Merge pull request #225 from grayluck/externalname

Fix external name not solving by reloading resolv.conf.
kubernetes · Apr 16, 2018 · 80fdd88 · 80fdd88
2 parents 6df9916 + 969920f
commit 80fdd88
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Showing 3 changed files with 65 additions and 3 deletions.
diff --git a/cmd/kube-dns/app/server.go b/cmd/kube-dns/app/server.go
@@ -71,7 +71,11 @@ func NewKubeDNSServerDefault(config *options.KubeDNSConfig) *KubeDNSServer {
 
 	default:
 		glog.V(0).Infof("ConfigMap and ConfigDir not configured, using values from command line flags")
-		configSync = dnsconfig.NewNopSync(&dnsconfig.Config{Federations: config.Federations, UpstreamNameservers: strings.Split(config.NameServers, ",")})
+		conf := dnsconfig.Config{Federations: config.Federations}
+		if len(config.NameServers) > 0 {
+			conf.UpstreamNameservers = strings.Split(config.NameServers, ",")
+		}
+		configSync = dnsconfig.NewNopSync(&conf)
 	}
 
 	return &KubeDNSServer{

diff --git a/pkg/dns/dns.go b/pkg/dns/dns.go
@@ -53,6 +53,10 @@ const (
 	resyncPeriod = 5 * time.Minute
 )
 
+var (
+	defaultResolvFile = "/etc/resolv.conf"
+)
+
 type KubeDNS struct {
 	// kubeClient makes calls to API Server and registers calls with API Server
 	// to get Endpoints and Service objects.
@@ -139,6 +143,19 @@ func NewKubeDNS(client clientset.Interface, clusterDomain string, timeout time.D
 	return kd
 }
 
+func (kd *KubeDNS) loadDefaultNameserver() []string {
+	if c, err := dns.ClientConfigFromFile(defaultResolvFile); err != nil {
+		glog.Errorf("Load nameserver from resolv.conf failed: %v", err)
+		return []string{}
+	} else {
+		nameservers := []string{}
+		for _, s := range c.Servers {
+			nameservers = append(nameservers, net.JoinHostPort(s, c.Port))
+		}
+		return nameservers
+	}
+}
+
 func (kd *KubeDNS) updateConfig(nextConfig *config.Config) {
 	kd.configLock.Lock()
 	defer kd.configLock.Unlock()
@@ -147,13 +164,21 @@ func (kd *KubeDNS) updateConfig(nextConfig *config.Config) {
 		var nameServers []string
 		for _, nameServer := range nextConfig.UpstreamNameservers {
 			if ip, port, err := util.ValidateNameserverIpAndPort(nameServer); err != nil {
-				glog.V(1).Infof("Invalid nameserver %q: %v", nameServer, err)
+				glog.Errorf("Invalid nameserver %q: %v", nameServer, err)
+				if len(kd.SkyDNSConfig.Nameservers) == 0 {
+					// Fall back to resolv.conf on initialization failure.
+					kd.SkyDNSConfig.Nameservers = kd.loadDefaultNameserver()
+				}
 				return
 			} else {
 				nameServers = append(nameServers, net.JoinHostPort(ip, port))
 			}
 		}
-		kd.SkyDNSConfig.Nameservers = nameServers
+		if len(nameServers) == 0 {
+			kd.SkyDNSConfig.Nameservers = kd.loadDefaultNameserver()
+		} else {
+			kd.SkyDNSConfig.Nameservers = nameServers
+		}
 	}
 	kd.config = nextConfig
 	glog.V(2).Infof("Configuration updated: %+v", *kd.config)

diff --git a/pkg/dns/dns_test.go b/pkg/dns/dns_test.go
@@ -18,7 +18,10 @@ package dns
 
 import (
 	"fmt"
+	"io/ioutil"
 	"net"
+	"os"
+	"path/filepath"
 	"reflect"
 	"strings"
 	"sync"
@@ -702,6 +705,36 @@ func TestConfigSyncInitialMap(t *testing.T) {
 	checkConfigEqual(t, kd, &config.Config{Federations: map[string]string{"name3": "domain3"}})
 }
 
+func TestUpdateConfig(t *testing.T) {
+	tmpdir, err := ioutil.TempDir("", "test")
+	defaultResolvFile = filepath.Join(tmpdir, "resolv.conf")
+	require.NoError(t, err)
+	defer os.RemoveAll(tmpdir)
+
+	kd := newKubeDNS()
+	kd.SkyDNSConfig = new(skyserver.Config)
+
+	nextConfig := &config.Config{UpstreamNameservers: []string{"badNameserver"}}
+	kd.updateConfig(nextConfig)
+	assert.NotEqual(t, nextConfig, kd.config)
+	assert.Equal(t, []string{}, kd.SkyDNSConfig.Nameservers)
+
+	err = ioutil.WriteFile(defaultResolvFile, []byte("nameserver 127.0.0.1"), 0666)
+	require.NoError(t, err)
+
+	kd.updateConfig(nextConfig)
+	assert.Equal(t, []string{"127.0.0.1:53"}, kd.SkyDNSConfig.Nameservers)
+
+	nextConfig = &config.Config{UpstreamNameservers: []string{"192.0.2.123:10086", "192.0.2.123"}}
+	kd.updateConfig(nextConfig)
+	assert.Equal(t, nextConfig, kd.config)
+	assert.Equal(t, []string{"192.0.2.123:10086", "192.0.2.123:53"}, kd.SkyDNSConfig.Nameservers)
+
+	nextConfig = new(config.Config)
+	kd.updateConfig(nextConfig)
+	assert.Equal(t, []string{"127.0.0.1:53"}, kd.SkyDNSConfig.Nameservers)
+}
+
 func newNodes() *v1.NodeList {
 	return &v1.NodeList{
 		Items: []v1.Node{