Source external DNS queries from container namespace

Signed-off-by: Santhosh Manohar <[email protected]>

resolver.go

@@ -233,15 +233,26 @@ func (r *resolver) ServeDNS(w dns.ResponseWriter, query *dns.Msg) {
 		for i := 0; i < num; i++ {
 			log.Debugf("Querying ext dns %s:%s for %s[%d]", w.LocalAddr().Network(), r.extDNS[i], name, query.Question[0].Qtype)
 
-			c := &dns.Client{Net: w.LocalAddr().Network()}
-			addr := fmt.Sprintf("%s:%d", r.extDNS[i], 53)
+			var extConn net.Conn
+			r.sb.execFunc(func() {
+				addr := fmt.Sprintf("%s:%d", r.extDNS[i], 53)
+				extConn, r.err = net.Dial(w.LocalAddr().Network(), addr)
+			})
+
+			if r.err != nil {
+				continue
+			}
+
+			co := &dns.Conn{Conn: extConn}
+			co.WriteMsg(query)
+			resp, err = co.ReadMsg()
+			co.Close()
 
-			resp, _, err = c.Exchange(query, addr)
 			if err == nil {
 				resp.Compress = true
 				break
 			}
-			log.Errorf("external resolution failed, %s", err)
+			log.Debugf("external resolution failed, %s", err)
 		}
 		if resp == nil {
 			return

sandbox.go

@@ -391,6 +391,10 @@ func (sb *sandbox) ResolveIP(ip string) string {
 	return svc
 }
 
+func (sb *sandbox) execFunc(f func()) {
+	sb.osSbox.InvokeFunc(f)
+}
+
 func (sb *sandbox) ResolveName(name string) net.IP {
 	var ip net.IP