Merge pull request #177 from inercia/inercia/registries_skip_warning

[Enhancement] Do not print the /etc/hosts message if the registry name can be resolved (thanks @inercia )

cli/commands.go

@@ -10,6 +10,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/docker/docker/api/types"
 	"github.com/docker/docker/api/types/filters"
@@ -270,7 +271,9 @@ func CreateCluster(c *cli.Context) error {
 	 * Registry (optional)
 	 * Create the (optional) registry container
 	 */
+	var registryNameExists *dnsNameCheck
 	if clusterSpec.RegistryEnabled {
+		registryNameExists = newAsyncNameExists(clusterSpec.RegistryName, 1*time.Second)
 		if _, err = createRegistry(*clusterSpec); err != nil {
 			deleteCluster()
 			return err
@@ -325,7 +328,11 @@ func CreateCluster(c *cli.Context) error {
 
 	if clusterSpec.RegistryEnabled {
 		log.Printf("A local registry has been started as %s:%d", clusterSpec.RegistryName, clusterSpec.RegistryPort)
-		log.Printf("Make sure you have an alias in your /etc/hosts file like '127.0.0.1 %s'", clusterSpec.RegistryName)
+
+		exists, err := registryNameExists.Exists()
+		if !exists || err != nil {
+			log.Printf("Make sure you have an alias in your /etc/hosts file like '127.0.0.1 %s'", clusterSpec.RegistryName)
+		}
 	}
 
 	log.Printf(`You can now use the cluster with:

cli/util.go

@@ -126,3 +126,36 @@ func fileExists(filename string) bool {
 	_, err := os.Stat(filename)
 	return !os.IsNotExist(err)
 }
+
+type dnsNameCheck struct {
+	res     chan bool
+	err     chan error
+	timeout time.Duration
+}
+
+func newAsyncNameExists(name string, timeout time.Duration) *dnsNameCheck {
+	d := &dnsNameCheck{
+		res:     make(chan bool),
+		err:     make(chan error),
+		timeout: timeout,
+	}
+	go func() {
+		addresses, err := net.LookupHost(name)
+		if err != nil {
+			d.err <- err
+		}
+		d.res <- len(addresses) > 0
+	}()
+	return d
+}
+
+func (d dnsNameCheck) Exists() (bool, error) {
+	select {
+	case r := <-d.res:
+		return r, nil
+	case e := <-d.err:
+		return false, e
+	case <-time.After(d.timeout):
+		return false, nil
+	}
+}