Merge pull request #11955 from pedro-r-marques/flag_resolv_conf

cmd/kubelet/app/server.go

@@ -123,6 +123,7 @@ type KubeletServer struct {
 	PodCIDR                        string
 	MaxPods                        int
 	DockerExecHandlerName          string
+	ResolverConfig                 string
 
 	// Flags intended for testing
 
@@ -253,6 +254,7 @@ func (s *KubeletServer) AddFlags(fs *pflag.FlagSet) {
 	fs.IntVar(&s.MaxPods, "max-pods", 40, "Number of Pods that can run on this Kubelet.")
 	fs.StringVar(&s.DockerExecHandlerName, "docker-exec-handler", s.DockerExecHandlerName, "Handler to use when executing a command in a container. Valid values are 'native' and 'nsenter'. Defaults to 'native'.")
 	fs.StringVar(&s.PodCIDR, "pod-cidr", "", "The CIDR to use for pod IP addresses, only used in standalone mode.  In cluster mode, this is obtained from the master.")
+	fs.StringVar(&s.ResolverConfig, "resolv-conf", kubelet.ResolvConfDefault, "Resolver configuration file used as the basis for the container DNS resolution configuration.")
 	// Flags intended for testing, not recommended used in production environments.
 	fs.BoolVar(&s.ReallyCrashForTesting, "really-crash-for-testing", s.ReallyCrashForTesting, "If true, when panics occur crash. Intended for testing.")
 	fs.Float64Var(&s.ChaosChance, "chaos-chance", s.ChaosChance, "If > 0.0, introduce random client errors and latency. Intended for testing. [default=0.0]")
@@ -359,6 +361,7 @@ func (s *KubeletServer) KubeletConfig() (*KubeletConfig, error) {
 		PodCIDR:                   s.PodCIDR,
 		MaxPods:                   s.MaxPods,
 		DockerExecHandler:         dockerExecHandler,
+		ResolverConfig:            s.ResolverConfig,
 	}, nil
 }
 
@@ -600,6 +603,7 @@ func SimpleKubelet(client *client.Client,
 		SystemContainer:           "",
 		MaxPods:                   32,
 		DockerExecHandler:         &dockertools.NativeExecHandler{},
+		ResolverConfig:            kubelet.ResolvConfDefault,
 	}
 	return &kcfg
 }
@@ -769,6 +773,7 @@ type KubeletConfig struct {
 	PodCIDR                        string
 	MaxPods                        int
 	DockerExecHandler              dockertools.ExecHandler
+	ResolverConfig                 string
 }
 
 func createAndInitKubelet(kc *KubeletConfig) (k KubeletBootstrap, pc *config.PodConfig, err error) {
@@ -827,7 +832,8 @@ func createAndInitKubelet(kc *KubeletConfig) (k KubeletBootstrap, pc *config.Pod
 		kc.ConfigureCBR0,
 		kc.PodCIDR,
 		kc.MaxPods,
-		kc.DockerExecHandler)
+		kc.DockerExecHandler,
+		kc.ResolverConfig)
 
 	if err != nil {
 		return nil, nil, err

contrib/mesos/pkg/executor/service/service.go

@@ -261,6 +261,7 @@ func (s *KubeletExecutorServer) Run(hks hyperkube.Interface, _ []string) error {
 		ConfigureCBR0:             s.ConfigureCBR0,
 		MaxPods:                   s.MaxPods,
 		DockerExecHandler:         dockerExecHandler,
+		ResolverConfig:            s.ResolverConfig,
 	}
 
 	kcfg.NodeName = kcfg.Hostname
@@ -362,6 +363,7 @@ func (ks *KubeletExecutorServer) createAndInitKubelet(
 		kc.PodCIDR,
 		kc.MaxPods,
 		kc.DockerExecHandler,
+		kc.ResolverConfig,
 	)
 	if err != nil {
 		return nil, nil, err

hack/verify-flags/known-flags.txt

@@ -206,6 +206,7 @@ reject-paths
 repo-root
 report-dir
 required-contexts
+resolv-conf
 resource-container
 resource-quota-sync-period
 resource-version

