Restore graceful shutdown of DNS server

Restore signal handling and graceful shutdown of DNS that had been added in
commit c802e22 but was subsequently lost
during rebase in commit 564ee03.

Graceful shutdown is necessary to ensure that when OpenShift's DNS server
shuts down, we remove it from the dnsmasq configuration.

This commit fixes bug 1624448.

https://bugzilla.redhat.com/show_bug.cgi?id=1624448

Author: Miciah

pkg/cmd/server/start/start_network.go

@@ -7,17 +7,18 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	"github.com/coreos/go-systemd/daemon"
 	"github.com/golang/glog"
 	"github.com/openshift/origin/pkg/cmd/server/origin"
 	"github.com/spf13/cobra"
 
 	kerrors "k8s.io/apimachinery/pkg/api/errors"
-	"k8s.io/apimachinery/pkg/util/wait"
 	"k8s.io/kubernetes/pkg/kubectl/cmd/templates"
 	kcmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
 	"k8s.io/kubernetes/pkg/master/ports"
+	"k8s.io/kubernetes/pkg/util/interrupt"
 
 	configapi "github.com/openshift/origin/pkg/cmd/server/apis/config"
 	configapilatest "github.com/openshift/origin/pkg/cmd/server/apis/config/latest"
@@ -57,7 +58,16 @@ func NewCommandStartNetwork(basename string, out, errout io.Writer) (*cobra.Comm
 		Short: "Launch node network",
 		Long:  fmt.Sprintf(networkLong, basename),
 		Run: func(c *cobra.Command, args []string) {
-			options.Run(c, errout, args, wait.NeverStop)
+			ch := make(chan struct{})
+			interrupt.New(func(s os.Signal) {
+				close(ch)
+				fmt.Fprintf(errout, "interrupt: Gracefully shutting down ...\n")
+				time.Sleep(200 * time.Millisecond)
+				os.Exit(1)
+			}).Run(func() error {
+				options.Run(c, errout, args, ch)
+				return nil
+			})
 		},
 	}
 
@@ -112,9 +122,10 @@ func (o NetworkOptions) Complete(cmd *cobra.Command) error {
 	return nil
 }
 
-// StartNode calls RunNode and then waits forever
+// StartNetwork starts the networking processes and then waits until the stop
+// channel receives a message or is closed.
 func (o NetworkOptions) StartNetwork(stopCh <-chan struct{}) error {
-	if err := o.RunNetwork(); err != nil {
+	if err := o.RunNetwork(stopCh); err != nil {
 		return err
 	}
 
@@ -123,10 +134,10 @@ func (o NetworkOptions) StartNetwork(stopCh <-chan struct{}) error {
 	return nil
 }
 
-// RunNetwork takes the options and:
-// 1.  Reads fully specified node config
-// 2.  Starts the node based on the fully specified config
-func (o NetworkOptions) RunNetwork() error {
+// RunNetwork takes the network options and does the following:
+// 1. Reads the fully specified node config.
+// 2. Starts the node networking based on the fully specified config.
+func (o NetworkOptions) RunNetwork(stopCh <-chan struct{}) error {
 	nodeConfig, configFile, err := o.resolveNodeConfig()
 	if err != nil {
 		return err
@@ -175,7 +186,7 @@ func (o NetworkOptions) RunNetwork() error {
 		return err
 	}
 
-	return StartNetwork(*nodeConfig, o.NodeArgs.Components)
+	return StartNetwork(*nodeConfig, o.NodeArgs.Components, stopCh)
 }
 
 // resolveNodeConfig creates a new configuration on disk by reading from the master, reads
@@ -191,8 +202,8 @@ func (o NetworkOptions) resolveNodeConfig() (*configapi.NodeConfig, string, erro
 	return cfg, o.ConfigFile, err
 }
 
-// StartNetwork launches the node processes.
-func StartNetwork(nodeConfig configapi.NodeConfig, components *utilflags.ComponentFlag) error {
+// StartNetwork launches the node networking processes.
+func StartNetwork(nodeConfig configapi.NodeConfig, components *utilflags.ComponentFlag, stopCh <-chan struct{}) error {
 	glog.Infof("Starting node networking %s (%s)", nodeConfig.NodeName, version.Get().String())
 
 	proxyConfig, err := networkoptions.Build(nodeConfig)
@@ -217,12 +228,12 @@ func StartNetwork(nodeConfig configapi.NodeConfig, components *utilflags.Compone
 		networkConfig.RunProxy()
 	}
 	if components.Enabled(ComponentDNS) && networkConfig.DNSServer != nil {
-		networkConfig.RunDNS(wait.NeverStop)
+		networkConfig.RunDNS(stopCh)
 	}
 
-	networkConfig.InternalKubeInformers.Start(wait.NeverStop)
+	networkConfig.InternalKubeInformers.Start(stopCh)
 	if networkConfig.NetworkInformers != nil {
-		networkConfig.NetworkInformers.Start(wait.NeverStop)
+		networkConfig.NetworkInformers.Start(stopCh)
 	}
 
 	return nil