Check /etc/resolv.conf every time for 127.* content

Currently if you start the docker -d on a system with 127.0.0.1 in /etc/resolv.conf
It will set the default dns to 8.8.8.8 8.8.4.4 permanently.

This causes a problem at boot on Fedora machines where NetworkManager has not
populated /etc/resolv.conf before docker gets started.

This fix checks /etc/resolv.conf on every docker run. And only populates
daemon.config.Dns  if the user specified it on the command line.

Docker-DCO-1.1-Signed-off-by: Dan Walsh <dwalsh@redhat.com> (github: rhatdan)

daemon/container.go

@@ -1,6 +1,7 @@
 package daemon
 
 import (
+	"bytes"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -918,22 +919,33 @@ func (container *Container) setupContainerDns() error {
 		return err
 	}
 
-	if config.NetworkMode != "host" && (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
+	if config.NetworkMode != "host" {
+		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)
+		} else {
+			resolvConf = utils.RemoveLocalDns(resolvConf)
+			if !bytes.Contains(resolvConf, []byte("nameserver")) {
+				for _, dns := range DefaultDns {
+					log.Infof("No non localhost DNS resolver found in resolv.conf and containers can't use it. Using default external servers : %v", DefaultDns)
+					resolvConf = append(append(resolvConf, []byte("\nnameserver ")...), dns...)
+				}
+				resolvConf = append(resolvConf, []byte("\n")...)
+			}
 		}
-		return resolvconf.Build(container.ResolvConfPath, dns, dnsSearch)
 	}
 	return ioutil.WriteFile(container.ResolvConfPath, resolvConf, 0644)
 }

daemon/daemon.go

@@ -1,7 +1,6 @@
 package daemon
 
 import (
-	"bytes"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -32,7 +31,6 @@ import (
 	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/docker/pkg/log"
 	"github.com/docker/docker/pkg/namesgenerator"
-	"github.com/docker/docker/pkg/networkfs/resolvconf"
 	"github.com/docker/docker/pkg/parsers"
 	"github.com/docker/docker/pkg/parsers/kernel"
 	"github.com/docker/docker/pkg/sysinfo"
@@ -925,9 +923,6 @@ func NewDaemonFromDirectory(config *Config, eng *engine.Engine) (*Daemon, error)
 		eng:            eng,
 		trustStore:     t,
 	}
-	if err := daemon.checkLocaldns(); err != nil {
-		return nil, err
-	}
 	if err := daemon.restore(); err != nil {
 		return nil, err
 	}
@@ -1087,20 +1082,6 @@ func (daemon *Daemon) ContainerGraph() *graphdb.Database {
 	return daemon.containerGraph
 }
 
-func (daemon *Daemon) checkLocaldns() error {
-	resolvConf, err := resolvconf.Get()
-	if err != nil {
-		return err
-	}
-	resolvConf = utils.RemoveLocalDns(resolvConf)
-
-	if len(daemon.config.Dns) == 0 && !bytes.Contains(resolvConf, []byte("nameserver")) {
-		log.Infof("No non localhost DNS resolver found in resolv.conf and containers can't use it. Using default external servers : %v", DefaultDns)
-		daemon.config.Dns = DefaultDns
-	}
-	return nil
-}
-
 func (daemon *Daemon) ImageGetCached(imgID string, config *runconfig.Config) (*image.Image, error) {
 	// Retrieve all images
 	images, err := daemon.Graph().Map()