pkg/kubelet/kubelet.go

@@ -87,6 +87,9 @@ const (
 	// suffice because a goroutine is dedicated to check the channel and does
 	// not block on anything else.
 	podKillingChannelCapacity = 50
+
+	// system default DNS resolver configuration
+	ResolvConfDefault = "/etc/resolv.conf"
 )
 
 var (
@@ -159,7 +162,8 @@ func NewMainKubelet(
 	configureCBR0 bool,
 	podCIDR string,
 	pods int,
-	dockerExecHandler dockertools.ExecHandler) (*Kubelet, error) {
+	dockerExecHandler dockertools.ExecHandler,
+	resolverConfig string) (*Kubelet, error) {
 	if rootDirectory == "" {
 		return nil, fmt.Errorf("invalid root directory %q", rootDirectory)
 	}
@@ -275,6 +279,7 @@ func NewMainKubelet(
 		podCIDR:                        podCIDR,
 		pods:                           pods,
 		syncLoopMonitor:                util.AtomicValue{},
+		resolverConfig:                 resolverConfig,
 	}
 
 	if plug, err := network.InitNetworkPlugin(networkPlugins, networkPluginName, &networkHost{klet}); err != nil {
@@ -542,6 +547,11 @@ type Kubelet struct {
 
 	// Channel for sending pods to kill.
 	podKillingCh chan *kubecontainer.Pod
+
+	// The configuration file used as the base to generate the container's
+	// DNS resolver configuration file. This can be used in conjunction with
+	// clusterDomain and clusterDNS.
+	resolverConfig string
 }
 
 // getRootDir returns the full path to the directory under which kubelet can
@@ -948,12 +958,12 @@ func (kl *Kubelet) GenerateRunContainerOptions(pod *api.Pod, container *api.Cont
 			opts.PodContainerDir = p
 		}
 	}
-	if pod.Spec.DNSPolicy == api.DNSClusterFirst {
-		opts.DNS, opts.DNSSearch, err = kl.getClusterDNS(pod)
-		if err != nil {
-			return nil, err
-		}
+
+	opts.DNS, opts.DNSSearch, err = kl.getClusterDNS(pod)
+	if err != nil {
+		return nil, err
 	}
+
 	return opts, nil
 }
 
@@ -1086,27 +1096,47 @@ func (kl *Kubelet) podFieldSelectorRuntimeValue(fs *api.ObjectFieldSelector, pod
 // getClusterDNS returns a list of the DNS servers and a list of the DNS search
 // domains of the cluster.
 func (kl *Kubelet) getClusterDNS(pod *api.Pod) ([]string, []string, error) {
+	var hostDNS, hostSearch []string
 	// Get host DNS settings and append them to cluster DNS settings.
-	f, err := os.Open("/etc/resolv.conf")
-	if err != nil {
-		return nil, nil, err
-	}
-	defer f.Close()
+	if kl.resolverConfig != "" {
+		f, err := os.Open(kl.resolverConfig)
+		if err != nil {
+			return nil, nil, err
+		}
+		defer f.Close()
 
-	hostDNS, hostSearch, err := parseResolvConf(f)
-	if err != nil {
-		return nil, nil, err
+		hostDNS, hostSearch, err = parseResolvConf(f)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	if pod.Spec.DNSPolicy != api.DNSClusterFirst {
+		// When the kubelet --resolv-conf flag is set to the empty string, use
+		// DNS settings that override the docker default (which is to use
+		// /etc/resolv.conf) and effectivly disable DNS lookups. According to
+		// the bind documentation, the behavior of the DNS client library when
+		// "nameservers" are not specified is to "use the nameserver on the
+		// local machine". A nameserver setting of localhost is equivalent to
+		// this documented behavior.
+		if kl.resolverConfig == "" {
+			hostDNS = []string{"127.0.0.1"}
+			hostSearch = []string{"."}
+		}
+		return hostDNS, hostSearch, nil
 	}
-
 	var dns, dnsSearch []string
 
