Fixes #2820

config.go

@@ -27,8 +27,8 @@ func ConfigFromJob(job *engine.Job) *DaemonConfig {
 	config.Root = job.Getenv("Root")
 	config.AutoRestart = job.GetenvBool("AutoRestart")
 	config.EnableCors = job.GetenvBool("EnableCors")
-	if dns := job.Getenv("Dns"); dns != "" {
-		config.Dns = []string{dns}
+	if dns := job.GetenvList("Dns"); dns != nil {
+		config.Dns = dns
 	}
 	config.EnableIptables = job.GetenvBool("EnableIptables")
 	if br := job.Getenv("BridgeIface"); br != "" {

docker/docker.go

@@ -33,13 +33,14 @@ func main() {
 		pidfile              = flag.String("p", "/var/run/docker.pid", "Path to use for daemon PID file")
 		flRoot               = flag.String("g", "/var/lib/docker", "Path to use as the root of the docker runtime")
 		flEnableCors         = flag.Bool("api-enable-cors", false, "Enable CORS headers in the remote API")
-		flDns                = flag.String("dns", "", "Force docker to use specific DNS servers")
+		flDns                = docker.NewListOpts(docker.ValidateIp4Address)
 		flEnableIptables     = flag.Bool("iptables", true, "Disable docker's addition of iptables rules")
 		flDefaultIp          = flag.String("ip", "0.0.0.0", "Default IP address to use when binding container ports")
 		flInterContainerComm = flag.Bool("icc", true, "Enable inter-container communication")
 		flGraphDriver        = flag.String("s", "", "Force the docker runtime to use a specific storage driver")
 		flHosts              = docker.NewListOpts(docker.ValidateHost)
 	)
+	flag.Var(&flDns, "dns", "Force docker to use specific DNS servers")
 	flag.Var(&flHosts, "H", "Multiple tcp://host:port or unix://path/to/socket to bind in daemon mode, single connection otherwise")
 
 	flag.Parse()
@@ -73,7 +74,7 @@ func main() {
 		job.Setenv("Root", *flRoot)
 		job.SetenvBool("AutoRestart", *flAutoRestart)
 		job.SetenvBool("EnableCors", *flEnableCors)
-		job.Setenv("Dns", *flDns)
+		job.SetenvList("Dns", flDns.GetAll())
 		job.SetenvBool("EnableIptables", *flEnableIptables)
 		job.Setenv("BridgeIface", *bridgeName)
 		job.Setenv("DefaultIp", *flDefaultIp)

opts.go

@@ -5,6 +5,7 @@ import (
 	"github.com/dotcloud/docker/utils"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 )
 
@@ -134,3 +135,12 @@ func ValidateHost(val string) (string, error) {
 	}
 	return host, nil
 }
+
+func ValidateIp4Address(val string) (string, error) {
+	re := regexp.MustCompile(`^(([0-9]+\.){3}([0-9]+))\s*$`)
+	var ns = re.FindSubmatch([]byte(val))
+	if len(ns) > 0 {
+		return string(ns[1]), nil
+	}
+	return "", fmt.Errorf("%s is not an ip4 address", val)
+}