sb.config.resolvConfPath == "" {
		sb.config.resolvConfPath = defaultPrefix + "/" + sb.id + "/resolv.conf"
	}

	sb.config.resolvConfHashFile = sb.config.resolvConfPath + ".hash"

	dir, _ := filepath.Split(sb.config.resolvConfPath)
	if err := createBasePath(dir); err != nil {
		return err
	}

	// This is for the host mode networking
	if sb.config.originResolvConfPath != "" {
		if err := copyFile(sb.config.originResolvConfPath, sb.config.resolvConfPath); err != nil {
			return fmt.Errorf("could not copy source resolv.conf file %s to %s: %v", sb.config.originResolvConfPath, sb.config.resolvConfPath, err)
		}
		return nil
	}

	resolvConf, err := resolvconf.Get()
	if err != nil {
		return err
	}
	dnsList := resolvconf.GetNameservers(resolvConf)
	dnsSearchList := resolvconf.GetSearchDomains(resolvConf)
	dnsOptionsList := resolvconf.GetOptions(resolvConf)

	if len(sb.config.dnsList) > 0 || len(sb.config.dnsSearchList) > 0 || len(dnsOptionsList) > 0 {
		if len(sb.config.dnsList) > 0 {
			dnsList = sb.config.dnsList
		}
		if len(sb.config.dnsSearchList) > 0 {
			dnsSearchList = sb.config.dnsSearchList
		}
		if len(sb.config.dnsOptionsList) > 0 {
			dnsOptionsList = sb.config.dnsOptionsList
		}
	}

	hash, err := resolvconf.Build(sb.config.resolvConfPath, dnsList, dnsSearchList, dnsOptionsList)
	if err != nil {
		return err
	}

	// write hash
	if err := ioutil.WriteFile(sb.config.resolvConfHashFile, []byte(hash), filePerm); err != nil {
		return types.InternalErrorf("failed to write resol.conf hash file when setting up dns for sandbox %s: %v", sb.ID(), err)
	}

	return nil
}

// Embedded DNS server has to be enabled for this sandbox. Rebuild the container's
// resolv.conf by doing the following
// - Save the external name servers in resolv.conf in the sandbox
// - Add only the embedded server's IP to container's resolv.conf
// - If the embedded server needs any resolv.conf options add it to the current list
func (sb *sandbox) rebuildDNS() error {
	currRC, err := resolvconf.GetSpecific(sb.config.resolvConfPath)
	if err != nil {
		return err
	}

	// localhost entries have already been filtered out from the list
	// retain only the v4 servers in sb for forwarding the DNS queries
	sb.extDNS = resolvconf.GetNameservers(currRC.Content, types.IPv4)

	var (
		dnsList        = []string{sb.resolver.NameServer()}
		dnsOptionsList = resolvconf.GetOptions(currRC.Content)
		dnsSearchList  = resolvconf.GetSearchDomains(currRC.Content)
	)

	// external v6 DNS servers has to be listed in resolv.conf
	dnsList = append(dnsList, resolvconf.GetNameservers(currRC.Content, types.IPv6)...)

	// If the user config and embedded DNS server both have ndots option set,
	// remember the user's config so that unqualified names not in the docker
	// domain can be dropped.
	resOptions := sb.resolver.ResolverOptions()

dnsOpt:
	for _, resOpt := range resOptions {
		if strings.Contains(resOpt, "ndots") {
			for _, option := range dnsOptionsList {
				if strings.Contains(option, "ndots") {
					parts := strings.Split(option, ":")
					if len(parts) != 2 {
						return fmt.Errorf("invalid ndots option %v", option)
					}
					if num, err := strconv.Atoi(parts[1]); err != nil {
						return fmt.Errorf("invalid number for ndots option %v", option)
					} else if num > 0 {
						sb.ndotsSet = true
						break dnsOpt
					}
				}
			}
		}
	}

	dnsOptionsList = append(dnsOptionsList, resOptions...)

	_, err = resolvconf.Build(sb.config.resolvConfPath, dnsList, dnsSearchList, dnsOptionsList)
	return err
}

func (ep *endpoint) setupDNS() error {
	ep.Lock()
	container := ep.container
	ep.Unlock()

	if container == nil {
		return ErrNoContainer{}
	}

	if container.config.resolvConfPath == "" {
		container.config.resolvConfPath = defaultPrefix + "/" + container.id + "/resolv.conf"
	}

	dir, _ := filepath.Split(container.config.resolvConfPath)
	err := createBasePath(dir)
	if err != nil {
		return err
	}

	resolvConf, err := resolvconf.Get()
	if err != nil {
		return err
	}

	if len(container.config.dnsList) > 0 ||
		len(container.config.dnsSearchList) > 0 {
		var (
			dnsList       = resolvconf.GetNameservers(resolvConf)
			dnsSearchList = resolvconf.GetSearchDomains(resolvConf)
		)

		if len(container.config.dnsList) > 0 {
			dnsList = container.config.dnsList
		}

		if len(container.config.dnsSearchList) > 0 {
			dnsSearchList = container.config.dnsSearchList
		}

		return resolvconf.Build(container.config.resolvConfPath, dnsList, dnsSearchList)
	}

	return ep.updateDNS(resolvConf)
}

// Embedded DNS server has to be enabled for this sandbox. Rebuild the container's
// resolv.conf by doing the follwing
// - Save the external name servers in resolv.conf in the sandbox
// - Add only the embedded server's IP to container's resolv.conf
// - If the embedded server needs any resolv.conf options add it to the current list
func (sb *sandbox) rebuildDNS() error {
	currRC, err := resolvconf.GetSpecific(sb.config.resolvConfPath)
	if err != nil {
		return err
	}

