plugin/kubernetes : make kubernetes client log in CoreDNS format (#5461)

Signed-off-by: Ondřej Benkovský <ondrej.benkovsky@jamf.com>

plugin/kubernetes/logger.go

+package kubernetes
+
+import (
+	clog "github.com/coredns/coredns/plugin/pkg/log"
+
+	"github.com/go-logr/logr"
+)
+
+// loggerAdapter is a simple wrapper around CoreDNS plugin logger made to implement logr.LogSink interface, which is used
+// as part of klog library for logging in Kubernetes client. By using this adapter CoreDNS is able to log messages/errors from
+// kubernetes client in a CoreDNS logging format
+type loggerAdapter struct {
+	clog.P
+}
+
+func (l *loggerAdapter) Init(_ logr.RuntimeInfo) {
+}
+
+func (l *loggerAdapter) Enabled(_ int) bool {
+	// verbosity is controlled inside klog library, we do not need to do anything here
+	return true
+}
+
+func (l *loggerAdapter) Info(_ int, msg string, _ ...interface{}) {
+	l.P.Info(msg)
+}
+
+func (l *loggerAdapter) Error(_ error, msg string, _ ...interface{}) {
+	l.P.Error(msg)
+}
+
+func (l *loggerAdapter) WithValues(_ ...interface{}) logr.LogSink {
+	return l
+}
+
+func (l *loggerAdapter) WithName(_ string) logr.LogSink {
+	return l
+}

plugin/kubernetes/setup.go

@@ -4,7 +4,6 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"os"
 	"strconv"
 	"strings"
 
@@ -15,6 +14,7 @@ import (
 	clog "github.com/coredns/coredns/plugin/pkg/log"
 	"github.com/coredns/coredns/plugin/pkg/upstream"
 
+	"github.com/go-logr/logr"
 	"github.com/miekg/dns"
 	meta "k8s.io/apimachinery/pkg/apis/meta/v1"
 	_ "k8s.io/client-go/plugin/pkg/client/auth/gcp"       // pull this in here, because we want it excluded if plugin.cfg doesn't have k8s
@@ -32,7 +32,7 @@ func init() { plugin.Register(pluginName, setup) }
 
 func setup(c *caddy.Controller) error {
 	// Do not call klog.InitFlags(nil) here.  It will cause reload to panic.
-	klog.SetOutput(os.Stdout)
+	klog.SetLogger(logr.New(&loggerAdapter{log}))
 
 	k, err := kubernetesParse(c)
 	if err != nil {