add wildcard warnings (#5030)

Signed-off-by: Chris O'Haver <cohaver@infoblox.com>

plugin/kubernetes/setup.go

@@ -7,6 +7,8 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"sync/atomic"
+	"time"
 
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/core/dnsserver"
@@ -61,6 +63,25 @@ func setup(c *caddy.Controller) error {
 		return nil
 	})
 
+	wildWarner := time.NewTicker(10 * time.Second)
+	c.OnStartup(func() error {
+		go func() {
+			for {
+				select {
+				case <-wildWarner.C:
+					if wc := atomic.SwapUint64(&wildCount, 0); wc > 0 {
+						log.Warningf("%d deprecated wildcard queries received. Wildcard queries will no longer be supported in the next minor release.", wc)
+					}
+				}
+			}
+		}()
+		return nil
+	})
+	c.OnShutdown(func() error {
+		wildWarner.Stop()
+		return nil
+	})
+
 	return nil
 }