 	if kl.clusterDNS != nil {
 		dns = append([]string{kl.clusterDNS.String()}, hostDNS...)
+	} else {
+		dns = hostDNS
 	}
 	if kl.clusterDomain != "" {
 		nsSvcDomain := fmt.Sprintf("%s.svc.%s", pod.Namespace, kl.clusterDomain)
 		svcDomain := fmt.Sprintf("svc.%s", kl.clusterDomain)
 		dnsSearch = append([]string{nsSvcDomain, svcDomain, kl.clusterDomain}, hostSearch...)
+	} else {
+		dnsSearch = hostSearch
 	}
 	return dns, dnsSearch, nil
 }

pkg/kubelet/kubelet_test.go

@@ -22,6 +22,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"net"
 	"net/http"
 	"os"
 	"path"
@@ -874,6 +875,61 @@ func TestParseResolvConf(t *testing.T) {
 	}
 }
 
+func TestDNSConfigurationParams(t *testing.T) {
+	testKubelet := newTestKubelet(t)
+	kubelet := testKubelet.kubelet
+
+	clusterNS := "203.0.113.1"
+	kubelet.clusterDomain = "kubernetes.io"
+	kubelet.clusterDNS = net.ParseIP(clusterNS)
+
+	pods := newTestPods(2)
+	pods[0].Spec.DNSPolicy = api.DNSClusterFirst
+	pods[1].Spec.DNSPolicy = api.DNSDefault
+
+	options := make([]*kubecontainer.RunContainerOptions, 2)
+	for i, pod := range pods {
+		var err error
+		kubelet.volumeManager.SetVolumes(pod.UID, make(kubecontainer.VolumeMap, 0))
+		options[i], err = kubelet.GenerateRunContainerOptions(pod, &api.Container{})
+		if err != nil {
+			t.Fatalf("failed to generate container options: %v", err)
+		}
+	}
+	if len(options[0].DNS) != 1 || options[0].DNS[0] != clusterNS {
+		t.Errorf("expected nameserver %s, got %+v", clusterNS, options[0].DNS)
+	}
+	if len(options[0].DNSSearch) == 0 || options[0].DNSSearch[0] != ".svc."+kubelet.clusterDomain {
+		t.Errorf("expected search %s, got %+v", ".svc."+kubelet.clusterDomain, options[0].DNSSearch)
+	}
+	if len(options[1].DNS) != 1 || options[1].DNS[0] != "127.0.0.1" {
+		t.Errorf("expected nameserver 127.0.0.1, got %+v", options[1].DNS)
+	}
+	if len(options[1].DNSSearch) != 1 || options[1].DNSSearch[0] != "." {
+		t.Errorf("expected search \".\", got %+v", options[1].DNSSearch)
+	}
+
+	kubelet.resolverConfig = "/etc/resolv.conf"
+	for i, pod := range pods {
+		var err error
+		options[i], err = kubelet.GenerateRunContainerOptions(pod, &api.Container{})
+		if err != nil {
+			t.Fatalf("failed to generate container options: %v", err)
+		}
+	}
+	t.Logf("nameservers %+v", options[1].DNS)
+	if len(options[0].DNS) != len(options[1].DNS)+1 {
+		t.Errorf("expected prepend of cluster nameserver, got %+v", options[0].DNS)
+	} else if options[0].DNS[0] != clusterNS {
+		t.Errorf("expected nameserver %s, got %v", clusterNS, options[0].DNS[0])
+	}
+	if len(options[0].DNSSearch) != len(options[1].DNSSearch)+3 {
+		t.Errorf("expected prepend of cluster domain, got %+v", options[0].DNSSearch)
+	} else if options[0].DNSSearch[0] != ".svc."+kubelet.clusterDomain {
+		t.Errorf("expected domain %s, got %s", ".svc."+kubelet.clusterDomain, options[0].DNSSearch)
+	}
+}
+
 type testServiceLister struct {
 	services []api.Service
 }