feat(AM-6688): make kubeslice-dns as default dns server

Corefile

@@ -1,4 +1,6 @@
 .:1053 {
-  debug
+  log
   kubeslice
-}
+  forward . <ClusterIP of kube-dns>
+  reload 2s
+}

Dockerfile

@@ -19,7 +19,6 @@ FROM gcr.io/distroless/static:nonroot
 WORKDIR /
 
 COPY --from=builder /workspace/coredns .
-COPY Corefile Corefile
 
 USER nonroot:nonroot
 

plugin/kubeslice/handler.go

@@ -15,16 +15,17 @@ import (
 var log = clog.NewWithPlugin("kubeslice")
 
 // ServeDNS implements the plugin.Handler interface.
-func (ks Kubeslice) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
+func (ks *Kubeslice) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error) {
 	log.Debug("Question type", r.Question)
 
 	state := request.Request{W: w, Req: r}
 	zone := "slice.local"
 
-	records, truncated, err := plugin.A(ctx, &ks, zone, state, nil, plugin.Options{})
+	records, truncated, err := plugin.A(ctx, ks, zone, state, nil, plugin.Options{})
 
 	if err != nil {
-		return dns.RcodeServerFailure, err
+		log.Debug("query not answered,fallthrough forrward plugin")
+		return plugin.NextOrFailure(ks.Name(), ks.Next, ctx, w, r)
 	}
 
 	m := new(dns.Msg)
@@ -39,4 +40,4 @@ func (ks Kubeslice) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.M
 }
 
 // Name implements the Handler interface.
-func (e Kubeslice) Name() string { return "kubeslice" }
+func (e *Kubeslice) Name() string { return "kubeslice" }

plugin/kubeslice/kubeslice.go

@@ -2,6 +2,7 @@ package kubeslice
 
 import (
 	"context"
+	"errors"
 
 	"github.com/coredns/coredns/plugin/etcd/msg"
 	"github.com/coredns/coredns/request"
@@ -17,6 +18,10 @@ type Kubeslice struct {
 	EndpointsCache dnsCache.EndpointsCache
 }
 
+func New() *Kubeslice {
+	return &Kubeslice{}
+}
+
 func (ks *Kubeslice) Services(ctx context.Context, state request.Request, exact bool, opt plugin.Options) ([]msg.Service, error) {
 
 	var svcs []msg.Service
@@ -44,6 +49,9 @@ func (ks *Kubeslice) Services(ctx context.Context, state request.Request, exact
 			svcs = append(svcs, svc)
 		}
 	}
+	if len(svcs) == 0 {
+		return svcs, errors.New("no records found")
+	}
 
 	return svcs, nil
 

plugin/kubeslice/ready.go

@@ -2,4 +2,4 @@ package kubeslice
 
 // Ready implements the ready.Readiness interface, once this flips to true CoreDNS
 // assumes this plugin is ready for queries; it is not checked again.
-func (ks Kubeslice) Ready() bool { return true }
+func (ks *Kubeslice) Ready() bool { return true }

plugin/kubeslice/setup.go

@@ -1,10 +1,11 @@
 package kubeslice
 
 import (
+	"os"
+
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/core/dnsserver"
 	"github.com/coredns/coredns/plugin"
-	"os"
 
 	dnsCache "github.com/kubeslice/dns/plugin/kubeslice/cache"
 	kubeslicev1beta1 "github.com/kubeslice/worker-operator/api/v1beta1"
@@ -30,6 +31,7 @@ func init() { plugin.Register("kubeslice", setup) }
 // setup is the function that gets called when the config parser see the token "example". Setup is responsible
 // for parsing any extra options the example plugin may have. The first token this function sees is "example".
 func setup(c *caddy.Controller) error {
+	f := New()
 	c.Next() // Ignore "example" and give us the next token.
 	if c.NextArg() {
 		// If there was another token, return an error, because we don't have any configuration.
@@ -42,7 +44,9 @@ func setup(c *caddy.Controller) error {
 
 	// Add the Plugin to CoreDNS, so Servers can use it in their plugin chain.
 	dnsserver.GetConfig(c).AddPlugin(func(next plugin.Handler) plugin.Handler {
-		return Kubeslice{Next: next, EndpointsCache: cache}
+		f.Next = next
+		f.EndpointsCache = cache
+		return f
 	})
 
 	mgr, err := manager.New(