Add option for node-cache to reload in-process CoreDNS via a signal.

cmd/node-cache/app/cache_app.go

@@ -14,6 +14,7 @@ limitations under the License.
 package app
 
 import (
+	"fmt"
 	"net"
 	"os"
 	"strings"
@@ -52,6 +53,7 @@ type ConfigParams struct {
 	HealthPort           string        // port for the healthcheck
 	SetupIptables        bool
 	SkipTeardown         bool // Indicates whether the iptables rules and interface should be torn down
+	ReloadWithSignal     bool // Indicates config reload should be triggered with SIGUSR1, rather than expecting CoreDNS's reload plugin
 }
 
 type iptablesRule struct {
@@ -69,6 +71,7 @@ type CacheApp struct {
 	kubednsConfig *options.KubeDNSConfig
 	exitChan      chan struct{} // Channel to terminate background goroutines
 	clusterDNSIP  net.IP
+	selfProcess   *os.Process
 }
 
 func isLockedErr(err error) bool {
@@ -277,6 +280,13 @@ func (c *CacheApp) RunApp() {
 // NewCacheApp returns a new instance of CacheApp by applying the specified config params.
 func NewCacheApp(params *ConfigParams) (*CacheApp, error) {
 	c := &CacheApp{params: params, kubednsConfig: options.NewKubeDNSConfig()}
+	if params.ReloadWithSignal {
+		var err error
+		c.selfProcess, err = os.FindProcess(os.Getpid())
+		if err != nil {
+			return nil, fmt.Errorf("failed to get process handle on self: %w", err)
+		}
+	}
 	c.clusterDNSIP = net.ParseIP(os.ExpandEnv(toSvcEnv(params.UpstreamSvcName)))
 	if c.clusterDNSIP == nil {
 		clog.Warningf("Unable to lookup IP address of Upstream service %s, env %s `%s`", params.UpstreamSvcName, toSvcEnv(params.UpstreamSvcName), os.ExpandEnv(toSvcEnv(params.UpstreamSvcName)))

cmd/node-cache/app/configmap.go

@@ -18,6 +18,7 @@ import (
 	"os"
 	"path"
 	"strings"
+	"syscall"
 	"text/template"
 	"time"
 
@@ -132,6 +133,14 @@ func (c *CacheApp) updateCorefile(dnsConfig *config.Config) {
 	}
 	clog.Infof("Updated Corefile with %d custom stubdomains and upstream servers %s", len(dnsConfig.StubDomains), upstreamServers)
 	clog.Infof("Using config file:\n%s", newConfig.String())
+
+	// Trigger reload of in-process CoreDNS
+	if c.selfProcess != nil {
+		clog.Infof("Sending reload signal to PID %v", c.selfProcess.Pid)
+		if err := c.selfProcess.Signal(syscall.SIGUSR1); err != nil {
+			clog.Errorf("Failed to trigger CoreDNS reload: %v", err)
+		}
+	}
 }
 
 // syncInfo contains all parameters needed to watch a configmap directory for updates

cmd/node-cache/main.go

@@ -90,6 +90,7 @@ func parseAndValidateFlags() (*app.ConfigParams, error) {
 	flag.StringVar(&params.UpstreamSvcName, "upstreamsvc", "kube-dns", "Service name whose cluster IP is upstream for node-cache")
 	flag.StringVar(&params.HealthPort, "health-port", "8080", "port used by health plugin")
 	flag.BoolVar(&params.SkipTeardown, "skipteardown", false, "indicates whether iptables rules should be torn down on exit")
+	flag.BoolVar(&params.ReloadWithSignal, "reloadwithsignal", false, "use SIGUSR1 on self to reload CoreDNS")
 	flag.Parse()
 
 	for _, ipstr := range strings.Split(params.LocalIPStr, ",") {