	// localhost entries have already been filtered out from the list
	sb.extDNS = resolvconf.GetNameservers(currRC.Content)

	var (
		dnsList        = []string{sb.resolver.NameServer()}
		dnsOptionsList = resolvconf.GetOptions(currRC.Content)
		dnsSearchList  = resolvconf.GetSearchDomains(currRC.Content)
	)

	// Resolver returns the options in the format resolv.conf expects
	dnsOptionsList = append(dnsOptionsList, sb.resolver.ResolverOptions()...)

	dir := path.Dir(sb.config.resolvConfPath)
	tmpResolvFile, err := ioutil.TempFile(dir, "resolv")
	if err != nil {
		return err
	}

	// Change the perms to filePerm (0644) since ioutil.TempFile creates it by default as 0600
	if err := os.Chmod(tmpResolvFile.Name(), filePerm); err != nil {
		return err
	}

	_, err = resolvconf.Build(tmpResolvFile.Name(), dnsList, dnsSearchList, dnsOptionsList)
	if err != nil {
		return err
	}

	return os.Rename(tmpResolvFile.Name(), sb.config.resolvConfPath)
}

func (sb *sandbox) setupDNS() error {
	var newRC *resolvconf.File

	if sb.config.resolvConfPath == "" {
		sb.config.resolvConfPath = defaultPrefix + "/" + sb.id + "/resolv.conf"
	}

	sb.config.resolvConfHashFile = sb.config.resolvConfPath + ".hash"

	dir, _ := filepath.Split(sb.config.resolvConfPath)
	if err := createBasePath(dir); err != nil {
		return err
	}

	// This is for the host mode networking
	if sb.config.originResolvConfPath != "" {
		if err := copyFile(sb.config.originResolvConfPath, sb.config.resolvConfPath); err != nil {
			return fmt.Errorf("could not copy source resolv.conf file %s to %s: %v", sb.config.originResolvConfPath, sb.config.resolvConfPath, err)
		}
		return nil
	}

	currRC, err := resolvconf.Get()
	if err != nil {
		return err
	}

	if len(sb.config.dnsList) > 0 || len(sb.config.dnsSearchList) > 0 || len(sb.config.dnsOptionsList) > 0 {
		var (
			err            error
			dnsList        = resolvconf.GetNameservers(currRC.Content, types.IP)
			dnsSearchList  = resolvconf.GetSearchDomains(currRC.Content)
			dnsOptionsList = resolvconf.GetOptions(currRC.Content)
		)
		if len(sb.config.dnsList) > 0 {
			dnsList = sb.config.dnsList
		}
		if len(sb.config.dnsSearchList) > 0 {
			dnsSearchList = sb.config.dnsSearchList
		}
		if len(sb.config.dnsOptionsList) > 0 {
			dnsOptionsList = sb.config.dnsOptionsList
		}
		newRC, err = resolvconf.Build(sb.config.resolvConfPath, dnsList, dnsSearchList, dnsOptionsList)
		if err != nil {
			return err
		}
		// After building the resolv.conf from the user config save the
		// external resolvers in the sandbox. Note that --dns 127.0.0.x
		// config refers to the loopback in the container namespace
		sb.setExternalResolvers(newRC.Content, types.IPv4, false)
	} else {
		// If the host resolv.conf file has 127.0.0.x container should
		// use the host restolver for queries. This is supported by the
		// docker embedded DNS server. Hence save the external resolvers
		// before filtering it out.
		sb.setExternalResolvers(currRC.Content, types.IPv4, true)

		// Replace any localhost/127.* (at this point we have no info about ipv6, pass it as true)
		if newRC, err = resolvconf.FilterResolvDNS(currRC.Content, true); err != nil {
			return err
		}
		// No contention on container resolv.conf file at sandbox creation
		if err := ioutil.WriteFile(sb.config.resolvConfPath, newRC.Content, filePerm); err != nil {
			return types.InternalErrorf("failed to write unhaltered resolv.conf file content when setting up dns for sandbox %s: %v", sb.ID(), err)
		}
	}

	// Write hash
	if err := ioutil.WriteFile(sb.config.resolvConfHashFile, []byte(newRC.Hash), filePerm); err != nil {
		return types.InternalErrorf("failed to write resolv.conf hash file when setting up dns for sandbox %s: %v", sb.ID(), err)
	}

	return nil
}